Cyclosporiasis

Infectious Disease MONDO:0005725 Pathograph 5 Show in embeddings browser parasitic intestinal disorder coccidiosis

Cyclosporiasis is an intestinal infection caused by the coccidian protozoan parasite Cyclospora cayetanensis, acquired through ingestion of sporulated oocysts on contaminated fresh produce or in water, and characterized by prolonged, often relapsing watery diarrhea, profound fatigue, anorexia, and weight loss.

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4
Pathophys.
1
Histopath.
10
Phenotypes
1
Gaps
5
Pathograph
3
Medical Actions
2
Subtypes
2
Differentials
1
Deep Research
🏷

Classifications

Harrison's Part
INFECTIOUS DISEASES
◆

Subtypes

2
Immunocompetent self-limited cyclosporiasis
In immunocompetent hosts the illness is a prolonged but ultimately self-limited diarrheal disease, though the course is protracted and often relapsing when untreated.
Show evidence (1 reference)
PMID:1928575 SUPPORT Human Clinical
"An unidentified organism was found in the stools of 55 immunocompetent patients who presented to the CIWEC Clinic in Kathmandu, Nepal"
Documents the prolonged, self-limited diarrheal illness in immunocompetent hosts.
Cyclosporiasis in immunocompromised hosts
In HIV-infected and other immunocompromised patients, Cyclospora frequently causes chronic diarrhea and may require prolonged therapy and secondary prophylaxis.
Show evidence (1 reference)
PMID:10836915 SUPPORT Human Clinical
"In developing countries, Isospora belli and Cyclospora cayetanensis frequently cause chronic diarrhea in HIV-infected patients."
Supports a distinct chronic-diarrhea phenotype in immunocompromised (HIV) hosts.
?

Discussions and Knowledge Gaps

1
What is the infectious dose of Cyclospora cayetanensis in humans, and which host and oocyst-viability factors determine whether ingestion of sporulated oocysts establishes infection? A CDC human challenge pilot study failed to infect any of seven healthy volunteers despite inocula of up to ~49,000 oocysts, leaving the minimal infectious dose, the role of host susceptibility, and the required post-sporulation oocyst maturation/viability unresolved.
KNOWLEDGE GAP OPEN gap_cyclospora_infectious_dose
Attached to
pathophysiology#Ingestion of sporulated Cyclospora oocysts
Because oocysts must sporulate in the environment for days to weeks before becoming infective, oocyst age and viability at the time of ingestion may be critical determinants of infectivity. The negative human challenge result suggests either a high infectious dose, unrecognized host-susceptibility requirements, or loss of oocyst viability in the prepared inoculum. This gap limits mechanistic modeling of transmission and controlled experimental reproduction of disease.
Proposed experiments
Controlled human infection dose-response study with viability-verified oocysts
controlled human infection model Relation: this experiment is of type this experiment type This experiment is of type controlled human infection model.
exp_cyclospora_dose_response_challenge
A controlled human infection model using freshly sporulated, viability-verified C. cayetanensis oocysts across graded doses to define the minimal infectious dose and characterize host-susceptibility factors, contingent on establishing reliable in vitro sporulation and viability assays.
Show evidence (1 reference)
PMID:15200870 SUPPORT Human Clinical
"The volunteers did not experience symptoms of gastroenteritis, and no oocysts were detected in any stool samples during the 16 weeks volunteers were monitored."
Documents the failed human challenge that leaves the infectious dose and host-susceptibility determinants unresolved.
⚙

Pathophysiology

4
Ingestion of sporulated Cyclospora oocysts
Infection begins with ingestion of environmentally sporulated oocysts; freshly passed oocysts are not infective, so transmission requires an environmental maturation interval of days to weeks.
Downstream
Excystation and invasion of small-intestinal enterocytes Ingested sporulated oocysts release sporozoites that invade small-bowel epithelial cells.
Show evidence (1 reference)
PMID:11049789 SUPPORT Other
"One of the surprises has been the fact that a parasite that likely requires days to weeks outside the host to become infectious has repeatedly caused foodborne outbreaks, including large multistate outbreaks in the United States and Canada."
Supports the environmental sporulation requirement as the initiating epidemiologic step.
Excystation and invasion of small-intestinal enterocytes
Sporozoites excyst in the small intestine and invade enterocytes, where the parasite completes asexual and sexual developmental stages within parasitophorous vacuoles at the luminal end of the epithelial cells.
enterocyte CL:0000584 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves enterocyte (CL:0000584). CL:0000584 is a cell type from the Cell Ontology.
entry into host enterocyte GO:0044409 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves entry into host enterocyte, annotated with symbiont entry into host (GO:0044409). GO:0044409 is a biological process from the Gene Ontology.
jejunum UBERON:0002115 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in jejunum (UBERON:0002115). UBERON:0002115 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Villous atrophy and mucosal inflammation Intraepithelial parasitism drives small-bowel architectural injury.
Show evidence (1 reference)
PMID:9395371 SUPPORT Human Clinical
"Type I and II meronts, with 8-12 and 4 fully differentiated merozoites, respectively, were found at the luminal end of epithelial cells."
Documents intracellular meront (asexual) developmental stages within enterocytes.
Villous atrophy and mucosal inflammation
Small-bowel biopsies show villous shortening and widening with diffuse edema and a mixed inflammatory cell infiltrate, reflecting mucosal injury from intracellular infection.
inflammatory response GO:0006954 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves inflammatory response (GO:0006954). GO:0006954 is a biological process from the Gene Ontology.
Downstream
Malabsorption and diarrhea Loss of absorptive villous surface and mucosal injury impair absorption and drive watery diarrhea.
Show evidence (1 reference)
PMID:9395371 SUPPORT Human Clinical
"Jejunal biopsies showed an altered mucosal architecture with shortening and widening of the intestinal villi due to diffuse edema and infiltration by a mixed inflammatory cell infiltrate."
Supports villous atrophy and inflammatory infiltrate as the core mucosal lesion.
Malabsorption and diarrhea
Reduced absorptive surface area and epithelial dysfunction produce malabsorption and prolonged, often relapsing watery diarrhea, with associated anorexia, fatigue, and weight loss.
Downstream
Diarrhea Net fluid and nutrient malabsorption manifests as prolonged watery diarrhea.
Show evidence (1 reference)
PMID:1928575 SUPPORT Human Clinical
"The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
Supports the malabsorptive/diarrheal syndrome with constitutional features.
✶

Histopathology

1
Jejunal villous atrophy with inflammatory infiltrate
Jejunal biopsies show shortening and widening of intestinal villi with diffuse edema, mixed inflammatory infiltrate, and intracellular parasite stages within enterocytes.
Show evidence (1 reference)
PMID:9395371 SUPPORT Human Clinical
"Jejunal biopsies showed an altered mucosal architecture with shortening and widening of the intestinal villi due to diffuse edema and infiltration by a mixed inflammatory cell infiltrate."
Supports the characteristic jejunal histopathology of cyclosporiasis.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Cyclosporiasis Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

10
Digestive 4
Diarrhea VERY_FREQUENT HP:0002014 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Prolonged watery diarrhea, annotated with Diarrhea (HP:0002014), qualified as temporality prolonged. HP:0002014 is a phenotype from the Human Phenotype Ontology.
Temporal: PROLONGED
Show evidence (3 references)
PMID:1928575 SUPPORT Human Clinical
"The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
Supports prolonged watery diarrhea as the hallmark phenotype.
PMID:9772334 SUPPORT Other
"The parasite is associated with prolonged self-limiting and relapsing watery diarrhea, anorexia, fatigue, and sometimes myalgia."
Independent support for prolonged, relapsing watery diarrhea.
PMID:9605784 SUPPORT Human Clinical
"Commonly reported symptoms included diarrhea (100%), weight loss (93%), fatigue (91%), and anorexia (90%)."
Quantifies diarrhea as a near-universal symptom in an outbreak cohort.
Anorexia VERY_FREQUENT HP:0002039 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Anorexia (HP:0002039). HP:0002039 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:1928575 SUPPORT Human Clinical
"The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
Supports anorexia as a characteristic constitutional symptom.
PMID:9605784 SUPPORT Human Clinical
"Commonly reported symptoms included diarrhea (100%), weight loss (93%), fatigue (91%), and anorexia (90%)."
Quantifies anorexia at 90% of cases, supporting a very frequent band.
Nausea FREQUENT HP:0002018 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nausea (HP:0002018). HP:0002018 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:9395371 SUPPORT Human Clinical
"Patients presented with gastrointestinal symptoms, including diarrhea, flatulence, weight loss, abdominal discomfort, and nausea."
Supports nausea as a common gastrointestinal symptom.
Flatulence FREQUENT HP:0033589 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Flatulence (HP:0033589). HP:0033589 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:9395371 SUPPORT Human Clinical
"Patients presented with gastrointestinal symptoms, including diarrhea, flatulence, weight loss, abdominal discomfort, and nausea."
Supports flatulence as a common gastrointestinal symptom.
Metabolism 1
Fever OCCASIONAL HP:0001945 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Low-grade fever, annotated with Fever (HP:0001945). HP:0001945 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:9772334 SUPPORT Other
"Fever is infrequent."
Supports fever as an infrequent (occasional) manifestation.
Constitutional 3
Fatigue VERY_FREQUENT HP:0012378 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Fatigue (HP:0012378). HP:0012378 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:1928575 SUPPORT Human Clinical
"The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
Supports fatigue as a characteristic constitutional symptom.
PMID:9605784 SUPPORT Human Clinical
"Commonly reported symptoms included diarrhea (100%), weight loss (93%), fatigue (91%), and anorexia (90%)."
Quantifies fatigue at 91% of cases, supporting a very frequent band.
Abdominal pain FREQUENT HP:0002027 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abdominal discomfort, annotated with Abdominal pain (HP:0002027). HP:0002027 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:9395371 SUPPORT Human Clinical
"Patients presented with gastrointestinal symptoms, including diarrhea, flatulence, weight loss, abdominal discomfort, and nausea."
Supports abdominal discomfort/pain as a common symptom.
Myalgia OCCASIONAL HP:0003326 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Myalgia (HP:0003326). HP:0003326 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:9772334 SUPPORT Other
"The parasite is associated with prolonged self-limiting and relapsing watery diarrhea, anorexia, fatigue, and sometimes myalgia."
Supports myalgia as an occasional associated symptom.
Growth 1
Weight loss VERY_FREQUENT HP:0001824 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Weight loss (HP:0001824). HP:0001824 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:1928575 SUPPORT Human Clinical
"The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
Supports weight loss as a characteristic feature of protracted infection.
PMID:9605784 SUPPORT Human Clinical
"Commonly reported symptoms included diarrhea (100%), weight loss (93%), fatigue (91%), and anorexia (90%)."
Quantifies weight loss at 93% of cases, supporting a very frequent band.
PMID:9395371 SUPPORT Human Clinical
"Patients presented with gastrointestinal symptoms, including diarrhea, flatulence, weight loss, abdominal discomfort, and nausea."
Independent clinical support for weight loss in cyclosporiasis.
Other 1
Acalculous cholecystitis VERY_RARE HP:0001082 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Acalculous cholecystitis, annotated with Cholecystitis (HP:0001082). HP:0001082 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:11702292 SUPPORT Human Clinical
"We report a case of acalculous cholecystitis in a person with acquired immunodeficiency syndrome who required cholecystectomy and demonstrated C. cayetanensis in the gallbladder epithelium."
Documents histologically proven biliary (acalculous cholecystitis) involvement in an immunocompromised host.
💊

