A strain of hepatitis E virus (SAR-55) implicated in an epidemic of enterically transmitted non-A, non-B hepatitis, now called hepatitis E, was characterized extensively. Six cynomolgus monkeys (Macaca fascicularis) were infected with a strain of hepatitis E virus from Pakistan. Reverse transcription-polymerase chain reaction was used to determine the pattern of virus shedding in feces, bile, and serum relative to hepatitis and induction of specific antibodies. Virtually the entire genome of SAR-55 (7195 nucleotides) was sequenced.Comparison of the sequence of SAR-55 with that of a Burmese strain revealed a high level of homology except for one region encoding 100 amino acids of a putative nonstructural polyprotein. Identification of this region as hypervariable was obtained by partial sequencing of a third isolate of hepatitis E virus from Kirgizia.

The age-specific seroprevalence of antibody to hepatitis A virus (HAV) and antibody to hepatitis E virus (HEV) were studied in persons in Pune, India, where both viruses are endemic. The data showed that HAV infected the majority of persons by age 3 years and virtually 100% by late childhood. In contrast, infection with HEV was rare in children and did not reach peak prevalence (33%-40%) until early adulthood. The reason for the differences in infection rates between HAV and HEV is not known. Age-specific antibody patterns in serum samples obtained 10 years apart show that neither HAV nor HEV has diminished in medical importance in this Indian community.

A recombinant baculovirus containing the complete open-reading frame (ORF)-2 region of the hepatitis E virus (HEV) genome was constructed. The major protein synthesized in insect cells infected with recombinant virus was about the size expected for the complete ORF-2 product. This protein reacted in a Western blot assay with plasma from an HEV-infected chimpanzee. Lysates of the recombinant virus-infected insect cells were used in ELISA to monitor seroconversion of eight primate species (chimpanzees, four species of Old World monkeys, and three species of New World monkeys) inoculated with HEV. Homologous detector anti-immunoglobulin was more sensitive than heterologous anti-immunoglobulin for detecting anti-HEV by ELISA. All primate species except tamarins seroconverted after inoculation with HEV, although anti-HEV titers of Old World monkey species were generally higher than those of New World monkey species. The ELISA with complete ORF-2 antigen appeared to be a sensitive and practical method for detecting anti-HEV.

Many epidemics of water-borne hepatitis have occurred throughout India. These were thought to be epidemics of hepatitis A until 1980, when evidence for an enterically transmitted non-A, non-B hepatitis was first reported. Subsequently, hepatitis E virus was discovered and most recent dem of enterically ted non-A, non-B hepatitis have been attributed to hepatitis E virus infection. However, only a limited number of cases have been confirmed by immuno electron microscopy, polymerase chain reaction, or seroconversion. In the present study we have performed a retrospective seroepidemiologic study of 17 epidemics of waterborne hepatitis in India. We have confirmed that 16 of the 17 epidemics were caused at least in part by serologically closely related hepatitis E viruses. However, one epidemic, in the Andaman Islands, and possibly a signifnt minrit of cases in other epidemics, appears to have been caused by a previously unrecognized hepatitis agent.