Hepatitis A

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Discussions and Knowledge Gaps

1

How does adaptive immunity produce the liver injury of hepatitis A, as distinct from clearing the virus - and why does HAV never persist?

KNOWLEDGE GAP hav_immunopathogenesis_unsettled

Attached to

pathophysiology#Acute Hepatic Inflammatory Reaction pathophysiology#Host-Factor-Dependent Severity Modulation

This entry asserts that severity is host-determined, and annotates the inflammatory node with adaptive immunity accordingly, but the mechanism connecting the two is not settled. The review literature states plainly that how HAV is so effectively controlled by B and T cell immunity, and why it lacks the propensity to persist that HBV and HCV have, cannot yet be adequately explained, and that recent work challenges long-held concepts of how antibodies and T cells contribute to pathogenesis. The entry therefore deliberately stops short of curating a specific cytotoxic effector mechanism: naming CD8 or NK-mediated killing as the cause of hepatocyte injury would assert more than the cited evidence supports.

Proposed experiments

Intrahepatic immune profiling across the age-severity gradient

hav_intrahepatic_immune_profiling

Comparing intrahepatic T cell, NK cell and antibody responses between asymptomatic infected children and symptomatic infected adults in the same outbreak would test directly whether the age-dependent severity this entry models is produced by the adaptive response, and identify which effector arm causes the injury.

⚙

Pathophysiology

5

Faecal-Oral Acquisition and Hepatocyte Infection

Ingested HAV reaches the liver and replicates in hepatocytes. The virus is shed back into bile and stool, sustaining faecal-oral transmission. Peak shedding and infectivity precede the onset of jaundice by roughly two weeks, so transmission is largely presymptomatic.

hepatocyte CL:0000182

liver UBERON:0002107

Downstream

Acute Hepatic Inflammatory Reaction Infection of hepatocytes provokes an acute inflammatory response in the liver.

Show evidence (1 reference)

PMID:32389358 SUPPORT Other

"Hepatitis A virus (HAV) is a positive-strand RNA virus that is transmitted feco-orally through person-to-person contact."

Establishes the acquisition route that initiates this node. Evidence source is OTHER because this is a clinical review.

Acute Hepatic Inflammatory Reaction

HAV infection produces an acute inflammatory reaction in the liver, with hepatocellular injury reflected in raised transaminases and, when severe enough, jaundice and hyperbilirubinaemia. This is the central node of the disease and it is self-limiting in the great majority of cases. Whether it is clinically apparent at all depends on host factors rather than on viral ones - which is why the same infection is silent in a child and overt in an adult. B and T cell immunity is what controls the infection, and the injury is understood to be substantially immune-mediated rather than a direct cytopathic effect of the virus - but see the attached KNOWLEDGE_GAP: how adaptive immunity produces the liver injury, as distinct from clearing the virus, is not settled.

hepatocyte CL:0000182 T cell CL:0000084 B cell CL:0000236

inflammatory response GO:0006954 ↑ INCREASED adaptive immune response GO:0002250

liver UBERON:0002107

Downstream

Jaundice Acute inflammatory liver injury impairs bilirubin handling enough to produce icterus in symptomatic infections.

Constitutional Prodrome The acute HAV inflammatory response produces the fever and malaise that precede jaundice in clinically apparent disease.

Dark Urine Cholestatic bilirubin accumulation during the acute inflammatory illness is excreted in urine, producing dark urine before or alongside jaundice.

Host-Factor-Dependent Severity Modulation Host immunological status, age, pregnancy, and pre-existing liver disease determine how severe the inflammatory reaction becomes.

Spontaneous Resolution and Lifelong Immunity In most people the inflammatory reaction resolves and leaves protective anti-HAV IgG.

Show evidence (3 references)

PMID:37770459 SUPPORT Other

"HAV causes an acute inflammatory reaction in the liver that usually resolves spontaneously without chronic sequelae."

States both the nature of this node and its usual outcome, including the absence of chronic sequelae that distinguishes HAV from the other hepatotropic viruses. Evidence source is OTHER because this is a review.

PMID:32389358 SUPPORT Other

"Infection is often asymptomatic in children, but adults present with jaundice, abdominal pain, hepatitis, and hyperbilirubinemia."

Documents the age-dependent clinical expression of this node. Evidence source is OTHER because this is a clinical review.

PMID:29844218 SUPPORT Other

"The objective of this review is to summarize our understanding of the relationship between patterns of virus replication, adaptive immune responses, and acute liver injury in HAV and HEV infections."

Establishes that acute liver injury in hepatitis A is understood in terms of the adaptive immune response rather than viral replication alone, which is the basis for annotating this node with adaptive immunity and its effector cells. Evidence source is OTHER because this is a review.

Host-Factor-Dependent Severity Modulation

The severity of hepatitis A is set by the host, not by viral genotype. Immunological status, age, pregnancy, and underlying liver disease all modify the outcome, which is why universal childhood vaccination in intermediate-endemicity settings and targeted vaccination of people with chronic liver disease are both rational strategies. Paradoxically, improvements in sanitation that delay the age of first exposure increase the burden of symptomatic disease.

