Hepatitis A virus infection is acquired primarily by the faecal-oral route, by person-to-person contact or by the ingestion of faecally contaminated food or water. The virus has a worldwide distribution and causes about 1.4 million cases of clinical hepatitis each year. Humans are the only reservoir of the virus.
The incubation period of hepatitis A is approximately 28 days (range 15-50 days) and illness typically has an abrupt onset of fever, malaise, anorexia, nausea, abdominal discomfort, dark urine and jaundice. After 10-12 days of infection, virus is present in blood and is excreted into the faeces (persists up to 2-3 weeks).
Children may excrete virus longer than adults and play an important role in Hepatitis A transmission. As children generally are asymptomatic or have unrecognized illnesses, they may serve as an unknown source of infection for household or other close contacts. Groups at increased risk for hepatitis A or its complications include international travelers, men who have sex with men (MSM), and intravenous drug users.
The incidence of hepatitis A is closely related to socioeconomic development (e.g sanitation and hygienic conditions). Sero-epidemiological studies show that prevalence of anti-Hepatitis A antibodies in the general population varies from 15% to close to 100% in different parts of the world.
In countries highly endemic for hepatitis A, almost all persons are infected during childhood. Ninety percent of infections in children are subclinical or asymptomatic which effectively prevents clinical hepatitis A in adolescents and adults. In countries of low and intermediate disease endemicity, disease and consequently more severe infections are seen more often. These are moslty adults, since the severity of the disease increases with age. Infection with Hepatitis A virus induces lifelong immunity.
Besides a good personal hygiene, high quality standards for public water supplies and proper disposal of sanitation, vaccination against Hepatitis A is a good preventive measure. At least four inactivated vaccines are presently commercially available in some parts of the world. Inactivated Hepatitis A vaccines are safe, highly immunogenic, and provide long-term protection from Hepatitis A infection (WHO). Hepatitis A vaccination is recommended for persons at increased risk of acquiring hepatitis A, such as MSM, or travelers to endemic countries.
Passive immunization of IgG can also be used in non-vaccinated people, mostly for post exposure prophylaxis. If IgG antibodies or inactivated vaccines are administered within two weeks of exposure it can either prevent development or reduce the severity of the disease. Universal immunization against hepatitis A would successfully control the disease, however it still depends on the costs and different country policies.
The Hepatitis A virus is a non-enveloped RNA virus, member of the genus Hepatovirus of the Picornaviridae family. There are 6 Hepatitis A genotypes (I to VI) in which genotypes I, II and III comprise human isolates and genotypes IV, V, and VI comprise only simian isolates. Genotypes I to III is subdivided in two distinct groups A and B.