Epidemics of enterically transmitted non-A, non-B hepatitis (hepatitis E) have been reported in Asia, Africa, and North America but not in the United States or Canada. Similar cases of sporadic hepatitis, presumed to be hepatitis E, account for up to 90% of reported acute hepatitis in countries where hepatitis E is endemic. Hepatitis E virus (HEV) has been implicated in fulminant hepatitis of pregnancy. This disease has a 20% fatality rate. The goal of this project is to characterize 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. Following our discovery of a high prevalence of antibody to hepatitis E virus (anti-HEV) in commercially raised swine in the United States, we prospectively monitored baby pigs in a production facility. Seventeen of twenty piglets developed anti-HEV. HEV sequences were amplified by RT-PCR from the serum and feces taken just before seroconversion from several piglets. We transmitted an agent to specific pathogen free pigs, recovered the agent and sequenced its entire genome. The transmissible agent was a hepatitis E virus that was genetically divergent from other strains of HEV. Subsequently, two human cases of hepatitis E in the US yielded viruses very closely related to the swine HEV. At least one of the US non-human isolates (supplied by I. Mushahwar) and the US swine isolate were transmissible both to non-human primates and swine. Thus, we have discovered a new and ubiquitous swine HEV that appears to be capable of infecting humans under some circumstances. 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 also are continuing our work on a vaccine for hepatitis E. We have purified a baculovirus-expressed recombinant capsid protein for additional vaccine studies in rhesus monkeys and have prepared material for phase I clinical trials which should begin shortly. 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. Two monoclonal antibodies were isolated and are currently being tested for their ability to neutralize the virus. Since chimpanzee and human monoclonal antibodies are virtually identical, it should be possible to use such antibodies for passive immunoprophylaxis of humans if these immunoglobulins prove to exhibit a high level of neutralizing activity. An infectious cDNA clone of HEV would greatly improve our ability to study the molecular biology of this virus. To this end, we are heeding lessons learned from our studies of hepatitis C virus, and are constructing a cDNA clone that contains the consensus sequence of our prototype HEV strain. The cDNA clone is almost completed and soon transcripts from it will be inoculated into rhesus monkeys to test for infectivity in vivo.
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