Downstream

Prolonged, Relapsing, or Fulminant Course Unfavourable host factors shift the acute reaction toward a prolonged, relapsing, or fulminant course.

Show evidence (1 reference)

PMID:37770459 SUPPORT Other

"Host factors, such as immunological status, age, pregnancy and underlying hepatic diseases, can affect the severity of disease."

Names the host variables that modulate this node, the basis for risk-targeted vaccination. Evidence source is OTHER because this is a review.

Prolonged, Relapsing, or Fulminant Course

A minority of patients depart from the usual self-limited course. Up to 20% have a prolonged or relapsing illness, and fewer than 1% develop acute liver failure. Acute liver failure is the mechanism of death in hepatitis A; because no antiviral exists, management is supportive and, in the most severe cases, transplantation.

Downstream

Acute Liver Failure Fulminant severe HAV courses cross the threshold into acute liver failure, the life-threatening complication documented in fewer than 1% of cases.

Show evidence (1 reference)

PMID:37770459 SUPPORT Other

"However, up to 20% of patients experience a prolonged or relapsed course and <1% experience acute liver failure."

Quantifies both departures from the usual course. Evidence source is OTHER because this is a review.

Spontaneous Resolution and Lifelong Immunity

In the great majority of cases the infection resolves without treatment and without chronic sequelae. Anti-HAV IgG produced in response to infection persists for life and protects against re-infection; vaccine-induced antibody confers long-term protection by the same mechanism. This node is the reason hepatitis A has no chronic arm at all - there is no persistent reservoir, no cirrhosis pathway, and no virus-driven hepatocellular carcinoma.

Show evidence (2 references)

PMID:37770459 SUPPORT Other

"Anti-HAV IgG antibodies produced in response to HAV infection persist for life and protect against re-infection; vaccine-induced antibodies against hepatitis A confer long-term protection."

Establishes lifelong humoral immunity after both natural infection and vaccination. Evidence source is OTHER because this is a review.

PMID:34652109 SUPPORT Other

"The disease is usually self-limited, supportive care is often sufficient for treatment, and chronic infection or chronic liver disease does not occur."

States explicitly that chronic infection does not occur, the guardrail that keeps this entry from being curated with a chronic arm. Evidence source is OTHER because this is a clinical review.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

4

Digestive 2

Jaundice HP:0000952

Show evidence (1 reference)

PMID:32389358 SUPPORT Other

"Infection is often asymptomatic in children, but adults present with jaundice, abdominal pain, hepatitis, and hyperbilirubinemia."

Documents jaundice as a presenting feature in adults. Evidence source is OTHER because this is a clinical review.

Acute Liver Failure VERY_RARE Acute hepatic failure HP:0006554

Show evidence (1 reference)

PMID:37770459 SUPPORT Other

"However, up to 20% of patients experience a prolonged or relapsed course and <1% experience acute liver failure."

Provides the frequency of acute liver failure recorded here as VERY_RARE (<1%). Evidence source is OTHER because this is a review.

Genitourinary 1

Dark Urine HP:0040319

Show evidence (1 reference)

PMID:34652109 SUPPORT Other

"Classic symptoms include fever, malaise, dark urine, and jaundice and are more common in older children and adults."

Documents dark urine among the classic presenting features. Evidence source is OTHER because this is a clinical review.

Metabolism 1

Constitutional Prodrome Fever HP:0001945

Show evidence (1 reference)

PMID:34652109 SUPPORT Other

"Classic symptoms include fever, malaise, dark urine, and jaundice and are more common in older children and adults."

Lists the prodromal symptoms and their age distribution. Evidence source is OTHER because this is a clinical review.

💊

Medical Actions

2

Supportive Care

Action: Supportive Care NCIT:C15747

Platform: Other

There is no specific antiviral therapy for hepatitis A. Because the disease is self-limited in almost all patients, supportive care is sufficient; management is escalated only for the small minority developing acute liver failure.

Show evidence (1 reference)

PMID:34652109 SUPPORT Other

"The disease is usually self-limited, supportive care is often sufficient for treatment, and chronic infection or chronic liver disease does not occur."

Establishes supportive care as sufficient treatment for the usual course. Evidence source is OTHER because this is a clinical review.

Hepatitis A Vaccination

Action: Vaccination NCIT:C15346

Platform: Vaccine

Inactivated hepatitis A vaccine is the mainstay of prevention and works by inducing the same lifelong protective antibody that natural infection produces. It is used both for routine childhood immunisation and for pre-exposure and post-exposure prophylaxis; immune globulin substitutes when the vaccine is contraindicated or the recipient is too young. Programme-level deployment has measurably reduced HAV incidence.

