Psittacosis

name: Psittacosis
creation_date: "2026-06-28T00:00:00Z"
description: >
  Psittacosis (ornithosis, "parrot fever") is a zoonotic respiratory infection
  caused by Chlamydia (Chlamydophila) psittaci, an obligate intracellular
  bacterium transmitted to humans from birds (pet birds and poultry). After
  inhalation, the organism replicates intracellularly and produces an atypical
  pneumonia that is the predominant clinical presentation; severe cases can
  progress to acute respiratory distress syndrome and multi-organ dysfunction.
  Because the organism is intracellular, treatment requires a cell-penetrant
  antibiotic — tetracyclines (doxycycline) are first-line, with macrolides or
  fluoroquinolones as alternatives; beta-lactams are ineffective.
category: Infectious Disease
parents:
- Bacterial Respiratory Infection
synonyms:
- Ornithosis
- Parrot fever
- Chlamydia psittaci infection
disease_term:
  preferred_term: psittacosis
  term:
    id: MONDO:0005888
    label: ornithosis
pathophysiology:
- name: Inhalation and Obligate Intracellular Chlamydial Infection
  role: trigger
  conforms_to: "intracellular_pathogen_persistence#Intracellular Niche and Beta-Lactam Exclusion"
  description: >
    Psittacosis follows inhalation of aerosols from infected birds. Chlamydia
    psittaci is an obligate intracellular bacterium that replicates within host
    cells, an intracellular lifestyle that underlies the requirement for
    cell-penetrant antibiotics, because beta-lactams cannot reach the intracellular
    organism.
  cell_types:
  - preferred_term: respiratory epithelial cell
    term:
      id: CL:0002632
      label: epithelial cell of lower respiratory tract
  biological_processes:
  - preferred_term: symbiont entry into host cell
    term:
      id: GO:0046718
      label: symbiont entry into host cell
  - preferred_term: biological process involved in interaction with host
    term:
      id: GO:0051701
      label: biological process involved in interaction with host
  evidence:
  - reference: PMID:15895932
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Chlamydia are obligate intracellular bacteria.
    explanation: >-
      Establishes Chlamydia (including C. psittaci) as obligate intracellular
      bacteria, the basis for the intracellular-niche conformance. Evidence source
      is OTHER as this is a review article.
  - reference: PMID:15895932
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Chlamydophila psittaci causes psittacosis, a severe zoonotic pneumonia
      transmitted by birds.
    explanation: >-
      Identifies C. psittaci as the cause of psittacosis, a zoonotic pneumonia
      transmitted by birds. Evidence source is OTHER as this is a review article.
  downstream:
  - target: Atypical Pneumonia and Systemic Illness
    description: >-
      Intracellular replication produces an atypical pneumonia that can become
      severe and multisystem.
  - target: Chlamydial Ribosomal Translation (Tetracycline Target)
    description: >-
      The organism's ribosome is the molecular target of tetracycline therapy.

- name: Atypical Pneumonia and Systemic Illness
  role: consequence
  description: >
    Pneumonia is the predominant clinical presentation of psittacosis; severe cases
    can progress to acute respiratory distress syndrome and multi-organ
    dysfunction.
  biological_processes:
  - preferred_term: inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
    modifier: INCREASED
  locations:
  - preferred_term: lung
    term:
      id: UBERON:0002048
      label: lung
  evidence:
  - reference: PMID:42255501
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Pneumonia was the predominant clinical presentation, and severe cases could
      progress to acute respiratory distress syndrome and multi-organ dysfunction.
    explanation: >-
      Scoping review establishing pneumonia as the predominant presentation, with
      progression to ARDS and multi-organ dysfunction in severe cases. Evidence
      source is OTHER as this is a review article.
  downstream: []

