Hepatitis e: epidemiology and natural history

Abstract

Hepatitis E is a disease caused by infection with hepatitis E virus (HEV). The virus has four genotypes, named 1 to 4, with one shared serotype. Genotypes 1 and 2 infect only humans, whereas genotypes 3 and 4 primarily infect several mammalian animals, with occasional transmission to humans. Evidence of infection with HEV has been found in most parts of the world, with two distinct epidemiological patterns. In areas with high disease endemicity, primarily developing countries in Asia and Africa, the disease occurs as outbreaks and as sporadic cases of acute hepatitis, and is caused exclusively by infection with genotypes 1 or 2 HEV, which is acquired through fecal-oral route, usually through contamination of water supplies. The disease in these areas occurs most commonly in young adults, and is particularly severe in pregnant women and persons with pre-existing chronic liver disease; chronic infection has not been reported. In areas with lower endemicity, which are mainly developed areas with robust water supply and sanitation systems, occasional sporadic cases of locally-acquired genotype 3 or 4 HEV infection are observed. The affected persons are often elderly and have other coexisting illnesses. The reservoir of infection in these areas is believed to be in animals, such as pigs, wild boar and deer, with zoonotic transmission to humans, possibly through consumption of undercooked meat. Also, in these areas, persistent HEV infection has been well documented among immunosuppressed persons such as organ transplant recipients, and is believed to lead to chronic liver injury, including liver cirrhosis. Further work is needed to better understand the biological basis underlying these widely-differing epidemiological patterns.

Keywords: FHF, fulminant hepatic failure; HEV, hepatitis E virus; NHANES, National Health and Nutrition Examination survey; NTP, nucleoside triphosphate; ORF, open reading frames; endemic; epidemiology; hepatitis E; hepatitis E virus; natural history.

Figure 1

Distribution of HEV genotypes in viral isolates obtained from humans and animals (mainly pigs). The colors used for a country and the circle associated with it represent the predominant HEV genotypes of human and animal isolates, respectively, from that country. The figure is based on data from Okamoto, 2007.

Figure 2

Map showing areas with high-endemicity for hepatitis E.