Mechanism Target:

INHIBITS Faecal-Oral Acquisition and Hepatocyte Infection — Vaccine-induced anti-HAV antibody neutralises the virus before hepatocyte infection is established, preventing the whole downstream chain rather than modifying it.

Show evidence (1 reference)

PMID:37770459 SUPPORT Other

"To date, >25 countries worldwide have implemented such programmes, resulting in a reduction in the incidence of HAV infection."

Provides population-level evidence that vaccination prevents infection rather than merely attenuating disease. Evidence source is OTHER because this is a review summarising national programme outcomes.

Show evidence (2 references)

PMID:32389358 SUPPORT Other

"Vaccination is the mainstay of prevention and should be given before exposure whenever possible."

States the role of vaccination in prevention. Evidence source is OTHER because this is a clinical review.

PMID:34652109 SUPPORT Other

"The vaccine is usually recommended for pre- and postexposure prophylaxis, but immune globulin can be used in patients who are too young to be vaccinated or if the vaccine is contraindicated."

Documents the pre- and post-exposure indications and the immune globulin alternative. Evidence source is OTHER because this is a clinical review.

🔬

Diagnosis

1

Anti-HAV IgM Serology

Acute hepatitis A is diagnosed by detecting IgM antibodies against HAV. Anti-HAV IgG, in contrast, marks past infection or vaccination and confers protection rather than indicating current disease.

Show evidence (1 reference)

PMID:34652109 SUPPORT Other

"Diagnosis of acute infection requires the use of serologic testing for immunoglobulin M anti-hepatitis A antibodies."

States the diagnostic test for acute infection. Evidence source is OTHER because this is a clinical review.

📈

Progression

5

Incubation

Incubation: 15-50 days

Mean incubation about 28-30 days (range 15-50 days). Virions are shed in stool and detectable in blood before symptoms begin, so infectivity peaks before jaundice appears.

Show evidence (2 references)

PMID:28534888 SUPPORT Other

"The mean incubation period is 28 days (range: 15-50)."

States the mean and the range of the incubation period.

PMID:1335649 SUPPORT Other

"The mean incubation period is approximately 30 days."

Independent review giving the mean incubation period.

Prodromal (pre-icteric) phase

Duration: A few days to a week before jaundice

Fever, malaise, nausea, vomiting and anorexia begin about a month after exposure, and aminotransferases rise during this period. The prodrome is common in adults and uncommon in children, whose infections are usually asymptomatic.

Show evidence (2 references)

PMID:32389358 SUPPORT Other

"Prodromal symptoms occur about a month following exposure and can consist of fever, malaise, nausea, vomiting, and anorexia."

Times the prodrome and lists its symptoms.

PMID:1335649 SUPPORT Other

"The onset of hepatitis A is often abrupt and characteristic prodromal symptoms are followed, within a few days to a week, by dark urine and jaundice."

Gives the duration of the prodrome before jaundice appears.

Icteric phase

Duration: Jaundice usually under 2 weeks; biochemical peak 7-10 days after its onset

Dark urine and jaundice follow the prodrome, with hyperbilirubinaemia peaking 7 to 10 days after jaundice appears; jaundice persists for under two weeks in about 85% of cases.

Show evidence (2 references)

PMID:32389358 SUPPORT Other

"Adult infections will typically also be characterized by jaundice, diarrhea, and hyperbilirubinemia, peaking 7 to 10 days after the onset of jaundice."

Times the biochemical peak of the icteric phase.

PMID:1335649 SUPPORT Other

"Nonetheless, the period of jaundice persists for < 2 weeks in approximately 85% of cases."

Gives the usual duration of jaundice.

Convalescence

Duration: Up to about 6 months to full biochemical recovery

Jaundice resolves faster than malaise and anorexia, which can last for months; nearly all adults recover completely, with normal bilirubin and aminotransferases by 6 months. HAV never establishes chronic infection or chronic liver disease, so there is no chronic phase to list.

Show evidence (3 references)

PMID:32389358 SUPPORT Other

"Jaundice will typically resolve much faster than the malaise and anorexia, which can last for months."

Describes the convalescent course of the constitutional symptoms.

PMID:1335649 SUPPORT Other

"Nearly all adult patients with clinically apparent disease experience complete clinical recovery with restoration of normal serum bilirubin and aminotransferase values by 6 months."

Gives the time to complete clinical and biochemical recovery.

PMID:34652109 SUPPORT Other

"The disease is usually self-limited, supportive care is often sufficient for treatment, and chronic infection or chronic liver disease does not occur."

Supports the absence of any chronic phase.

Relapsing or prolonged cholestatic course (variant)

Duration: Relapse within 6 months of the index illness; cholestasis up to 1 year

A recognised variant course rather than a stage every patient passes through. A prolonged or relapsing illness is reported in up to 20% of patients in one review and described as infrequent in others; relapse brings recurrent symptoms, renewed faecal HAV shedding and raised transaminases, typically within 6 months, and prolonged cholestasis has been reported for up to a year. Recovery remains the rule even in these cases, and chronic hepatitis does not follow.