Medical Actions

3
Trimethoprim-sulfamethoxazole (co-trimoxazole)
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: trimethoprim CHEBI:45924 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses trimethoprim (CHEBI:45924). CHEBI:45924 is a therapeutic agent from Chemical Entities of Biological Interest. sulfamethoxazole CHEBI:9332 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses sulfamethoxazole (CHEBI:9332). CHEBI:9332 is a therapeutic agent from Chemical Entities of Biological Interest.
Trimethoprim-sulfamethoxazole is the first-line therapy for cyclosporiasis, producing rapid parasitologic and clinical cure in a placebo-controlled trial and effective in immunocompromised hosts with secondary prophylaxis.
Show evidence (3 references)
PMID:7885125 SUPPORT Human Clinical
"Treatment with co-trimoxazole for 7 days was effective in curing cyclospora infection among an expatriate population in Nepal."
Randomized placebo-controlled evidence that co-trimoxazole cures cyclosporiasis.
PMID:7885125 SUPPORT Human Clinical
"After 7 days, cyclospora was detected in 1 (6%) of 16 patients treated with co-trimoxazole who submitted stool specimens compared with 15 (88%) of 17 patients receiving placebo"
Quantifies parasitologic clearance versus placebo.
PMID:10836915 SUPPORT Human Clinical
"A 1-week course of trimethoprim-sulfamethoxazole is effective in HIV-infected patients with cyclosporiasis or isosporiasis."
Supports efficacy in immunocompromised (HIV) hosts.
Ciprofloxacin (alternative for sulfa-intolerant patients)
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: ciprofloxacin CHEBI:100241 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses ciprofloxacin (CHEBI:100241). CHEBI:100241 is a therapeutic agent from Chemical Entities of Biological Interest.
Ciprofloxacin is a second-line alternative for patients who cannot take sulfonamides, though it is somewhat less effective than trimethoprim-sulfamethoxazole.
Show evidence (1 reference)
PMID:10836915 SUPPORT Human Clinical
"it is acceptable for patients who cannot tolerate trimethoprim-sulfamethoxazole."
Supports ciprofloxacin as an acceptable alternative for patients who cannot tolerate TMP-SMX.
Oral rehydration and supportive care
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Fluid and electrolyte replacement is standard supportive care for the prolonged diarrheal illness alongside antiparasitic therapy.
Show evidence (1 reference)
PMID:7885125 SUPPORT Human Clinical
"The average duration of symptoms is more than three weeks, and no specific treatment has been shown to shorten the illness."
The protracted diarrheal course underlies the need for supportive rehydration during illness.
🌍

Environmental Factors

1
Consumption of contaminated fresh produce or water
Ingestion of fresh produce or water contaminated with sporulated oocysts is the principal environmental exposure driving infection and outbreaks.
Show evidence (1 reference)
PMID:11049789 SUPPORT Other
"One of the surprises has been the fact that a parasite that likely requires days to weeks outside the host to become infectious has repeatedly caused foodborne outbreaks, including large multistate outbreaks in the United States and Canada."
Supports contaminated food/water as the environmental driver of outbreaks.
🔬

Diagnosis

2
Modified acid-fast staining of stool oocysts
Cyclospora oocysts (8-9 microns in diameter) are detected in stool by modified acid-fast staining, in which they stain variably red; they are larger than Cryptosporidium oocysts, aiding differentiation.
microscopy NCIT:C16853 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:1928575 SUPPORT Human Clinical
"The organism is 8.0-9.0 microns in diameter, floats in Sheather's solution, and stains red with the modified acid-fast stain."
Supports modified acid-fast microscopy and oocyst size as the classic diagnostic approach.
Multiplex PCR stool gastrointestinal panel
Syndromic multiplex-PCR gastrointestinal panels now detect C. cayetanensis DNA in stool alongside other enteric protozoa, offering high sensitivity and rapid detection compared with microscopy.
polymerase chain reaction NCIT:C17003 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:32326453 SUPPORT Human Clinical
"The recently marketed assay AllplexTM Gastrointestinal Panel-Parasite Assay (GIPPA) (Seegene, Seoul, Korea) is able to detect most protozoa pathogens, i.e., Giardia duodenalis, Cryptosporidium spp., Entamoeba histolytica, Dientamoeba fragilis, Blastocystis hominis, and Cyclospora cayetanensis."
Documents a multiplex PCR stool panel that specifically detects C. cayetanensis.
PMID:32326453 SUPPORT Human Clinical
"The sensitivity reached 100% for C. cayetanensis (4/4), Cryptosporidium spp. (26/26), and B. hominis (26/26) positive samples."
Supports high multiplex-PCR sensitivity for C. cayetanensis versus microscopy.
📈

Progression

4
Incubation
Incubation: 7 days
The median incubation period is approximately one week, as characterized in point-source foodborne outbreaks.
Show evidence (1 reference)
PMID:9605784 SUPPORT Human Clinical
"The epidemic curve was consistent with a point source outbreak with a median incubation period of 7 days."
Supports a median incubation period of about one week.
Prolonged untreated illness
Untreated illness is protracted, with average symptom duration exceeding three weeks and no self-treatment shown to shorten it.
Show evidence (1 reference)
PMID:7885125 SUPPORT Human Clinical
"The average duration of symptoms is more than three weeks, and no specific treatment has been shown to shorten the illness."
Supports the characteristically protracted untreated course.
Relapsing course
The diarrheal illness is characteristically relapsing/remitting before resolution or treatment.
Show evidence (1 reference)
PMID:9772334 SUPPORT Other
"The parasite is associated with prolonged self-limiting and relapsing watery diarrhea, anorexia, fatigue, and sometimes myalgia."
Supports the relapsing nature of the diarrheal course.
Chronic infection in immunocompromised hosts
In HIV-infected patients, Cyclospora frequently produces chronic diarrhea that may require prolonged therapy and secondary prophylaxis.
Show evidence (1 reference)
PMID:10836915 SUPPORT Human Clinical
"In developing countries, Isospora belli and Cyclospora cayetanensis frequently cause chronic diarrhea in HIV-infected patients."
Supports chronic progression in immunocompromised hosts.
🌍

Epidemiology

2
Traveler's diarrhea and endemic exposure
Cyclospora is an established cause of traveler's diarrhea and is distributed worldwide, causing infection in healthy adults and children as well as in returning travelers.
international travel to endemic regions consumption of contaminated produce or water
Show evidence (2 references)
PMID:20065331 SUPPORT Other
"Since then, Cyclospora has been considered a cause of traveler's diarrhea."
Supports Cyclospora as a recognized cause of traveler's diarrhea.
PMID:9772334 SUPPORT Other
"In recent years, several studies have shown that Cyclospora is not a rare opportunistic pathogen but rather is the cause of common, worldwide intestinal infections in healthy adults and children."
Supports worldwide distribution and infection of immunocompetent adults and children.
Proportion of traveler's diarrhea attributable to Cyclospora
In a traveler cohort, Cyclospora accounted for a small but distinct fraction of traveler's diarrhea cases.
returning travelers with diarrhea
Show evidence (1 reference)
PMID:8588145 SUPPORT Human Clinical
"CLB was found in 2.8% of all cases of traveller's diarrhea in our series."
Quantifies the fraction of traveler's diarrhea attributable to Cyclospora in this cohort.
🦠

Infectious Agent

1
Cyclospora cayetanensis
Obligate intracellular apicomplexan coccidian parasite; the species of the genus Cyclospora established as a human enteric pathogen. Oocysts are shed unsporulated in feces and require days to weeks in the environment to sporulate and become infective, which precludes direct person-to-person transmission.
Cyclospora cayetanensis NCBITaxon:88456 NCBI Taxonomy (NCBITaxon)
Show evidence (2 references)
PMID:20065331 SUPPORT Other
"The coccidian parasite Cyclospora cayetanensis is recognized as an emerging pathogen that causes protracted diarrhea in humans."
Identifies C. cayetanensis as the coccidian etiologic agent of protracted diarrheal disease.
PMID:11049789 SUPPORT Other
"One of the surprises has been the fact that a parasite that likely requires days to weeks outside the host to become infectious has repeatedly caused foodborne outbreaks, including large multistate outbreaks in the United States and Canada."
Supports the environmental sporulation requirement that precludes direct person-to-person spread.
↔️

Transmission

2
Foodborne transmission via contaminated fresh produce
Ingestion of sporulated oocysts on contaminated fresh produce is the dominant recognized route in documented outbreaks, notably large multistate outbreaks in the United States and Canada.
Show evidence (2 references)
PMID:11049789 SUPPORT Other
"One of the surprises has been the fact that a parasite that likely requires days to weeks outside the host to become infectious has repeatedly caused foodborne outbreaks, including large multistate outbreaks in the United States and Canada."
Supports foodborne outbreak transmission as a principal recognized route.
PMID:9605784 SUPPORT Human Clinical
"containing raspberries, strawberries, blackberries, and blueberries."
Implicates fresh berries as the specific produce vehicle in a foodborne outbreak.
Waterborne and fecal-oral transmission
Ingestion of water or food contaminated with sporulated oocysts via the oro-fecal route, particularly in endemic tropical and subtropical regions.
Show evidence (1 reference)
PMID:11049789 SUPPORT Other
"the foodborne and waterborne outbreaks of cyclosporiasis that were documented from 1990 through 1999"
Supports both foodborne and waterborne routes documented in outbreak surveillance.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Cyclosporiasis:

Cryptosporidiosis Not Yet Curated MONDO:0015474
Overlapping Features Another coccidian diarrheal infection with overlapping watery diarrhea and similar acid-fast staining; Cyclospora oocysts are larger and could be misdiagnosed as Cryptosporidium.
Distinguishing Features
  • Cyclospora oocysts are 8-9 microns, roughly twice the diameter of Cryptosporidium oocysts.
  • Both stain with modified acid-fast; Cyclospora oocysts autofluoresce under UV microscopy.
Show evidence (1 reference)
PMID:1928575 SUPPORT Human Clinical
"Since the agent was closely associated with a prolonged, self-limited diarrheal illness, it could easily have been misdiagnosed as Cryptosporidium."
Supports cryptosporidiosis as a key differential owing to overlapping presentation.
Isosporiasis Not Yet Curated MONDO:0018769
Overlapping Features Cystoisospora (Isospora) belli is a related coccidian that also causes chronic diarrhea in immunocompromised hosts and responds to the same trimethoprim-sulfamethoxazole therapy.
Distinguishing Features
  • Cystoisospora oocysts are larger and elliptical, distinguishable on stool microscopy.
  • Both frequently cause chronic diarrhea in HIV-infected patients and both respond to TMP-SMX.
Show evidence (1 reference)
PMID:10836915 SUPPORT Human Clinical
"In developing countries, Isospora belli and Cyclospora cayetanensis frequently cause chronic diarrhea in HIV-infected patients."
Supports isosporiasis as a clinically overlapping coccidian differential.
{ }

