Hepatitis E Virus and Zoonosis

Abstract

Hepatitis E virus (HEV) is an important public health problem both in developing and developed nations. HEV is a single stranded RNA non-enveloped virus belonging to the family Hepeviridae. Globally, HEV is known to cause approximately 20 million infections per annum with a mortality of 44,000. The virus is endemic in developing nations and the outbreaks occur mainly in the post monsoon season when the drinking water gets contaminated with sewage. However, the mode of acquisition of infection is different in developed nations with good sanitary conditions where the infection is a zoonosis. Though the virus has only one serotype, 8 genotypes have been documented. Out of these, HEV 1 and 2 have been reported from developing countries and are transmitted mainly through faeco-oral route while HEV 3 and 4 are reported from developed countries and the infection is acquired by humans due to the eating of undercooked pigs, deer and wild boar meat. Recently HEV genotypes 5 and 6 have been reported in Japanese wild boars while HEV genotypes 7 and 8 have been reported in camels from Middle-East countries. Considering the increasing globalization of food markets, the possibility exists of widespread HEV infection in new areas of the world. In the present era, there is a need to study transmission dynamics of HEV in context to humans, animals and the environment so as to develop better prevention control measures through 'One Health' concept. The clinical manifestations of HEV can vary from self-limiting acute viral hepatitis which occurs in apparently healthy individuals to acute liver failure which leads to high mortality among pregnant women. Recently, chronic infections due HEV genotypes 3 and 4 have also been documented in immunosuppressed and transplant patients where prolonged virus shedding has been documented. The conventional diagnosis is established by detection of HEV antigen or anti-HEV IgM in acute sera. However, the detection of HEV RNA is important to establish the diagnosis in immunosuppressed patients. In transplant patients, decrease in immunosuppression is usually done, however ribavirin therapy has also shown a definitive role. There is upcoming literature on the role of sofosbuvir also in these groups of patients. Since the virus has only one serotype, univalent vaccine can provide protection against all HEV genotypes. Two vaccine candidates have been evaluated in clinical trials. Among these two vaccine candidates, one has been developed by Glaxosmithkline and another HEV 239 (Hecolin) has been developed by Innovax (China) and is in use in China since 2012. Considering the expanding clinical spectrum of HEV, it is an emerging zoonotic illness and prevention is the most effective approach against HEV.