The two faces of hepatitis E virus.

Hepatitis E virus (HEV) has at least 2 distinct epidemiological profiles: (1) large outbreaks and epidemics in developing countries, usually caused by HEV genotype 1, resulting in high morbidity and mortality among pregnant women and young children, and (2) very few symptomatic cases of HEV genotype 3, most cases without symptoms or clear source(s) of infection, but frequent seroreactivity in 5%-21% of asymptomatic persons in developed countries. We urge more epidemiological studies and public health interventions, including the promotion and development of existing and future vaccine candidates and the availability of US Food and Drug Administration-approved serological assays for this underappreciated and poorly understood virus, a major cause of disease throughout the world.