Hepatitis E was not recognized as a distinct human disease until 1980. Hepatitis E is caused by infection with the hepatitis E virus, a single-stranded RNA virus.

Although humans are considered the natural host for human hepatitis E virus (HEV), antibodies to HEV or closely related viruses have been detected in primates and several other animal species suggesting that hepatitis E may be a zoonosis (i.e. a disease that animals can transmit to humans).

How is HEV transmitted?

Hepatitis E is a waterborne disease, and contaminated water or food supplies have been implicated in major outbreaks. Consumption of faecally contaminated drinking water has given rise to epidemics, and the ingestion of raw or uncooked shellfish has been the source of sporadic cases in endemic areas. There is a possibility of spread of the virus from animals, since several non-human primates, pigs, cows, sheep, goats and rodents are susceptible to infection. The risk factors for HEV infection are related to poor sanitation in large areas of the world.

Person-to-person transmission is thought to be uncommon. There is no evidence for sexual transmission or for transmission by transfusion.

Where is HEV a problem?

Epidemics of hepatitis E have been reported in Central and South-East Asia, North and West Africa, and in Mexico, especially where faecal contamination of drinking water is common. However, sporadic cases of hepatitis E have also been reported elsewhere and serological surveys suggest a global distribution of strains of hepatitis E which cause asymptomatic or mild disease (low pathogenicity).

When is a HEV infection life-threatening?

In general, hepatitis E is a self-limiting viral infection followed by recovery. Prolonged shedding of the virus in faeces is unusual and chronic infection does not occur.

Overall, patient population mortality rates range from 0.5% - 4.0%. Occasionally, a sudden and severe form of hepatitis develops in which cells of the liver die, the liver shrinks and death can follow. This form of the disease, known as fulminant hepatitis, occurs more frequently in pregnancy and is associated with a mortality rate of 20% among pregnant women in the 3rd trimester.

The disease

The incubation period following exposure to HEV ranges from 3 to 8 weeks. The period during which an infected person can transmit the disease is unknown.

Typical signs and symptoms of hepatitis include jaundice (yellow discoloration of the skin and sclera of the eyes, dark urine and pale stools), anorexia (loss of appetite), an enlarged, tender liver (hepatomegaly), abdominal pain and tenderness, nausea and vomiting, and fever, although the disease may range in severity from mild to life-threatening.

Symptomatic HEV infection is most common in young adults aged 15-40 years. Although HEV infection is frequent in children, it is mostly asymptomatic or causes a very mild illness without jaundice that goes undiagnosed.

Diagnosis

Since cases of hepatitis E are not clinically distinguishable from other types of acute viral hepatitis, diagnosis is made by blood tests which detect elevated antibody levels of specific antibodies to hepatitis E in the body or by detecting small portions of genetic material through a test known as reverse transcriptase polymerase chain reaction (RT-PCR). Unfortunately, such tests are not widely available.

Hepatitis E should be suspected in outbreaks of waterborne hepatitis occurring in developing countries, especially if the disease is more severe in pregnant women, or if hepatitis A has been excluded. If laboratory tests are not available, epidemiologic evidence can help in establishing a diagnosis.

Vaccines

At present, no commercially available vaccines exist for the prevention of hepatitis E. However, several studies for the development of an effective vaccine against hepatitis E are in progress.

Prevention

As almost all HEV infections are spread by the faecal-oral route, good personal hygiene, high quality standards for public water supplies and proper disposal of sanitary waste are the most important public health interventions in the prevention of hepatitis E.

For travelers to highly endemic areas, the usual food and water hygiene precautions are recommended. These include avoiding drinking water and/or ice of unknown purity and eating uncooked shellfish, uncooked fruits or vegetables that are not peeled or prepared by the traveler.

Treatment

Hepatitis E is a viral disease, and as such, antibiotics are of no value in the treatment of the infection. There is no hyperimmune hepatitis E globulin available for pre- or post-exposure prophylaxis. HEV infections are usually self-limited, and hospitalization is generally not required. No available therapy is capable of altering the course of acute infection, and therefore prevention is the most effective approach against the disease.

Hospitalization is required for fulminant hepatitis and should be considered for infected pregnant women.

Thanks to the World Health Organisation
for much of this information.