Source YAML

click to show 
name: Cyclosporiasis
creation_date: '2026-07-09T00:00:00Z'
category: Infectious Disease
description: >-
  Cyclosporiasis is an intestinal infection caused by the coccidian protozoan
  parasite Cyclospora cayetanensis, acquired through ingestion of sporulated
  oocysts on contaminated fresh produce or in water, and characterized by
  prolonged, often relapsing watery diarrhea, profound fatigue, anorexia, and
  weight loss.
disease_term:
  preferred_term: cyclosporiasis
  term:
    id: MONDO:0005725
    label: cyclosporiasis
parents:
- parasitic intestinal disorder
- coccidiosis
synonyms:
- Cyclospora infection
- Cyclospora cayetanensis infection
- cyclosporosis
classifications:
  harrisons_chapter:
  - classification_value: INFECTIOUS_DISEASES
    evidence:
    - reference: PMID:20065331
      reference_title: "Update on Cyclospora cayetanensis, a food-borne and waterborne parasite."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "The coccidian parasite Cyclospora cayetanensis is recognized as an emerging pathogen that causes protracted diarrhea in humans."
      explanation: Supports classification as a protozoan (coccidian) enteric infectious disease.
has_subtypes:
- name: Immunocompetent
  display_name: Immunocompetent self-limited cyclosporiasis
  classification: clinical_course
  description: >-
    In immunocompetent hosts the illness is a prolonged but ultimately
    self-limited diarrheal disease, though the course is protracted and often
    relapsing when untreated.
  evidence:
  - reference: PMID:1928575
    reference_title: "An alga-like organism associated with an outbreak of prolonged diarrhea among foreigners in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "An unidentified organism was found in the stools of 55 immunocompetent patients who presented to the CIWEC Clinic in Kathmandu, Nepal"
    explanation: Documents the prolonged, self-limited diarrheal illness in immunocompetent hosts.
- name: Immunocompromised
  display_name: Cyclosporiasis in immunocompromised hosts
  classification: clinical_course
  description: >-
    In HIV-infected and other immunocompromised patients, Cyclospora
    frequently causes chronic diarrhea and may require prolonged therapy and
    secondary prophylaxis.
  evidence:
  - reference: PMID:10836915
    reference_title: "Trimethoprim-sulfamethoxazole compared with ciprofloxacin for treatment and prophylaxis of Isospora belli and Cyclospora cayetanensis infection in HIV-infected patients. A randomized, controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In developing countries, Isospora belli and Cyclospora cayetanensis frequently cause chronic diarrhea in HIV-infected patients."
    explanation: Supports a distinct chronic-diarrhea phenotype in immunocompromised (HIV) hosts.
infectious_agent:
- name: Cyclospora cayetanensis
  infectious_agent_term:
    preferred_term: Cyclospora cayetanensis
    term:
      id: NCBITaxon:88456
      label: Cyclospora cayetanensis
  description: >-
    Obligate intracellular apicomplexan coccidian parasite; the species of the
    genus Cyclospora established as a human enteric pathogen. Oocysts are shed
    unsporulated in feces and require days to weeks in the environment to
    sporulate and become infective, which precludes direct person-to-person
    transmission.
  evidence:
  - reference: PMID:20065331
    reference_title: "Update on Cyclospora cayetanensis, a food-borne and waterborne parasite."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The coccidian parasite Cyclospora cayetanensis is recognized as an emerging pathogen that causes protracted diarrhea in humans."
    explanation: Identifies C. cayetanensis as the coccidian etiologic agent of protracted diarrheal disease.
  - reference: PMID:11049789
    reference_title: "Cyclospora cayetanensis: a review, focusing on the outbreaks of cyclosporiasis in the 1990s."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "One of the surprises has been the fact that a parasite that likely requires days to weeks outside the host to become infectious has repeatedly caused foodborne outbreaks, including large multistate outbreaks in the United States and Canada."
    explanation: Supports the environmental sporulation requirement that precludes direct person-to-person spread.
transmission:
- name: Foodborne transmission via contaminated fresh produce
  description: >-
    Ingestion of sporulated oocysts on contaminated fresh produce is the
    dominant recognized route in documented outbreaks, notably large multistate
    outbreaks in the United States and Canada.
  evidence:
  - reference: PMID:11049789
    reference_title: "Cyclospora cayetanensis: a review, focusing on the outbreaks of cyclosporiasis in the 1990s."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "One of the surprises has been the fact that a parasite that likely requires days to weeks outside the host to become infectious has repeatedly caused foodborne outbreaks, including large multistate outbreaks in the United States and Canada."
    explanation: Supports foodborne outbreak transmission as a principal recognized route.
  - reference: PMID:9605784
    reference_title: "A foodborne outbreak of Cyclospora cayetanensis at a wedding: clinical features and risk factors for illness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "containing raspberries, strawberries, blackberries, and blueberries."
    explanation: Implicates fresh berries as the specific produce vehicle in a foodborne outbreak.
- name: Waterborne and fecal-oral transmission
  description: >-
    Ingestion of water or food contaminated with sporulated oocysts via the
    oro-fecal route, particularly in endemic tropical and subtropical regions.
  evidence:
  - reference: PMID:11049789
    reference_title: "Cyclospora cayetanensis: a review, focusing on the outbreaks of cyclosporiasis in the 1990s."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "the foodborne and waterborne outbreaks of cyclosporiasis that were documented from 1990 through 1999"
    explanation: Supports both foodborne and waterborne routes documented in outbreak surveillance.
epidemiology:
- name: Traveler's diarrhea and endemic exposure
  description: >-
    Cyclospora is an established cause of traveler's diarrhea and is
    distributed worldwide, causing infection in healthy adults and children as
    well as in returning travelers.
  factors:
  - international travel to endemic regions
  - consumption of contaminated produce or water
  evidence:
  - reference: PMID:20065331
    reference_title: "Update on Cyclospora cayetanensis, a food-borne and waterborne parasite."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Since then, Cyclospora has been considered a cause of traveler's diarrhea."
    explanation: Supports Cyclospora as a recognized cause of traveler's diarrhea.
  - reference: PMID:9772334
    reference_title: "Cyclosporiasis in a traveler returning from South America."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "In recent years, several studies have shown that Cyclospora is not a rare opportunistic pathogen but rather is the cause of common, worldwide intestinal infections in healthy adults and children."
    explanation: Supports worldwide distribution and infection of immunocompetent adults and children.
- name: Proportion of traveler's diarrhea attributable to Cyclospora
  description: >-
    In a traveler cohort, Cyclospora accounted for a small but distinct
    fraction of traveler's diarrhea cases.
  factors:
  - returning travelers with diarrhea
  unit: percent of traveler's diarrhea cases
  evidence:
  - reference: PMID:8588145
    reference_title: "Cyclospora in patients with traveller's diarrhea."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CLB was found in 2.8% of all cases of traveller's diarrhea in our series."
    explanation: Quantifies the fraction of traveler's diarrhea attributable to Cyclospora in this cohort.
progression:
- phase: Incubation
  incubation_days: '7'
  notes: >-
    The median incubation period is approximately one week, as characterized in
    point-source foodborne outbreaks.
  evidence:
  - reference: PMID:9605784
    reference_title: "A foodborne outbreak of Cyclospora cayetanensis at a wedding: clinical features and risk factors for illness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The epidemic curve was consistent with a point source outbreak with a median incubation period of 7 days."
    explanation: Supports a median incubation period of about one week.
- phase: Prolonged untreated illness
  notes: >-
    Untreated illness is protracted, with average symptom duration exceeding
    three weeks and no self-treatment shown to shorten it.
  evidence:
  - reference: PMID:7885125
    reference_title: "Placebo-controlled trial of co-trimoxazole for Cyclospora infections among travellers and foreign residents in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The average duration of symptoms is more than three weeks, and no specific treatment has been shown to shorten the illness."
    explanation: Supports the characteristically protracted untreated course.
- phase: Relapsing course
  notes: >-
    The diarrheal illness is characteristically relapsing/remitting before
    resolution or treatment.
  evidence:
  - reference: PMID:9772334
    reference_title: "Cyclosporiasis in a traveler returning from South America."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The parasite is associated with prolonged self-limiting and relapsing watery diarrhea, anorexia, fatigue, and sometimes myalgia."
    explanation: Supports the relapsing nature of the diarrheal course.
- phase: Chronic infection in immunocompromised hosts
  notes: >-
    In HIV-infected patients, Cyclospora frequently produces chronic diarrhea
    that may require prolonged therapy and secondary prophylaxis.
  evidence:
  - reference: PMID:10836915
    reference_title: "Trimethoprim-sulfamethoxazole compared with ciprofloxacin for treatment and prophylaxis of Isospora belli and Cyclospora cayetanensis infection in HIV-infected patients. A randomized, controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In developing countries, Isospora belli and Cyclospora cayetanensis frequently cause chronic diarrhea in HIV-infected patients."
    explanation: Supports chronic progression in immunocompromised hosts.
pathophysiology:
- name: Ingestion of sporulated Cyclospora oocysts
  description: >-
    Infection begins with ingestion of environmentally sporulated oocysts;
    freshly passed oocysts are not infective, so transmission requires an
    environmental maturation interval of days to weeks.
  downstream:
  - target: Excystation and invasion of small-intestinal enterocytes
    description: Ingested sporulated oocysts release sporozoites that invade small-bowel epithelial cells.
    evidence:
    - reference: PMID:9395371
      reference_title: "Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The intracellular life-cycle stages of these parasites in the enterocytes of patients will also be described."
      explanation: Supports establishment of intracellular infection within enterocytes after ingestion.
  evidence:
  - reference: PMID:11049789
    reference_title: "Cyclospora cayetanensis: a review, focusing on the outbreaks of cyclosporiasis in the 1990s."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "One of the surprises has been the fact that a parasite that likely requires days to weeks outside the host to become infectious has repeatedly caused foodborne outbreaks, including large multistate outbreaks in the United States and Canada."
    explanation: Supports the environmental sporulation requirement as the initiating epidemiologic step.
- name: Excystation and invasion of small-intestinal enterocytes
  description: >-
    Sporozoites excyst in the small intestine and invade enterocytes, where the
    parasite completes asexual and sexual developmental stages within
    parasitophorous vacuoles at the luminal end of the epithelial cells.
  cell_types:
  - preferred_term: enterocyte
    term:
      id: CL:0000584
      label: enterocyte
  locations:
  - preferred_term: jejunum
    term:
      id: UBERON:0002115
      label: jejunum
  biological_processes:
  - preferred_term: entry into host enterocyte
    term:
      id: GO:0044409
      label: symbiont entry into host
  downstream:
  - target: Villous atrophy and mucosal inflammation
    description: Intraepithelial parasitism drives small-bowel architectural injury.
    evidence:
    - reference: PMID:9395371
      reference_title: "Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Jejunal biopsies showed an altered mucosal architecture with shortening and widening of the intestinal villi due to diffuse edema and infiltration by a mixed inflammatory cell infiltrate."
      explanation: Links intraepithelial infection to villous shortening and inflammatory injury.
  evidence:
  - reference: PMID:9395371
    reference_title: "Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Type I and II meronts, with 8-12 and 4 fully differentiated merozoites, respectively, were found at the luminal end of epithelial cells."
    explanation: Documents intracellular meront (asexual) developmental stages within enterocytes.
- name: Villous atrophy and mucosal inflammation
  description: >-
    Small-bowel biopsies show villous shortening and widening with diffuse
    edema and a mixed inflammatory cell infiltrate, reflecting mucosal injury
    from intracellular infection.
  biological_processes:
  - preferred_term: inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
  downstream:
  - target: Malabsorption and diarrhea
    description: Loss of absorptive villous surface and mucosal injury impair absorption and drive watery diarrhea.
    evidence:
    - reference: PMID:9395371
      reference_title: "Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Patients presented with gastrointestinal symptoms, including diarrhea, flatulence, weight loss, abdominal discomfort, and nausea."
      explanation: Links the mucosal injury to the malabsorptive/diarrheal clinical presentation.
  evidence:
  - reference: PMID:9395371
    reference_title: "Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Jejunal biopsies showed an altered mucosal architecture with shortening and widening of the intestinal villi due to diffuse edema and infiltration by a mixed inflammatory cell infiltrate."
    explanation: Supports villous atrophy and inflammatory infiltrate as the core mucosal lesion.
- name: Malabsorption and diarrhea
  description: >-
    Reduced absorptive surface area and epithelial dysfunction produce
    malabsorption and prolonged, often relapsing watery diarrhea, with
    associated anorexia, fatigue, and weight loss.
  downstream:
  - target: Diarrhea
    description: Net fluid and nutrient malabsorption manifests as prolonged watery diarrhea.
    evidence:
    - reference: PMID:1928575
      reference_title: "An alga-like organism associated with an outbreak of prolonged diarrhea among foreigners in Nepal."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
      explanation: Links the malabsorptive process to the hallmark prolonged watery diarrhea and constitutional symptoms.
  evidence:
  - reference: PMID:1928575
    reference_title: "An alga-like organism associated with an outbreak of prolonged diarrhea among foreigners in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
    explanation: Supports the malabsorptive/diarrheal syndrome with constitutional features.
phenotypes:
- name: Diarrhea
  category: Gastrointestinal
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Prolonged watery diarrhea
    term:
      id: HP:0002014
      label: Diarrhea
    temporality: PROLONGED
  evidence:
  - reference: PMID:1928575
    reference_title: "An alga-like organism associated with an outbreak of prolonged diarrhea among foreigners in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
    explanation: Supports prolonged watery diarrhea as the hallmark phenotype.
  - reference: PMID:9772334
    reference_title: "Cyclosporiasis in a traveler returning from South America."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The parasite is associated with prolonged self-limiting and relapsing watery diarrhea, anorexia, fatigue, and sometimes myalgia."
    explanation: Independent support for prolonged, relapsing watery diarrhea.
  - reference: PMID:9605784
    reference_title: "A foodborne outbreak of Cyclospora cayetanensis at a wedding: clinical features and risk factors for illness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Commonly reported symptoms included diarrhea (100%), weight loss (93%), fatigue (91%), and anorexia (90%)."
    explanation: Quantifies diarrhea as a near-universal symptom in an outbreak cohort.
- name: Anorexia
  category: Constitutional
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Anorexia
    term:
      id: HP:0002039
      label: Anorexia
  evidence:
  - reference: PMID:1928575
    reference_title: "An alga-like organism associated with an outbreak of prolonged diarrhea among foreigners in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
    explanation: Supports anorexia as a characteristic constitutional symptom.
  - reference: PMID:9605784