Show evidence (4 references)

PMID:37770459 SUPPORT Other

"However, up to 20% of patients experience a prolonged or relapsed course and <1% experience acute liver failure."

Quantifies the prolonged or relapsing course.

PMID:32389358 SUPPORT Other

"A relapsing hepatitis is infrequently seen in adult infections with recurrent symptoms typically occurring within 6 months of prior infection."

Times the relapsing course.

PMID:32389358 SUPPORT Other

"Hepatitis A–associated prolonged cholestasis has also been reported after infection, for periods up to 1 year."

Gives the duration of the prolonged cholestatic variant.

+ 1 more reference

🦠

Infectious Agent

1

Hepatitis A virus (HAV)

A small, non-enveloped positive-strand RNA virus of the family Picornaviridae (genus Hepatovirus). It is acid- and heat-stable, which underlies its persistence in the environment and its transmission through contaminated food and water.

Hepatovirus A NCBITaxon:12092

Show evidence (1 reference)

PMID:32389358 SUPPORT Other

"Hepatitis A virus (HAV) is a positive-strand RNA virus that is transmitted feco-orally through person-to-person contact."

Identifies the agent's genome type and principal transmission route. Evidence source is OTHER because this is a clinical review.

↔️

Transmission

1

Faecal-Oral Transmission

Spread person-to-person by the faecal-oral route, and through food or water contaminated with faeces. Outbreaks cluster where sanitation is poor or populations are crowded. Infectivity peaks around the two weeks before jaundice appears, which is why outbreak control depends on rapid case identification rather than on isolating symptomatic people.

Show evidence (2 references)

PMID:32389358 SUPPORT Other

"Outbreaks are often linked to poor sanitation, overcrowding, or food and water contamination."

Documents the settings in which faecal-oral transmission produces outbreaks. Evidence source is OTHER because this is a clinical review.

PMID:34652109 SUPPORT Other

"People are most infectious 14 days before and seven days after the development of jaundice."

Establishes the infectious window relative to symptom onset, which is what makes presymptomatic spread the dominant transmission mode. Evidence source is OTHER because this is a clinical review.

{ }

Source YAML

click to show

name: Hepatitis A
creation_date: "2026-08-22T00:00:00Z"
category: Infectious Disease
description: >-
  An acute, vaccine-preventable liver infection caused by hepatitis A virus
  (HAV), a positive-strand RNA picornavirus transmitted by the faecal-oral
  route through person-to-person contact and contaminated food or water. HAV
  causes an acute inflammatory reaction in the liver that in most people
  resolves spontaneously and leaves lifelong immunity. Critically, and unlike
  hepatitis B, C, D, and E, HAV never establishes chronic infection or chronic
  liver disease - the disease is either resolved or, rarely, fatal. Severity
  rises sharply with age at infection: children are usually asymptomatic while
  adults present with jaundice, abdominal pain, and hyperbilirubinaemia. Up to
  20% of patients have a prolonged or relapsing course and fewer than 1% develop
  acute liver failure. There is no specific antiviral treatment; care is
  supportive, and vaccination is the mainstay of control.
disease_term:
  preferred_term: hepatitis A virus infection
  term:
    id: MONDO:0005790
    label: hepatitis A virus infection
parents:
- Liver Disease
- Viral Hepatitis
infectious_agent:
- name: Hepatitis A virus (HAV)
  description: >-
    A small, non-enveloped positive-strand RNA virus of the family
    Picornaviridae (genus Hepatovirus). It is acid- and heat-stable, which
    underlies its persistence in the environment and its transmission through
    contaminated food and water.
  infectious_agent_term:
    preferred_term: Hepatovirus A
    term:
      id: NCBITaxon:12092
      label: Hepatovirus A
  evidence:
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Hepatitis A virus (HAV) is a positive-strand RNA virus that is transmitted
      feco-orally through person-to-person contact.
    explanation: >-
      Identifies the agent's genome type and principal transmission route.
      Evidence source is OTHER because this is a clinical review.
transmission:
- name: Faecal-Oral Transmission
  description: >-
    Spread person-to-person by the faecal-oral route, and through food or water
    contaminated with faeces. Outbreaks cluster where sanitation is poor or
    populations are crowded. Infectivity peaks around the two weeks before
    jaundice appears, which is why outbreak control depends on rapid case
    identification rather than on isolating symptomatic people.
  evidence:
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Outbreaks are often linked to poor sanitation, overcrowding, or food and
      water contamination.
    explanation: >-
      Documents the settings in which faecal-oral transmission produces
      outbreaks. Evidence source is OTHER because this is a clinical review.
  - reference: PMID:34652109
    reference_title: "Hepatitis A."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      People are most infectious 14 days before and seven days after the
      development of jaundice.
    explanation: >-
      Establishes the infectious window relative to symptom onset, which is what
      makes presymptomatic spread the dominant transmission mode. Evidence
      source is OTHER because this is a clinical review.
pathophysiology:
- name: Faecal-Oral Acquisition and Hepatocyte Infection
  description: >-
    Ingested HAV reaches the liver and replicates in hepatocytes. The virus is
    shed back into bile and stool, sustaining faecal-oral transmission. Peak
    shedding and infectivity precede the onset of jaundice by roughly two weeks,
    so transmission is largely presymptomatic.
  role: trigger
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Hepatitis A virus (HAV) is a positive-strand RNA virus that is transmitted
      feco-orally through person-to-person contact.
    explanation: >-
      Establishes the acquisition route that initiates this node. Evidence
      source is OTHER because this is a clinical review.
  downstream:
  - target: Acute Hepatic Inflammatory Reaction
    causal_link_type: DIRECT
    description: >-
      Infection of hepatocytes provokes an acute inflammatory response in the
      liver.

