HAV is a member of the Picornaviridae family. HAV is a non-enveloped (naked) virus of 27–28 nm diameter without morphological features differentiating it from other picornaviruses. Although six genotypes of HAV have been identified, there appears to be no variation detectable by serology in these neutralization sites. The virus is relatively stable at low pH and moderate temperatures, but is inactivated by high temperature (almost instantly at 85°C/185°F), and by formalin or chlorine.

HAV itself is not cytopathic and the liver-cell damage is caused by the cell-mediated immune response.

The clinical course of acute hepatitis A is indistinguishable from other types of acute viral hepatitis. Symptoms typically include

• fever
• malaise
• anorexia,
  
• nausea and abdominal discomfort,
• followed by dark urine and jaundice.
  

The severity of disease and mortality increases in older age groups. The convalescence following hepatitis A may be slow, and is characterized by

• fatigue,
  
• nausea and
  
• lack of appetite.
  

Complications of hepatitis A include

• relapsing hepatitis,
  
• cholestatic hepatitis and
  
• fulminant hepatitis.
  

Fulminant hepatitis occurs in approximately 0.01% of clinical infections and is characterized by rapid deterioration in liver function and a very high fatality rate.

Chronic infection with HAV does not occur.

No specific antiviral therapy is currently available.

 A second option for protecting people against hepatitis A is to administer antibodies that are already programmed to attack the virus. When people donate blood, the part of the blood carrying antibodies (the immune globulin fraction) can be separated. Because some blood donors are likely to have antibodies against the hepatitis A virus, pooled immune globulin from many donors is likely to contain antibodies against hepatitis A. This immune globulin can be injected into a person at risk for hepatitis A and will provide immediate but temporary protection against infection. Protection with immune globulin lasts two to four months depending on the dose. Immune globulin is used when immediate protection against hepatitis A is required. An example would be someone who is leaving immediately to travel to rural areas of a developing country. Such a traveler would also receive hepatitis A vaccine but would not have time to develop antibodies before departure.

These measures will reduce the risk that the exposed person will contract hepatitis A by 85% to 90% if given within two weeks of exposure.

Immune globulin currently is recommended for exposed persons over the age of 40 years. 

• travelers to developing countries,
  
• men who have sex with men,
  
• users of illicit drugs,
  
• persons needing frequent blood products, and
  
• people who have chronic liver disease.

Protective antibodies develop in response to infection and persist for life.

The protective role of anti-HAV antibodies has been demonstrated by the protection against hepatitis A resulting from passive immunization with serum immune globulin.