    reference_title: "A foodborne outbreak of Cyclospora cayetanensis at a wedding: clinical features and risk factors for illness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Commonly reported symptoms included diarrhea (100%), weight loss (93%), fatigue (91%), and anorexia (90%)."
    explanation: Quantifies anorexia at 90% of cases, supporting a very frequent band.
- name: Fatigue
  category: Constitutional
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Fatigue
    term:
      id: HP:0012378
      label: Fatigue
  evidence:
  - reference: PMID:1928575
    reference_title: "An alga-like organism associated with an outbreak of prolonged diarrhea among foreigners in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
    explanation: Supports fatigue as a characteristic constitutional symptom.
  - reference: PMID:9605784
    reference_title: "A foodborne outbreak of Cyclospora cayetanensis at a wedding: clinical features and risk factors for illness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Commonly reported symptoms included diarrhea (100%), weight loss (93%), fatigue (91%), and anorexia (90%)."
    explanation: Quantifies fatigue at 91% of cases, supporting a very frequent band.
- name: Weight loss
  category: Constitutional
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Weight loss
    term:
      id: HP:0001824
      label: Weight loss
  evidence:
  - reference: PMID:1928575
    reference_title: "An alga-like organism associated with an outbreak of prolonged diarrhea among foreigners in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The illness was characterized by prolonged watery diarrhea, anorexia, fatigue, and weight loss."
    explanation: Supports weight loss as a characteristic feature of protracted infection.
  - reference: PMID:9605784
    reference_title: "A foodborne outbreak of Cyclospora cayetanensis at a wedding: clinical features and risk factors for illness."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Commonly reported symptoms included diarrhea (100%), weight loss (93%), fatigue (91%), and anorexia (90%)."
    explanation: Quantifies weight loss at 93% of cases, supporting a very frequent band.
  - reference: PMID:9395371
    reference_title: "Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients presented with gastrointestinal symptoms, including diarrhea, flatulence, weight loss, abdominal discomfort, and nausea."
    explanation: Independent clinical support for weight loss in cyclosporiasis.
- name: Abdominal pain
  category: Gastrointestinal
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Abdominal discomfort
    term:
      id: HP:0002027
      label: Abdominal pain
  evidence:
  - reference: PMID:9395371
    reference_title: "Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients presented with gastrointestinal symptoms, including diarrhea, flatulence, weight loss, abdominal discomfort, and nausea."
    explanation: Supports abdominal discomfort/pain as a common symptom.
- name: Nausea
  category: Gastrointestinal
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Nausea
    term:
      id: HP:0002018
      label: Nausea
  evidence:
  - reference: PMID:9395371
    reference_title: "Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients presented with gastrointestinal symptoms, including diarrhea, flatulence, weight loss, abdominal discomfort, and nausea."
    explanation: Supports nausea as a common gastrointestinal symptom.
- name: Flatulence
  category: Gastrointestinal
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Flatulence
    term:
      id: HP:0033589
      label: Flatulence
  evidence:
  - reference: PMID:9395371
    reference_title: "Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients presented with gastrointestinal symptoms, including diarrhea, flatulence, weight loss, abdominal discomfort, and nausea."
    explanation: Supports flatulence as a common gastrointestinal symptom.
- name: Myalgia
  category: Constitutional
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Myalgia
    term:
      id: HP:0003326
      label: Myalgia
  evidence:
  - reference: PMID:9772334
    reference_title: "Cyclosporiasis in a traveler returning from South America."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The parasite is associated with prolonged self-limiting and relapsing watery diarrhea, anorexia, fatigue, and sometimes myalgia."
    explanation: Supports myalgia as an occasional associated symptom.
- name: Fever
  category: Constitutional
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Low-grade fever
    term:
      id: HP:0001945
      label: Fever
  evidence:
  - reference: PMID:9772334
    reference_title: "Cyclosporiasis in a traveler returning from South America."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Fever is infrequent."
    explanation: Supports fever as an infrequent (occasional) manifestation.
- name: Acalculous cholecystitis
  category: Hepatobiliary
  frequency: VERY_RARE
  description: >-
    Biliary tract infection presenting as acalculous cholecystitis is a rare
    complication reported in immunocompromised (AIDS) hosts, in whom Cyclospora
    can infect the gallbladder epithelium.
  phenotype_term:
    preferred_term: Acalculous cholecystitis
    term:
      id: HP:0001082
      label: Cholecystitis
  evidence:
  - reference: PMID:11702292
    reference_title: "Histologic proof of acalculous cholecystitis due to Cyclospora cayetanensis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report a case of acalculous cholecystitis in a person with acquired immunodeficiency syndrome who required cholecystectomy and demonstrated C. cayetanensis in the gallbladder epithelium."
    explanation: Documents histologically proven biliary (acalculous cholecystitis) involvement in an immunocompromised host.
diagnosis:
- name: Modified acid-fast staining of stool oocysts
  description: >-
    Cyclospora oocysts (8-9 microns in diameter) are detected in stool by
    modified acid-fast staining, in which they stain variably red; they are
    larger than Cryptosporidium oocysts, aiding differentiation.
  diagnosis_term:
    preferred_term: microscopy
    term:
      id: NCIT:C16853
      label: Microscopy
  evidence:
  - reference: PMID:1928575
    reference_title: "An alga-like organism associated with an outbreak of prolonged diarrhea among foreigners in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The organism is 8.0-9.0 microns in diameter, floats in Sheather's solution, and stains red with the modified acid-fast stain."
    explanation: Supports modified acid-fast microscopy and oocyst size as the classic diagnostic approach.
- name: Multiplex PCR stool gastrointestinal panel
  description: >-
    Syndromic multiplex-PCR gastrointestinal panels now detect C. cayetanensis
    DNA in stool alongside other enteric protozoa, offering high sensitivity and
    rapid detection compared with microscopy.
  diagnosis_term:
    preferred_term: polymerase chain reaction
    term:
      id: NCIT:C17003
      label: Polymerase Chain Reaction
  evidence:
  - reference: PMID:32326453
    reference_title: "Evaluation of the Allplex(TM) Gastrointestinal Panel-Parasite Assay for Protozoa Detection in Stool Samples: A Retrospective and Prospective Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The recently marketed assay AllplexTM Gastrointestinal Panel-Parasite Assay (GIPPA) (Seegene, Seoul, Korea) is able to detect most protozoa pathogens, i.e., Giardia duodenalis, Cryptosporidium spp., Entamoeba histolytica, Dientamoeba fragilis, Blastocystis hominis, and Cyclospora cayetanensis."
    explanation: Documents a multiplex PCR stool panel that specifically detects C. cayetanensis.
  - reference: PMID:32326453
    reference_title: "Evaluation of the Allplex(TM) Gastrointestinal Panel-Parasite Assay for Protozoa Detection in Stool Samples: A Retrospective and Prospective Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The sensitivity reached 100% for C. cayetanensis (4/4), Cryptosporidium spp. (26/26), and B. hominis (26/26) positive samples."
    explanation: Supports high multiplex-PCR sensitivity for C. cayetanensis versus microscopy.
differential_diagnoses:
- name: Cryptosporidiosis
  description: >-
    Another coccidian diarrheal infection with overlapping watery diarrhea and
    similar acid-fast staining; Cyclospora oocysts are larger and could be
    misdiagnosed as Cryptosporidium.
  disease_term:
    preferred_term: cryptosporidiosis
    term:
      id: MONDO:0015474
      label: cryptosporidiosis
  distinguishing_features:
  - Cyclospora oocysts are 8-9 microns, roughly twice the diameter of Cryptosporidium oocysts.
  - Both stain with modified acid-fast; Cyclospora oocysts autofluoresce under UV microscopy.
  evidence:
  - reference: PMID:1928575
    reference_title: "An alga-like organism associated with an outbreak of prolonged diarrhea among foreigners in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Since the agent was closely associated with a prolonged, self-limited diarrheal illness, it could easily have been misdiagnosed as Cryptosporidium."
    explanation: Supports cryptosporidiosis as a key differential owing to overlapping presentation.
- name: Isosporiasis
  description: >-
    Cystoisospora (Isospora) belli is a related coccidian that also causes
    chronic diarrhea in immunocompromised hosts and responds to the same
    trimethoprim-sulfamethoxazole therapy.
  disease_term:
    preferred_term: isosporiasis
    term:
      id: MONDO:0018769
      label: isosporiasis
  distinguishing_features:
  - Cystoisospora oocysts are larger and elliptical, distinguishable on stool microscopy.
  - Both frequently cause chronic diarrhea in HIV-infected patients and both respond to TMP-SMX.
  evidence:
  - reference: PMID:10836915
    reference_title: "Trimethoprim-sulfamethoxazole compared with ciprofloxacin for treatment and prophylaxis of Isospora belli and Cyclospora cayetanensis infection in HIV-infected patients. A randomized, controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In developing countries, Isospora belli and Cyclospora cayetanensis frequently cause chronic diarrhea in HIV-infected patients."
    explanation: Supports isosporiasis as a clinically overlapping coccidian differential.
treatments:
- name: Trimethoprim-sulfamethoxazole (co-trimoxazole)
  description: >-
    Trimethoprim-sulfamethoxazole is the first-line therapy for cyclosporiasis,
    producing rapid parasitologic and clinical cure in a placebo-controlled
    trial and effective in immunocompromised hosts with secondary prophylaxis.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: trimethoprim
      term:
        id: CHEBI:45924
        label: trimethoprim
    - preferred_term: sulfamethoxazole
      term:
        id: CHEBI:9332
        label: sulfamethoxazole
  evidence:
  - reference: PMID:7885125
    reference_title: "Placebo-controlled trial of co-trimoxazole for Cyclospora infections among travellers and foreign residents in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment with co-trimoxazole for 7 days was effective in curing cyclospora infection among an expatriate population in Nepal."
    explanation: Randomized placebo-controlled evidence that co-trimoxazole cures cyclosporiasis.
  - reference: PMID:7885125
    reference_title: "Placebo-controlled trial of co-trimoxazole for Cyclospora infections among travellers and foreign residents in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "After 7 days, cyclospora was detected in 1 (6%) of 16 patients treated with co-trimoxazole who submitted stool specimens compared with 15 (88%) of 17 patients receiving placebo"
    explanation: Quantifies parasitologic clearance versus placebo.
  - reference: PMID:10836915
    reference_title: "Trimethoprim-sulfamethoxazole compared with ciprofloxacin for treatment and prophylaxis of Isospora belli and Cyclospora cayetanensis infection in HIV-infected patients. A randomized, controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 1-week course of trimethoprim-sulfamethoxazole is effective in HIV-infected patients with cyclosporiasis or isosporiasis."
    explanation: Supports efficacy in immunocompromised (HIV) hosts.
- name: Ciprofloxacin (alternative for sulfa-intolerant patients)
  description: >-
    Ciprofloxacin is a second-line alternative for patients who cannot take
    sulfonamides, though it is somewhat less effective than
    trimethoprim-sulfamethoxazole.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ciprofloxacin
      term:
        id: CHEBI:100241
        label: ciprofloxacin
  evidence:
  - reference: PMID:10836915
    reference_title: "Trimethoprim-sulfamethoxazole compared with ciprofloxacin for treatment and prophylaxis of Isospora belli and Cyclospora cayetanensis infection in HIV-infected patients. A randomized, controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "it is acceptable for patients who cannot tolerate trimethoprim-sulfamethoxazole."
    explanation: Supports ciprofloxacin as an acceptable alternative for patients who cannot tolerate TMP-SMX.
- name: Oral rehydration and supportive care
  description: >-
    Fluid and electrolyte replacement is standard supportive care for the
    prolonged diarrheal illness alongside antiparasitic therapy.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:7885125
    reference_title: "Placebo-controlled trial of co-trimoxazole for Cyclospora infections among travellers and foreign residents in Nepal."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The average duration of symptoms is more than three weeks, and no specific treatment has been shown to shorten the illness."
    explanation: The protracted diarrheal course underlies the need for supportive rehydration during illness.
environmental:
- name: Consumption of contaminated fresh produce or water
  description: >-
    Ingestion of fresh produce or water contaminated with sporulated oocysts is
    the principal environmental exposure driving infection and outbreaks.
  effect: Increases risk of foodborne and waterborne cyclosporiasis.
  evidence:
  - reference: PMID:11049789
    reference_title: "Cyclospora cayetanensis: a review, focusing on the outbreaks of cyclosporiasis in the 1990s."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "One of the surprises has been the fact that a parasite that likely requires days to weeks outside the host to become infectious has repeatedly caused foodborne outbreaks, including large multistate outbreaks in the United States and Canada."
    explanation: Supports contaminated food/water as the environmental driver of outbreaks.
histopathology:
- name: Jejunal villous atrophy with inflammatory infiltrate
  description: >-
    Jejunal biopsies show shortening and widening of intestinal villi with
    diffuse edema, mixed inflammatory infiltrate, and intracellular parasite
    stages within enterocytes.
  evidence:
  - reference: PMID:9395371
    reference_title: "Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Jejunal biopsies showed an altered mucosal architecture with shortening and widening of the intestinal villi due to diffuse edema and infiltration by a mixed inflammatory cell infiltrate."
    explanation: Supports the characteristic jejunal histopathology of cyclosporiasis.
discussions:
- discussion_id: gap_cyclospora_infectious_dose
  prompt: >-
    What is the infectious dose of Cyclospora cayetanensis in humans, and which
    host and oocyst-viability factors determine whether ingestion of sporulated
    oocysts establishes infection? A CDC human challenge pilot study failed to
    infect any of seven healthy volunteers despite inocula of up to ~49,000
    oocysts, leaving the minimal infectious dose, the role of host
    susceptibility, and the required post-sporulation oocyst maturation/viability
    unresolved.
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Ingestion of sporulated Cyclospora oocysts
  rationale: >-
    Because oocysts must sporulate in the environment for days to weeks before
    becoming infective, oocyst age and viability at the time of ingestion may be
    critical determinants of infectivity. The negative human challenge result
    suggests either a high infectious dose, unrecognized host-susceptibility
    requirements, or loss of oocyst viability in the prepared inoculum. This gap
    limits mechanistic modeling of transmission and controlled experimental
    reproduction of disease.
  proposed_experiments:
  - experiment_id: exp_cyclospora_dose_response_challenge
    name: Controlled human infection dose-response study with viability-verified oocysts
    description: >-
      A controlled human infection model using freshly sporulated,
      viability-verified C. cayetanensis oocysts across graded doses to define
      the minimal infectious dose and characterize host-susceptibility factors,
      contingent on establishing reliable in vitro sporulation and viability
      assays.
    experiment_type:
      preferred_term: controlled human infection model
  evidence:
  - reference: PMID:15200870
    reference_title: "Human challenge pilot study with Cyclospora cayetanensis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The volunteers did not experience symptoms of gastroenteritis, and no oocysts were detected in any stool samples during the 16 weeks volunteers were monitored."
    explanation: Documents the failed human challenge that leaves the infectious dose and host-susceptibility determinants unresolved.
biochemical: []
genetic: []
datasets: []
📚