- name: Acute Hepatic Inflammatory Reaction
  description: >-
    HAV infection produces an acute inflammatory reaction in the liver, with
    hepatocellular injury reflected in raised transaminases and, when severe
    enough, jaundice and hyperbilirubinaemia. This is the central node of the
    disease and it is self-limiting in the great majority of cases. Whether it
    is clinically apparent at all depends on host factors rather than on viral
    ones - which is why the same infection is silent in a child and overt in an
    adult. B and T cell immunity is what controls the infection, and the injury
    is understood to be substantially immune-mediated rather than a direct
    cytopathic effect of the virus - but see the attached KNOWLEDGE_GAP: how
    adaptive immunity produces the liver injury, as distinct from clearing the
    virus, is not settled.
  role: central_effector
  biological_scale: TISSUE
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  - preferred_term: T cell
    term:
      id: CL:0000084
      label: T cell
  - preferred_term: B cell
    term:
      id: CL:0000236
      label: B cell
  biological_processes:
  - preferred_term: inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
    modifier: INCREASED
  - preferred_term: adaptive immune response
    term:
      id: GO:0002250
      label: adaptive immune response
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:37770459
    reference_title: "Hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      HAV causes an acute inflammatory reaction in the liver that usually
      resolves spontaneously without chronic sequelae.
    explanation: >-
      States both the nature of this node and its usual outcome, including the
      absence of chronic sequelae that distinguishes HAV from the other
      hepatotropic viruses. Evidence source is OTHER because this is a review.
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Infection is often asymptomatic in children, but adults present with
      jaundice, abdominal pain, hepatitis, and hyperbilirubinemia.
    explanation: >-
      Documents the age-dependent clinical expression of this node. Evidence
      source is OTHER because this is a clinical review.
  - reference: PMID:29844218
    reference_title: "Adaptive Immune Responses in Hepatitis A Virus and Hepatitis E Virus Infections."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The objective of this review is to summarize our understanding of the
      relationship between patterns of virus replication, adaptive immune
      responses, and acute liver injury in HAV and HEV infections.
    explanation: >-
      Establishes that acute liver injury in hepatitis A is understood in terms
      of the adaptive immune response rather than viral replication alone, which
      is the basis for annotating this node with adaptive immunity and its
      effector cells. Evidence source is OTHER because this is a review.
  downstream:
  - target: Jaundice
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Hepatocellular injury with hyperbilirubinaemia
    description: >-
      Acute inflammatory liver injury impairs bilirubin handling enough to
      produce icterus in symptomatic infections.
  - target: Constitutional Prodrome
    causal_link_type: DIRECT
    description: >-
      The acute HAV inflammatory response produces the fever and malaise that
      precede jaundice in clinically apparent disease.
  - target: Dark Urine
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Conjugated hyperbilirubinaemia with bilirubinuria
    description: >-
      Cholestatic bilirubin accumulation during the acute inflammatory illness
      is excreted in urine, producing dark urine before or alongside jaundice.
  - target: Host-Factor-Dependent Severity Modulation
    causal_link_type: DIRECT
    description: >-
      Host immunological status, age, pregnancy, and pre-existing liver disease
      determine how severe the inflammatory reaction becomes.
  - target: Spontaneous Resolution and Lifelong Immunity
    causal_link_type: DIRECT
    description: >-
      In most people the inflammatory reaction resolves and leaves protective
      anti-HAV IgG.

- name: Host-Factor-Dependent Severity Modulation
  description: >-
    The severity of hepatitis A is set by the host, not by viral genotype.
    Immunological status, age, pregnancy, and underlying liver disease all
    modify the outcome, which is why universal childhood vaccination in
    intermediate-endemicity settings and targeted vaccination of people with
    chronic liver disease are both rational strategies. Paradoxically,
    improvements in sanitation that delay the age of first exposure increase the
    burden of symptomatic disease.
  role: amplifier
  biological_scale: ORGANISM
  evidence:
  - reference: PMID:37770459
    reference_title: "Hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Host factors, such as immunological status, age, pregnancy and underlying
      hepatic diseases, can affect the severity of disease.
    explanation: >-
      Names the host variables that modulate this node, the basis for
      risk-targeted vaccination. Evidence source is OTHER because this is a
      review.
  downstream:
  - target: Prolonged, Relapsing, or Fulminant Course
    causal_link_type: DIRECT
    description: >-
      Unfavourable host factors shift the acute reaction toward a prolonged,
      relapsing, or fulminant course.

