The goal of this project is to characterize hepatitis E virus (HEV), to determine the extent and pattern of its involvement in enterically transmitted hepatitis, and to develop a vaccine for the prevention of hepatitis E.Previously we identified and sequenced a hepatitis E virus that was ubiquitous in US swine and that was genetically divergent from other strains of HEV. We are examining sera from around the world and from other animal species in order to determine whether animal strains of HEV are widespread and, if so, what their genetic relationship is to each other and to human strains. We have shown that the majority of rats from 3 different geographical regions of the U.S. have antibody to HEV and thus rats may be a potential source of HEV infection in humans. We have shown that humans in Egypt have an unusually high prevalence of anti-HEV (~ 70%) even though epidemics of hepatitis E are uncommon there. We have purified a baculovirus-expressed recombinant capsid protein for additional vaccine studies in rhesus monkeys and have prepared material which was used for phase I and phase II clinical trials. A phase II/III clinical trial is scheduled to begin in Nepal. A combinatorial phage Fab display library has been prepared from bone marrow cells of a chimpanzee that had been infected with HEV. Our recombinant HEV capsid protein was used to screen this library for monoclonal antibodies to HEV. Seventeen monoclonal antibodies were isolated and two of four that were tested neutralized the virus. The corresponding epitopes are being mapped. Since chimpanzee and human monoclonal antibodies are virtually identical, it should be possible to use such neutralizing antibodies for passive immunoprophylaxis in humans. We have constructed a full-length cDNA clone of HEV and are testing it for infectivity in macaques.