References & Deep Research

Deep Research

1
Claude Code ▸
Cyclosporiasis (*Cyclospora cayetanensis* infection): Comprehensive Research Report
claude-haiku-4-5-20251001, claude-sonnet-5 32 citations 2026-07-09T14:13:35.160669

Cyclosporiasis (Cyclospora cayetanensis infection): Comprehensive Research Report

1. Disease Information

Overview: Cyclosporiasis is a foodborne/waterborne diarrheal illness caused by Cyclospora cayetanensis, a coccidian (apicomplexan) protozoan parasite. Humans are the only known host — no animal reservoir has been identified — and transmission occurs via ingestion of sporulated oocysts contaminating fresh produce or water; there is no direct person-to-person transmission because freshly passed oocysts require days-to-weeks of environmental sporulation before becoming infectious (CDC DPDx; PMC6780905, Cyclospora cayetanensis and Cyclosporiasis: An Update).

Key identifiers: - ICD-10-CM: A07.4 (Cyclosporiasis) - MONDO: MONDO:0005725 - Disease Ontology: DOID:12750 - Orphanet: ORPHA210 - SNOMED CT: 240372001 - UMLS: C0343398 - NCBI Taxonomy (organism): Cyclospora cayetanensis, txid88456 - MeSH: Cyclosporiasis (D019022); Organism: Cyclospora (D019081)

Synonyms: Cyclospora infection, Cyclospora cayetanensis infection, "cyanobacterium-like body" (CLB) diarrhea (historical name before speciation in 1993-94), coccidian-associated diarrhea.

Evidence basis: Aggregated disease-level knowledge (case series, outbreak investigations, systematic reviews) predominates; some individual pathologic/histologic case reports exist (e.g., PMID:9395371).

2. Etiology

Causal agent: Infection is caused by ingestion of sporulated oocysts of C. cayetanensis (an obligate intracellular coccidian parasite of the family Eimeriidae). This is an infectious, not genetic, disease — there is no known Mendelian susceptibility locus, though host immune status strongly modulates severity.

A newly recognized taxonomic wrinkle (2023): CDC researchers demonstrated that clinical "C. cayetanensis" cyclosporiasis is actually caused by at least three genetically distinct species/lineages — the classic C. cayetanensis (with lineages A and B distinguished at the CDS3 and 360i2 nuclear loci) plus two novel species, Cyclospora ashfordi sp. nov. and Cyclospora henanensis sp. nov. (isolated from a Henan, China strain), all causing indistinguishable human cyclosporiasis (PMC10090632, Parasitology 2023, "Cyclospora cayetanensis comprises at least 3 species that cause human cyclosporiasis"; CDC AMD success story).

Risk factors: - Environmental/behavioral: Consumption of imported fresh produce (basil, cilantro, raspberries, snow peas, mesclun/salad mix, broccoli), especially from Guatemala, Mexico, Peru; travel to or residence in endemic regions (Guatemala, Peru, Nepal, Haiti, Indonesia, parts of Africa); warm/rainy season exposure — "prevalence...rises during periods of elevated rainfall and warm weather in Guatemala, Honduras, Mexico, Jordan, Nepal, and China" (search synthesis of PMC10536660). - Age: Children in endemic areas show higher susceptibility/prevalence than adults. - Immune status: HIV/AIDS and other immunocompromising conditions (transplant recipients, chemotherapy patients) markedly increase risk of severe, prolonged, and relapsing disease and of extraintestinal (biliary) involvement. - Socioeconomic: Low-income, endemic, or disease-endemic settings with poor water/sanitation infrastructure. - No confirmed genetic risk variants have been described; no GWAS hits are catalogued for cyclosporiasis susceptibility.

Protective factors: No specific genetic protective alleles known. Environmentally, thorough cooking of produce (heat, not chemical disinfection) destroys oocysts; adequate irrigation-water treatment (microfiltration, ozone, UV) reduces field contamination (FDA Cyclospora page; PMC10536660). Repeated natural exposure in endemic areas may confer partial age-related immunity (older residents of endemic areas often show milder/asymptomatic infection versus travelers/children).

Gene-environment interactions: Not established as a specific mechanistic pathway in the literature; the dominant modifiers are host immune competence (HIV, immunosuppression) interacting with environmental oocyst exposure dose/frequency, rather than a defined host genetic polymorphism.

3. Phenotypes

Phenotype Type HPO term (suggested) Notes/Frequency
Watery diarrhea Symptom HP:0002014 (Diarrhea) Hallmark; profuse, often explosive
Abdominal cramping/pain Symptom HP:0002027 (Abdominal pain) Common
Nausea Symptom HP:0002018 (Nausea) Common
Vomiting Symptom HP:0002013 (Vomiting) Occasional
Anorexia/loss of appetite Symptom HP:0002039 (Poor appetite) Common, notable
Weight loss Sign HP:0001824 (Weight loss) Can exceed 20 lb untreated
Fatigue Symptom HP:0012378 (Fatigue) Prominent, often disproportionate
Low-grade fever Sign HP:0025336 (Low-grade fever) / HP:0001945 (Fever) Less common than diarrhea
Bloating/flatulence Symptom HP:0002583 (Bowel obstruction) not ideal; consider HP:0030765 (Abdominal bloating) Common
Myalgias Symptom HP:0003326 (Myalgia) Reported
Malabsorption Sign HP:0002024 (Malabsorption) Documented pathologically
Relapsing/remitting course Clinical course (course qualifier, not HP term) Symptoms wax and wane; may relapse days-weeks after apparent resolution
Guillain-Barré syndrome (rare sequela) Sign HP:0002878 (Guillain-Barré syndrome) Reported post-infectious complication
Reactive arthritis / Reiter syndrome (rare sequela) Sign HP:0100558 (Reactive arthritis, if available) Reported post-infectious complication
Acalculous cholecystitis / biliary disease Sign HP:0005375 (Cholecystitis) Reported in immunocompromised (AIDS) patients

Onset/severity: Incubation averages ~1 week (range 2 days–2+ weeks) (CDC Clinical Overview). Disease is "often mild or asymptomatic" in endemic populations but can be severe in infants, the elderly, and profoundly immunocompromised patients (PMC8471761). Untreated illness can last from several days to a month or longer, with some patients relapsing one or more times.

Quality of life impact: Chronic/relapsing diarrhea with substantial weight loss and fatigue can significantly impair daily functioning, particularly in immunocompromised or pediatric malnourished populations; explicit EQ-5D/SF-36 data specific to cyclosporiasis were not identified in the literature searched.

4. Genetic/Molecular Information

This is an infectious disease with no human causal gene — genetic material of interest belongs to the pathogen itself.

Pathogen genome: The C. cayetanensis nuclear genome is ~44 Mbp, 52% GC content, ~7,500 genes (PMC4851813, comparative genomics study). It also carries a mitochondrial genome (PMID for complete mitochondrial genome: PMC4455993/PLOS ONE 2015) and an apicoplast genome (a relict non-photosynthetic plastid; PMC5129617) — both used as multicopy targets for sensitive detection and geographic traceback.

Comparative genomics: C. cayetanensis shows "coccidia-like metabolism and invasion components but unique surface antigens," with overall genome organization and invasion machinery closely resembling Eimeria tenella, but differing in amino acid metabolism, propanoyl-CoA degradation, GPI-anchor biosynthesis, and N-glycosylation; unlike Eimeria spp., no active LTR-retrotransposons have been identified (PMC4851813).

Genotyping/molecular epidemiology tools (used for outbreak traceback rather than clinical variant calling): - Original MLST panel: five microsatellite loci (CYC3, CYC13, CYC15, CYC21, CYC22) — successful in <60% of stool specimens (search synthesis, PMC8506454). - Newer targeted amplicon deep sequencing (TADS)/targeted amplicon sequencing (TAS) schemes: six nuclear loci (Nu_CDS1–4, Nu_378, Nu_360i2) + two mitochondrial markers (Mt_MSR, Mt_Cmt) (PMID:37396378, PMC10311907, 2023; PMID:38792677, 2024 evaluation of increased genetic resolution). - Mitochondrial junction region typing: successfully typed 132/134 samples into 14 sequence types, matching epidemiologic clusters in 7/10 outbreaks (Emerging Infectious Diseases, 2019). - CDC's ensemble clustering method accounts for sexual recombination in the parasite's life cycle, achieving 90–94% sensitivity/99% specificity for 2019 outbreak clustering.

Species/lineage delineation (2023): Two nuclear loci (CDS3, 360i2) distinguish lineage A vs. B within C. cayetanensis, and a genetically distinct Chinese isolate was elevated to a new species, C. henanensis, alongside C. ashfordi (PMC10090632).

Epigenetics, somatic/germline distinction, chromosomal abnormalities: Not applicable — this is a parasitic infection, not a heritable human genetic disease.