- name: Prolonged, Relapsing, or Fulminant Course
  description: >-
    A minority of patients depart from the usual self-limited course. Up to 20%
    have a prolonged or relapsing illness, and fewer than 1% develop acute liver
    failure. Acute liver failure is the mechanism of death in hepatitis A;
    because no antiviral exists, management is supportive and, in the most
    severe cases, transplantation.
  role: consequence
  biological_scale: ORGANISM
  evidence:
  - reference: PMID:37770459
    reference_title: "Hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      However, up to 20% of patients experience a prolonged or relapsed course
      and <1% experience acute liver failure.
    explanation: >-
      Quantifies both departures from the usual course. Evidence source is OTHER
      because this is a review.
  downstream:
  - target: Acute Liver Failure
    causal_link_type: DIRECT
    description: >-
      Fulminant severe HAV courses cross the threshold into acute liver failure,
      the life-threatening complication documented in fewer than 1% of cases.

- name: Spontaneous Resolution and Lifelong Immunity
  description: >-
    In the great majority of cases the infection resolves without treatment and
    without chronic sequelae. Anti-HAV IgG produced in response to infection
    persists for life and protects against re-infection; vaccine-induced
    antibody confers long-term protection by the same mechanism. This node is
    the reason hepatitis A has no chronic arm at all - there is no persistent
    reservoir, no cirrhosis pathway, and no virus-driven hepatocellular
    carcinoma.
  role: consequence
  biological_scale: ORGANISM
  evidence:
  - reference: PMID:37770459
    reference_title: "Hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Anti-HAV IgG antibodies produced in response to HAV infection persist for
      life and protect against re-infection; vaccine-induced antibodies against
      hepatitis A confer long-term protection.
    explanation: >-
      Establishes lifelong humoral immunity after both natural infection and
      vaccination. Evidence source is OTHER because this is a review.
  - reference: PMID:34652109
    reference_title: "Hepatitis A."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The disease is usually self-limited, supportive care is often sufficient
      for treatment, and chronic infection or chronic liver disease does not
      occur.
    explanation: >-
      States explicitly that chronic infection does not occur, the guardrail
      that keeps this entry from being curated with a chronic arm. Evidence
      source is OTHER because this is a clinical review.
phenotypes:
- category: Clinical
  name: Jaundice
  description: >-
    Icterus with hyperbilirubinaemia, typical of symptomatic adult infection and
    usually absent in infected children.
  phenotype_term:
    preferred_term: Jaundice
    term:
      id: HP:0000952
      label: Jaundice
  evidence:
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Infection is often asymptomatic in children, but adults present with
      jaundice, abdominal pain, hepatitis, and hyperbilirubinemia.
    explanation: >-
      Documents jaundice as a presenting feature in adults. Evidence source is
      OTHER because this is a clinical review.
- category: Clinical
  name: Constitutional Prodrome
  description: >-
    Fever and malaise typically precede jaundice and are more common in older
    children and adults than in young children. Dark urine accompanies the
    prodrome but is curated separately below, since it is bilirubinuria - an
    early marker of the cholestatic component - rather than a constitutional
    symptom.
  phenotype_term:
    preferred_term: Fever
    term:
      id: HP:0001945
      label: Fever
  evidence:
  - reference: PMID:34652109
    reference_title: "Hepatitis A."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Classic symptoms include fever, malaise, dark urine, and jaundice and are
      more common in older children and adults.
    explanation: >-
      Lists the prodromal symptoms and their age distribution. Evidence source
      is OTHER because this is a clinical review.
- category: Clinical
  name: Dark Urine
  description: >-
    Darkened urine from bilirubinuria, typically appearing with or shortly
    before jaundice. It reflects renal excretion of conjugated bilirubin that
    the inflamed liver cannot clear into bile, so it is a marker of the
    cholestatic component of the illness rather than a constitutional symptom.
  phenotype_term:
    preferred_term: Dark urine
    term:
      id: HP:0040319
      label: Dark urine
  evidence:
  - reference: PMID:34652109
    reference_title: "Hepatitis A."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Classic symptoms include fever, malaise, dark urine, and jaundice and are
      more common in older children and adults.
    explanation: >-
      Documents dark urine among the classic presenting features. Evidence
      source is OTHER because this is a clinical review.
- category: Clinical
  name: Acute Liver Failure
  description: >-
    Fulminant hepatic failure occurs in fewer than 1% of patients and is the
    mechanism of hepatitis A mortality.
  frequency: VERY_RARE
  phenotype_term:
    preferred_term: Acute hepatic failure
    term:
      id: HP:0006554
      label: Acute hepatic failure
  evidence:
  - reference: PMID:37770459
    reference_title: "Hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      However, up to 20% of patients experience a prolonged or relapsed course
      and <1% experience acute liver failure.
    explanation: >-
      Provides the frequency of acute liver failure recorded here as VERY_RARE
      (<1%). Evidence source is OTHER because this is a review.
progression:
- phase: Incubation
  incubation_days: 15-50
  notes: >-
    Mean incubation about 28-30 days (range 15-50 days). Virions are shed in
    stool and detectable in blood before symptoms begin, so infectivity peaks
    before jaundice appears.
  evidence:
  - reference: PMID:28534888
    reference_title: "Hepatitis A Outbreaks in European Homosexual Men."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The mean incubation period is 28 days (range: 15-50)."
    explanation: States the mean and the range of the incubation period.
  - reference: PMID:1335649
    reference_title: "Clinical manifestations and diagnosis of hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The mean incubation period is approximately 30 days."
    explanation: Independent review giving the mean incubation period.
- phase: Prodromal (pre-icteric) phase
  duration: A few days to a week before jaundice
  notes: >-
    Fever, malaise, nausea, vomiting and anorexia begin about a month after
    exposure, and aminotransferases rise during this period. The prodrome is
    common in adults and uncommon in children, whose infections are usually
    asymptomatic.
  evidence:
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Prodromal symptoms occur about a month following exposure and can consist of fever, malaise, nausea, vomiting, and anorexia."
    explanation: Times the prodrome and lists its symptoms.
  - reference: PMID:1335649
    reference_title: "Clinical manifestations and diagnosis of hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The onset of hepatitis A is often abrupt and characteristic prodromal symptoms are followed, within a few days to a week, by dark urine and jaundice."
    explanation: Gives the duration of the prodrome before jaundice appears.
- phase: Icteric phase
  duration: Jaundice usually under 2 weeks; biochemical peak 7-10 days after its onset
  notes: >-
    Dark urine and jaundice follow the prodrome, with hyperbilirubinaemia