- name: Chlamydial Ribosomal Translation (Tetracycline Target)
  role: therapeutic_vulnerability
  conforms_to: "bacterial_protein_synthesis_inhibition#Bacterial mRNA Translation by the Ribosome"
  description: >
    C. psittaci depends on its bacterial ribosome for protein synthesis. Doxycycline,
    a tetracycline with good intracellular bioavailability, binds the 30S ribosomal
    subunit and arrests bacterial protein synthesis — combining the ribosomal target
    with the intracellular penetration needed to reach the organism, which is why a
    tetracycline rather than a beta-lactam is first-line.
  biological_processes:
  - preferred_term: translation
    term:
      id: GO:0006412
      label: translation
  evidence:
  - reference: PMID:24336183
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The ribosome is one of the main antibiotic targets in the bacterial cell.
    explanation: >-
      Establishes the bacterial ribosome as the target of tetracyclines and other
      protein-synthesis inhibitors, the step this node represents. Evidence source
      is OTHER as this is a review article.
  downstream: []
phenotypes:
- category: Respiratory
  name: Pneumonia
  description: >
    Atypical pneumonia is the predominant manifestation of psittacosis.
  phenotype_term:
    preferred_term: Pneumonia
    term:
      id: HP:0002090
      label: Pneumonia
  evidence:
  - reference: PMID:42255501
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Pneumonia was the predominant clinical presentation, and severe cases could
      progress to acute respiratory distress syndrome and multi-organ dysfunction.
    explanation: >-
      Pneumonia is the predominant clinical presentation of psittacosis. Evidence
      source is OTHER as this is a review article.
- category: Constitutional
  name: Fever
  description: >
    Fever is characteristic (psittacosis is also called "parrot fever").
  phenotype_term:
    preferred_term: Fever
    term:
      id: HP:0001945
      label: Fever
- category: Respiratory
  name: Cough
  description: >
    Cough accompanies the atypical pneumonia of psittacosis.
  phenotype_term:
    preferred_term: Cough
    term:
      id: HP:0012735
      label: Cough
- category: Respiratory
  name: Dyspnea
  description: >
    Shortness of breath occurs, and severe disease can progress to respiratory
    failure/ARDS.
  phenotype_term:
    preferred_term: Dyspnea
    term:
      id: HP:0002094
      label: Dyspnea
treatments:
- name: Doxycycline
  description: >
    Tetracycline antibiotic with good intracellular bioavailability that inhibits
    bacterial protein synthesis at the 30S ribosome; first-line treatment for
    psittacosis because it reaches the intracellular organism. Macrolides and
    fluoroquinolones are alternatives.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: doxycycline
      term:
        id: CHEBI:50845
        label: doxycycline
  target_mechanisms:
  - target: Chlamydial Ribosomal Translation (Tetracycline Target)
    treatment_effect: INHIBITS
    description: >-
      Doxycycline binds the 30S ribosome and arrests C. psittaci protein synthesis.
  - target: Inhalation and Obligate Intracellular Chlamydial Infection
    treatment_effect: INHIBITS
    description: >-
      Doxycycline's intracellular bioavailability lets it reach the intracellular
      organism that beta-lactams cannot.
  evidence:
  - reference: PMID:15895932
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Treatment should use an antibiotic with good intracellular bioavailability
      such as tetracycline, macrolides and new generation fluoroquinolones.
    explanation: >-
      Supports use of cell-penetrant antibiotics (tetracycline first-line) for
      intracellular chlamydial infection. Evidence source is OTHER as this is a
      review article.
notes: >
  Created as part of the Respiratory Infections project. Intracellular zoonotic
  atypical pneumonia (bird reservoir); conforms to the
  intracellular_pathogen_persistence module (intracellular niche) and the
  bacterial_protein_synthesis_inhibition module (tetracycline ribosomal target),
  mirroring the Q_Fever and Murine_Typhus doxycycline pattern. disease_term uses
  MONDO:0005888 (ornithosis, the MONDO label for psittacosis). The infectious_agent
  (NCBITaxon) block was omitted at creation and C. psittaci is described in text.