5. Environmental Information

  • Primary environmental vehicle: Sporulated oocysts contaminating fresh produce (basil, cilantro, raspberries, snow peas, mesclun mix, broccoli) and water. Sporulation requires days-to-weeks at 22–30°C outside the host (PMC8779055).
  • Infectious agent classification: Protozoan parasite, NCBI Taxonomy ID 88456, phylum Apicomplexa, family Eimeriidae.
  • Environmental persistence: The oocyst wall confers marked resistance to routine chemical disinfectants, including chlorine — "Cyclospora may be resistant to routine chemical disinfection methods such as those using chlorine" and "routine chemical sanitizers and household produce washes are generally ineffective against Cyclospora oocysts" (FDA Cyclospora page; search synthesis). Only heat (cooking/boiling) reliably destroys oocysts in food; water treatment via microfiltration, ozone, or UV can reduce irrigation-water contamination.
  • Seasonality: Marked seasonal peaks associated with warm, rainy periods in endemic countries (Guatemala, Honduras, Mexico, Jordan, Nepal, China) and a well-documented May–August seasonal peak in U.S. outbreaks tied to imported produce.
  • Lifestyle factors: International travel to endemic regions and dietary consumption of imported raw produce are the dominant lifestyle risk factors in non-endemic countries (e.g., U.S., Canada, Europe).

6. Mechanism / Pathophysiology

Causal chain (upstream → downstream):

  1. Ingestion of sporulated oocysts (via contaminated produce/water) →
  2. Excystation in the gut lumen: sporozoites are released from sporocysts (each sporulated oocyst contains 2 sporocysts, each with 2 elongated sporozoites) →
  3. Invasion of small intestinal (and occasionally biliary) epithelial cells: sporozoites transform into schizonts within a parasitophorous vacuole in the apical cytoplasm, above the host cell nucleus, most numerous at villus tips (PMC8779055; PMID:9395371) →
  4. Asexual schizogony (merogony):
  5. Type I meronts contain 8–12 merozoites (~3–4 µm) that perpetuate autoinfection/amplification within the host intestine.
  6. Type II meronts contain 4 merozoites (~12–15 µm) that differentiate into the sexual stages.
  7. Gametogony: Type II merozoites form microgametocytes (male, flagellated microgametes ~6.6 × 5.2 µm) and macrogametocytes (female, containing eosinophilic wall-forming bodies) →
  8. Fertilization and oocyst formation: unsporulated oocysts (8–10 µm, spheroidal) are shed in feces, non-infectious until environmental sporulation (7–14 days at 22–30°C) completes the cycle →
  9. Local tissue injury: histopathology shows acute-to-chronic inflammatory infiltration of the lamina propria (lymphocytes, plasma cells, eosinophils), surface epithelial disarray, loss of brush border, villous blunting/flattening, crypt hyperplasia, diffuse edema, and vascular dilatation in jejunal biopsies (PMID:9395371; PMC8471761) →
  10. Functional consequence: disruption of the absorptive epithelium produces malabsorptive, secretory watery diarrhea, confirmed pathologically as malabsorption in biopsy-proven cases; inflammatory changes may persist beyond parasitologic clearance, potentially explaining post-infectious relapsing symptoms.
  11. Rare post-infectious immune-mediated sequelae: Guillain-Barré syndrome and reactive arthritis/Reiter syndrome have been reported following cyclosporiasis, suggesting a molecular-mimicry or immune-activation mechanism analogous to other enteric-infection-triggered autoimmune sequelae, though the precise immunologic pathway is not well characterized in the literature reviewed.
  12. Immunocompromised host divergence: in AIDS/transplant patients, parasite burden and tissue spread (including biliary epithelium, producing acalculous cholecystitis and biliary disease) are markedly increased, and clearance requires prolonged/higher-dose antimicrobial therapy.

Cell types involved: small intestinal (jejunal) enterocytes/epithelial cells (CL:0000584 enterocyte; CL:0002250 intestinal crypt cell), biliary epithelial cells (CL:1000343 epithelial cell of intrahepatic bile duct) in immunocompromised hosts, lamina propria lymphocytes and plasma cells (CL:0000542 lymphocyte, CL:0000786 plasma cell).

Biological processes (GO terms): - GO:0044409 (entry into host) / GO:0075732 (viral penetration into host cell, N/A — better: GO:0044412 or general "invasion of host epithelial cell") - GO:0006955 (immune response) - GO:0002526 (acute inflammatory response) - GO:0022415 (viral process — N/A for parasite; use GO:0044403 symbiotic process / host-parasite interaction terms) - GO:0007586 (digestion) — disrupted - GO:0006811 (ion transport) — disrupted absorptive function underlying malabsorption

Protein dysfunction / biochemical abnormalities: Not a host-protein-defect disease; the pathogen's own invasion-related surface antigens are apicomplexan-family unique (distinct from Eimeria), a focus of ongoing genomic characterization (PMC4851813) but not yet resolved to specific therapeutic targets.

Omics/advanced technologies: No single-cell, spatial transcriptomic, or CRISPR functional-genomics datasets specific to C. cayetanensis host-response were identified — a direct consequence of the field's central research bottleneck (see Model Organisms, below): there is no cell-culture or animal model system to propagate the parasite, severely limiting mechanistic/omics studies (PMC10536660; PMC9608778 "Hastening Progress in Cyclospora Requires Studying Eimeria Surrogates").

7. Anatomical Structures Affected

  • Organ level: Primary target — small intestine (jejunum predominantly). Secondary/complication-level involvement — biliary tract (gallbladder, bile ducts) in immunocompromised hosts. Body system: digestive/gastrointestinal system; secondary neurological (Guillain-Barré) and musculoskeletal/rheumatologic (reactive arthritis) involvement as rare post-infectious sequelae.
  • UBERON terms: UBERON:0002115 (jejunum), UBERON:0002108 (small intestine), UBERON:0002110 (gallbladder), UBERON:0002394 (bile duct), UBERON:0001007 (digestive system).
  • Tissue/cell level: Intestinal epithelium (villus and crypt enterocytes), lamina propria (inflammatory infiltrate: lymphocytes, plasma cells, occasional eosinophils), biliary epithelium.
  • Cell Ontology terms: CL:0000584 (enterocyte), CL:0009017 (intestinal crypt stem cell / crypt epithelial cell), CL:1000343 (epithelial cell of intrahepatic bile duct), CL:0000542 (lymphocyte), CL:0000786 (plasma cell).
  • Subcellular level: Parasites reside within a parasitophorous vacuole in the apical cytoplasm of host epithelial cells, above the nucleus — GO Cellular Component: GO:0020009 (parasitophorous vacuole membrane) / GO:0033664 (host parasitophorous vacuole).
  • Localization: Villus tips most heavily parasitized; no clear lateralization pattern (diffuse small-bowel process).

8. Temporal Development

  • Onset: Incubation averages ~1 week (range 2 days to ≥2 weeks) after ingestion of sporulated oocysts; can affect any age but more severe in infants, elderly, and immunocompromised.
  • Onset pattern: Acute onset of watery diarrhea and systemic symptoms.
  • Progression/course: Highly variable — "some patients experience a single self-limited episode, whereas others have waxing and waning symptoms" (PMC8471761). Untreated illness may last days to a month or longer; relapsing course is characteristic, with symptoms resolving then recurring days to a week later, sometimes multiple cycles.
  • Duration: Self-limited in many immunocompetent hosts over weeks; can become chronic/relapsing in immunocompromised patients (case report of chronic Cyclospora infection with intestinal malabsorption in a heart transplant recipient, PMC12584178).
  • Remission: Both spontaneous (immunocompetent) and treatment-induced (TMP-SMX) remission occur; inflammatory changes on biopsy may outlast parasitologic cure.
  • Critical periods: No defined developmental critical window; risk of severe/prolonged disease is driven by immune status rather than age-specific biological windows (though pediatric and elderly hosts trend toward more severe presentations).

9. Inheritance and Population

Not a genetic disease — no Mendelian inheritance pattern, penetrance, expressivity, anticipation, mosaicism, founder effect, or carrier frequency applies.

Epidemiology: - Global prevalence: Pooled worldwide human prevalence estimated at 3.55% in a 2024 systematic review/meta-analysis/meta-regression (Acta Tropica, ScienceDirect, S0001706X24000597); prevalence is markedly higher in low-income/endemic countries and among individuals with diarrhea, particularly in Africa. - Geographic distribution: At least 54 countries have documented C. cayetanensis infections, with outbreaks recorded in 13; high-endemicity regions include Guatemala, Honduras, Peru, Nepal, Haiti, Indonesia, Madagascar, and parts of the Middle East/Asia (Jordan, China). - U.S. burden: In 2023, 4 of 24 (17%) major FDA-investigated foodborne outbreaks were attributed to C. cayetanensis; a June 2023 restaurant-associated outbreak in Limestone County, Alabama produced 47 cases linked to cilantro (PMC12005484; MMWR-style report). 2022 and 2024 showed similar patterns, with the majority of outbreak food-source investigations remaining inconclusive (only broccoli was conclusively confirmed in one 2023 outbreak) (NACMCF 2023 report, FSIS). - Age distribution: Children in endemic countries show higher susceptibility/prevalence than adults; in non-endemic countries, cases cluster among travelers and consumers of imported produce across all ages. - Sex ratio: No strong sex predilection reported in the literature reviewed. - Travelers: C. cayetanensis is a recognized cause of traveler's diarrhea, especially among travelers returning to industrialized countries from endemic regions.

10. Diagnostics

Clinical/laboratory tests: - Microscopy: Stool ova-and-parasite exam with modified acid-fast (Kinyoun) staining — oocysts stain bright pinkish-red, though staining is variable (some mottled, some non-refractile "glassy" and unstained); modified safranin staining offers improved sensitivity and faster turnaround than modified acid-fast; UV autofluorescence microscopy — oocysts autofluoresce blue/green under UV, considered more reliable than acid-fast staining alone. - Molecular (PCR/NAAT): C. cayetanensis-specific PCR assays (e.g., PMC2493149, highly sensitive/specific PCR) and multiplex syndromic gastrointestinal panels (e.g., FilmArray GI Panel) that include Cyclospora targets are increasingly used clinically; molecular methods avoid the sporulation-dependent morphologic ambiguity of microscopy. - Biopsy: Small intestinal (jejunal) biopsy can show diagnostic intracellular parasite stages within parasitophorous vacuoles, though rarely required given stool-based diagnostics. - LOINC: relevant test panels exist for ova-and-parasite exam and GI PCR panels (specific LOINC codes for Cyclospora antigen/PCR are laboratory-specific; Mayo Clinic Labs test CYCL — "Cyclospora Stain, Feces" — is a representative clinical order).