    peaking 7 to 10 days after jaundice appears; jaundice persists for under
    two weeks in about 85% of cases.
  evidence:
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Adult infections will typically also be characterized by jaundice, diarrhea, and hyperbilirubinemia, peaking 7 to 10 days after the onset of jaundice."
    explanation: Times the biochemical peak of the icteric phase.
  - reference: PMID:1335649
    reference_title: "Clinical manifestations and diagnosis of hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Nonetheless, the period of jaundice persists for < 2 weeks in approximately 85% of cases."
    explanation: Gives the usual duration of jaundice.
- phase: Convalescence
  duration: Up to about 6 months to full biochemical recovery
  notes: >-
    Jaundice resolves faster than malaise and anorexia, which can last for
    months; nearly all adults recover completely, with normal bilirubin and
    aminotransferases by 6 months. HAV never establishes chronic infection or
    chronic liver disease, so there is no chronic phase to list.
  evidence:
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Jaundice will typically resolve much faster than the malaise and anorexia, which can last for months."
    explanation: Describes the convalescent course of the constitutional symptoms.
  - reference: PMID:1335649
    reference_title: "Clinical manifestations and diagnosis of hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Nearly all adult patients with clinically apparent disease experience complete clinical recovery with restoration of normal serum bilirubin and aminotransferase values by 6 months."
    explanation: Gives the time to complete clinical and biochemical recovery.
  - reference: PMID:34652109
    reference_title: "Hepatitis A."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The disease is usually self-limited, supportive care is often sufficient for treatment, and chronic infection or chronic liver disease does not occur."
    explanation: Supports the absence of any chronic phase.
- phase: Relapsing or prolonged cholestatic course (variant)
  duration: Relapse within 6 months of the index illness; cholestasis up to 1 year
  notes: >-
    A recognised variant course rather than a stage every patient passes
    through. A prolonged or relapsing illness is reported in up to 20% of
    patients in one review and described as infrequent in others; relapse
    brings recurrent symptoms, renewed faecal HAV shedding and raised
    transaminases, typically within 6 months, and prolonged cholestasis has
    been reported for up to a year. Recovery remains the rule even in these
    cases, and chronic hepatitis does not follow.
  evidence:
  - reference: PMID:37770459
    reference_title: "Hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "However, up to 20% of patients experience a prolonged or relapsed course and <1% experience acute liver failure."
    explanation: Quantifies the prolonged or relapsing course.
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "A relapsing hepatitis is infrequently seen in adult infections with recurrent symptoms typically occurring within 6 months of prior infection."
    explanation: Times the relapsing course.
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Hepatitis A–associated prolonged cholestasis has also been reported after infection, for periods up to 1 year."
    explanation: Gives the duration of the prolonged cholestatic variant.
  - reference: PMID:1335649
    reference_title: "Clinical manifestations and diagnosis of hepatitis A virus infection."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Relapses and prolonged cholestasis are unusual manifestations of hepatitis A, and even in these circumstances, recovery is the rule and chronic hepatitis is not seen."
    explanation: Confirms recovery and the absence of chronic hepatitis after the variant courses.
diagnosis:
- name: Anti-HAV IgM Serology
  description: >-
    Acute hepatitis A is diagnosed by detecting IgM antibodies against HAV.
    Anti-HAV IgG, in contrast, marks past infection or vaccination and confers
    protection rather than indicating current disease.
  evidence:
  - reference: PMID:34652109
    reference_title: "Hepatitis A."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Diagnosis of acute infection requires the use of serologic testing for
      immunoglobulin M anti-hepatitis A antibodies.
    explanation: >-
      States the diagnostic test for acute infection. Evidence source is OTHER
      because this is a clinical review.
treatments:
- name: Supportive Care
  description: >-
    There is no specific antiviral therapy for hepatitis A. Because the disease
    is self-limited in almost all patients, supportive care is sufficient;
    management is escalated only for the small minority developing acute liver
    failure.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:34652109
    reference_title: "Hepatitis A."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The disease is usually self-limited, supportive care is often sufficient
      for treatment, and chronic infection or chronic liver disease does not
      occur.
    explanation: >-
      Establishes supportive care as sufficient treatment for the usual course.
      Evidence source is OTHER because this is a clinical review.
- name: Hepatitis A Vaccination
  description: >-
    Inactivated hepatitis A vaccine is the mainstay of prevention and works by
    inducing the same lifelong protective antibody that natural infection
    produces. It is used both for routine childhood immunisation and for
    pre-exposure and post-exposure prophylaxis; immune globulin substitutes when
    the vaccine is contraindicated or the recipient is too young. Programme-level
    deployment has measurably reduced HAV incidence.
  therapeutic_modality: VACCINE
  treatment_term:
    preferred_term: Vaccination
    term:
      id: NCIT:C15346
      label: Vaccination
  target_mechanisms:
  - target: Faecal-Oral Acquisition and Hepatocyte Infection
    treatment_effect: INHIBITS
    description: >-
      Vaccine-induced anti-HAV antibody neutralises the virus before hepatocyte
      infection is established, preventing the whole downstream chain rather
      than modifying it.
    evidence:
    - reference: PMID:37770459
      reference_title: "Hepatitis A virus infection."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        To date, >25 countries worldwide have implemented such programmes,
        resulting in a reduction in the incidence of HAV infection.
      explanation: >-
        Provides population-level evidence that vaccination prevents infection
        rather than merely attenuating disease. Evidence source is OTHER because
        this is a review summarising national programme outcomes.
  evidence:
  - reference: PMID:32389358
    reference_title: "Hepatitis A: Epidemiology, Natural History, Unusual Clinical Manifestations, and Prevention."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Vaccination is the mainstay of prevention and should be given before
      exposure whenever possible.
    explanation: >-
      States the role of vaccination in prevention. Evidence source is OTHER
      because this is a clinical review.
  - reference: PMID:34652109
    reference_title: "Hepatitis A."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The vaccine is usually recommended for pre- and postexposure prophylaxis,
      but immune globulin can be used in patients who are too young to be
      vaccinated or if the vaccine is contraindicated.
    explanation: >-
      Documents the pre- and post-exposure indications and the immune globulin
      alternative. Evidence source is OTHER because this is a clinical review.

