Hepatitis E: a puzzling double-faced disease.

Viral hepatitis type E is highly endemic in many developing countries, where large water-borne epidemics caused by viral genotype 1 and - to a lesser degree - by genotype 2 cyclically occur, resulting in high morbidity and mortality, especially among pregnant women. In developed countries, the disease is usually diagnosed in travelers coming back from endemic countries, but an increasing number of sporadic locally acquired hepatitis cases caused by genotype 3 and 4 have recently been reported. The wide-spread distribution of HEV3 and HEV4 in domestic pigs, wild boars, deer, as well as in other mammals, suggests that infections caused by these genotypes may have a zoonotic source. HEV3 infection can evolve to chronic infection in immunosuppressed patients; in addition, it may be associated with neurological disorders and extrahepatic manifestations. Two recently developed recombinant vaccines have proved to be safe and effective. One of such vaccines has recently been licensed for use in China.