The virus

Hepatitis E virus (HEV) is an RNA virus that resembles caliciviruses but as yet remains unclassified. There are at least four genotypes of the virus, genotypes 1 and 2 are limited to humans only, and genotype 3 and 4 have animals as their reservoir and therefore are zoonotic infections.

Epidemiology

Route of spread

Hepatitis E is spread by the faecal–oral route, mostly through drinking water and probably by eating contaminated food. Person-to-person spread may occur but is uncommon. Waterborne outbreaks occur commonly in countries where infection is endemic.

Prevalence

The infection was first reported from the Indian subcontinent and subsequently from other parts of Asia, the Middle East, Central and South America, Africa, Central Europe and Russia. People travelling to countries with high prevalence are therefore at risk of acquiring infection during their travel. Adult populations in endemic areas are generally susceptible and there is a high infection rate in epidemics.

Until recently cases reported from North America and Western Europe were travel related but recently many indigenous cases, including clusters of cases, have been reported indicating that hepatitis E infection is endemic. All the cases reported from the West have been due to genotype 3 of HEV, for which pigs are the main reservoir. The exact route of transmission is not clear and further studies are needed.