discussions:
- discussion_id: hav_immunopathogenesis_unsettled
  kind: KNOWLEDGE_GAP
  prompt: >-
    How does adaptive immunity produce the liver injury of hepatitis A, as
    distinct from clearing the virus - and why does HAV never persist?
  attaches_to:
  - "pathophysiology#Acute Hepatic Inflammatory Reaction"
  - "pathophysiology#Host-Factor-Dependent Severity Modulation"
  rationale: >-
    This entry asserts that severity is host-determined, and annotates the
    inflammatory node with adaptive immunity accordingly, but the mechanism
    connecting the two is not settled. The review literature states plainly that
    how HAV is so effectively controlled by B and T cell immunity, and why it
    lacks the propensity to persist that HBV and HCV have, cannot yet be
    adequately explained, and that recent work challenges long-held concepts of
    how antibodies and T cells contribute to pathogenesis. The entry therefore
    deliberately stops short of curating a specific cytotoxic effector
    mechanism: naming CD8 or NK-mediated killing as the cause of hepatocyte
    injury would assert more than the cited evidence supports.
  proposed_experiments:
  - experiment_id: hav_intrahepatic_immune_profiling
    name: Intrahepatic immune profiling across the age-severity gradient
    description: >-
      Comparing intrahepatic T cell, NK cell and antibody responses between
      asymptomatic infected children and symptomatic infected adults in the same
      outbreak would test directly whether the age-dependent severity this entry
      models is produced by the adaptive response, and identify which effector
      arm causes the injury.

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