The Global Impact of Hepatitis E: New Horizons for an Emerging Virus

An appreciation of the role of the fifth human hepatitis virus, hepatitis E virus (HEV), as an important cause of acute, and occasionally chronic, hepatitis in humans has increased in recent years. Hepatitis viruses have long been implicated as the cause of substantial morbidity and mortality in the developing world, through both sporadic and epidemic disease. The predictable seasonal outbreaks, coincident with the monsoon rains, have provided numerous opportunities to study risk factors for HEV infection, the clinical course of hepatitis E disease, and the characteristics of the virus. In 1980, by excluding hepatitis A virus (HAV) and hepatitis B virus (HBV) as causes of a large 1955 to 1956 hepatitis epidemic in India, two groups independently reported the hypothesis of a novel, enterically transmitted non-A, non-B (ET-NANB) virus. As HEV shares certain morphologic and biophysical properties with members of the Caliciviridae family, it was initially classified as a calicivirus. Electron microscopy has been used to detect virus-like particles in the livers of patients with HEV-attributable fulminant hepatitis. The age- and gender-matched control group in a case control study in Sudan found a high (18%) anti-HEV IgG seroprevalence among children in the general population. Immunologic changes of pregnancy, such as the down-regulation of TH1 cytokines, and hormonal changes may also influence pathogenesis. A recent case report of fulminant hepatitis due to infection with an HEV genotype 3 strain in a patient in Spain has suggested that an important cofactor was the usage of hormonal contraceptives.