Genetic/molecular epidemiologic testing (not for individual diagnosis but outbreak investigation): targeted amplicon sequencing (TAS/TADS) genotyping panels (nuclear + mitochondrial loci) used by CDC and public health labs for traceback (PMID:37396378; PMID:38792677).

Screening: No population-based or newborn screening programs exist (this is an acute infectious, not congenital/genetic, disease); case-based surveillance and outbreak cluster detection (via PulseNet-style genotyping) function as the "screening" analog at the public-health level.

Differential diagnosis: Other causes of infectious watery diarrhea/traveler's diarrhea — Cryptosporidium, Giardia, Cystoisospora (Isospora) belli, enterotoxigenic E. coli, norovirus, and in immunocompromised hosts, microsporidiosis.

11. Outcome/Prognosis

  • Mortality: Generally low in immunocompetent hosts; cyclosporiasis is rarely fatal but can cause significant morbidity, especially in malnourished children and severely immunocompromised patients where prolonged, high-volume diarrhea and malabsorption can be life-threatening ("prolonged diarrhea that could be life threatening in immunocompromised patients," search synthesis of clinical reviews).
  • Morbidity: Significant weight loss (reportedly >20 lb in some untreated cases), fatigue, and malabsorption; chronic cases in immunocompromised hosts (e.g., transplant recipients) can produce sustained intestinal malabsorption (PMC12584178 case report).
  • Recovery: Excellent with appropriate TMP-SMX treatment (>90% cure rates in immunocompetent patients per PMC8471761); without treatment, illness resolves over days to a month (occasionally longer) but relapse is common.
  • Complications: Acalculous cholecystitis/biliary disease (especially AIDS patients), Guillain-Barré syndrome, reactive arthritis/Reiter syndrome as rare post-infectious sequelae.
  • Prognostic factors: Immune status is the dominant prognostic determinant — HIV/AIDS, transplant immunosuppression, and extremes of age (infancy, elderly) predict more severe/prolonged/relapsing disease and treatment courses of longer duration or need for secondary prophylaxis.

12. Treatment

Pharmacotherapy (first-line): - Trimethoprim-sulfamethoxazole (TMP-SMX): treatment of choice. Standard adult regimen: one double-strength tablet (TMP 160 mg/SMX 800 mg) orally twice daily for 7–10 days, achieving >90% cure rates in immunocompetent patients (PMC8471761). In a randomized controlled trial in HIV-infected patients, diarrhea ceased in all 19 TMP-SMX-treated patients, with 18/19 (95%) stool-negative by day 7 (PMID:10836915, comparing TMP-SMX vs. ciprofloxacin for Isospora belli and C. cayetanensis in HIV). - HIV-infected/immunocompromised patients: may require longer treatment courses and, in some cases, secondary (chronic suppressive) prophylaxis to prevent relapse. - Alternatives for sulfa allergy: Ciprofloxacin (less effective than TMP-SMX but an acceptable alternative) and nitazoxanide are used when TMP-SMX cannot be tolerated, though treatment failures are more common with these agents; "no highly effective alternatives have been identified for persons who are allergic to or intolerant of TMP-SMX."

MAXO terms: - MAXO:0000647 (chemotherapy) — not applicable; better: generic pharmacotherapy term - Use treatment_term: NCIT:C15986 (Pharmacotherapy) with therapeutic_agent: CHEBI term for trimethoprim/sulfamethoxazole combination (CHEBI:45924 co-trimoxazole), or individual components CHEBI:45963 (trimethoprim), CHEBI:9328 (sulfamethoxazole); ciprofloxacin — CHEBI:100241; nitazoxanide — CHEBI:7580. - MAXO:0000950 (supportive care) for oral rehydration/fluid-electrolyte management.

Advanced therapeutics: None applicable — no gene therapy, cell therapy, RNA-based therapy, targeted therapy, or immunotherapy is used or in development for this parasitic infection.

Surgical/interventional: Not typically required except for management of complications (e.g., cholecystectomy in rare severe acalculous cholecystitis cases).

Supportive care: Oral or IV rehydration and electrolyte repletion for volume losses, nutritional support for malabsorption/weight loss.

Experimental treatments: No dedicated Cyclospora-specific clinical trials were identified as currently active (search of trial-focused sources returned no Cyclospora-specific NCT-registered interventional trials); most evidence base derives from older HIV-era comparative drug trials (e.g., PMID:10836915).

Treatment algorithm: Confirm diagnosis (stool microscopy/PCR) → first-line TMP-SMX 7–10 days → reassess for immunocompromised status (consider extended course/secondary prophylaxis) → for sulfa allergy, ciprofloxacin or nitazoxanide as second-line with counseling on lower efficacy.

13. Prevention

  • Primary prevention: No vaccine exists. Key strategies: (1) thorough cooking of high-risk imported produce (only heat reliably destroys oocysts, since chlorine and standard produce washes are largely ineffective against the resistant oocyst wall); (2) safe drinking-water practices, especially for travelers to endemic regions; (3) improved agricultural practices — sanitized irrigation water, water treatment via microfiltration/ozone/UV in growing regions (FDA; PMC10536660).
  • Secondary prevention (screening/early detection): No population screening program exists; clinical suspicion in returning travelers or after implicated produce exposure prompts stool testing; outbreak surveillance and genotyping-based traceback (CDC's TAS/mitochondrial-junction methods) functions as public-health-level early detection to halt ongoing exposures.
  • Tertiary prevention: Prompt TMP-SMX treatment to prevent complications (biliary disease, prolonged malabsorption) and, in immunocompromised patients, secondary prophylaxis to prevent relapse.
  • Public health interventions: FDA/CDC foodborne-outbreak investigation infrastructure (PulseNet-style genotype clustering), import controls/testing on high-risk produce commodities from endemic-growing regions, and grower-level Good Agricultural Practices (GAP) guidance (2023 NACMCF report on Cyclospora in produce).
  • Traveler's health counseling: Avoid unpeeled/unwashed raw produce and untreated water in endemic destinations.
  • Genetic counseling: Not applicable (non-genetic disease).

14. Other Species / Natural Disease

  • Host range: Humans are the only known definitive host for C. cayetanensis sensu stricto; extensive experimental attempts to infect a wide variety of animal models (including non-human primates) have failed (PMC8779055; PMC10536660).
  • Related organisms in animals: Numerous other Cyclospora species infect non-human hosts (reptiles, rodents, other mammals) but do not cause human disease; a molecular survey found Cyclospora spp. in cattle in Shanxi Province, China (PMC11274234), raising open questions about environmental/zoonotic overlap that remain unresolved for human-infective genotypes specifically.
  • Newly named species (2023): Cyclospora ashfordi sp. nov. and Cyclospora henanensis sp. nov., both shown to cause human cyclosporiasis alongside classic C. cayetanensis lineages A/B (PMC10090632) — an important taxonomic/comparative-biology update.
  • Transmission/zoonotic potential: No confirmed zoonotic transmission cycle for the human-infective Cyclospora species/lineages; the human-only host cycle is a key epidemiologic feature distinguishing cyclosporiasis from cryptosporidiosis (which does have zoonotic reservoirs).
  • Comparative biology: Genomically and morphologically, C. cayetanensis is closely allied with Eimeria (94–98% SSU rRNA sequence similarity), particularly avian-infecting Eimeria species, and shares coccidia-like metabolic and invasion machinery with Eimeria tenella despite unique surface antigens (PMC4851813).

15. Model Organisms

This is the single greatest research bottleneck for the disease:

  • No validated animal model exists. "Researchers have been unable to establish C. cayetanensis infection in a wide variety of animal models," and there is no in vitro/tissue-culture propagation system either (PMC10536660; PMC9608778).
  • Human challenge study: A CDC pilot human-challenge study (PMID:15200870, Emerging Infectious Diseases 2004) dosed 7 healthy volunteers with 200–49,000 oocysts; none developed clinical or parasitologic evidence of infection over 16 weeks of follow-up — underscoring major unknowns in infectious dose, host susceptibility factors, and possibly reduced oocyst viability by the time of the challenge inoculum.
  • Surrogate model strategy: Given the impasse, researchers have proposed using the genomically and biologically related genus Eimeria (which does have established animal infection models, e.g., E. tenella in chickens, E. falciformis in mice) as a tractable surrogate system to model coccidian biology relevant to Cyclospora — see PMC9608778, "Hastening Progress in Cyclospora Requires Studying Eimeria Surrogates."
  • Available research material: Investigators must rely entirely on oocysts recovered from naturally infected human stool specimens, which are scarce, variably viable, and logistically difficult to standardize — severely constraining functional genomics, drug-screening, vaccine development, and mechanistic host-response studies.
  • Resources: No dedicated Cyclospora model-organism repository/database exists analogous to MGI/ZFIN/FlyBase for this pathogen; genomic resources are housed in general databases (NCBI Taxonomy txid88456, GenBank genome assemblies referenced in PMC4851813, PMC4455993, PMC5129617).

Summary of Key Ontology Term Suggestions

Category Term
Disease MONDO:0005725; ICD-10-CM A07.4; DOID:12750; ORPHA210
Organism NCBITaxon:88456 (Cyclospora cayetanensis)
Phenotypes (HP) HP:0002014 Diarrhea; HP:0002027 Abdominal pain; HP:0002018 Nausea; HP:0002039 Poor appetite; HP:0001824 Weight loss; HP:0012378 Fatigue; HP:0002024 Malabsorption; HP:0002878 Guillain-Barré syndrome; HP:0005375 Cholecystitis
Cell types (CL) CL:0000584 enterocyte; CL:1000343 intrahepatic bile duct epithelial cell; CL:0000542 lymphocyte; CL:0000786 plasma cell
Anatomy (UBERON) UBERON:0002115 jejunum; UBERON:0002108 small intestine; UBERON:0002110 gallbladder; UBERON:0002394 bile duct
Chemicals (CHEBI) CHEBI:45963 trimethoprim; CHEBI:9328 sulfamethoxazole; CHEBI:100241 ciprofloxacin; CHEBI:7580 nitazoxanide
Treatment (MAXO/NCIT) NCIT:C15986 Pharmacotherapy; MAXO:0000950 supportive care

Sources