exulans rats trapped in several US cities (Baltimore, Maryland New Orleans, Louisiana and the islands of Oahu and Hawaii, Hawaii) were positive for antibodies against HEV ( 12). We have demonstrated that a high proportion of wild-caught Rattus norvegicus, R. Rats are particularly interesting as a potential source of human infections because although they are not a human food, they have a high seroprevalence of antibodies against HEV ( 12, 13) and they are ubiquitous and in close contact with humans everywhere.
Thus, it is important to understand how this rat virus is related to human infections. However, an HEV strain recently isolated from rats was unique and only distantly related to known strains ( 11). Numerous species, including rodents, have been found to have antibodies reactive with capsid protein of human HEV strains, and HEV closely related to genotypes 3 or 4 has been recently isolated from rabbits ( 8), cattle ( 9), and sheep ( 10). Therefore, eating pork is unlikely to explain the prevalence of antibodies against HEV in this country. It is noteworthy that swine handlers in the United States have a higher incidence of antibodies against HEV than do healthy blood donors, even though pork is generally thoroughly cooked in the United States. However, many, if not most, persons who have unexplained antibodies against HEV do not eat undercooked pork or venison, raising the possibility that other animals or modes of zoonotic transmission exist. Strains of HEV representing genotypes 3 and 4, which have been isolated from humans with hepatitis E, regularly infect pigs worldwide ( 6), and infection in humans caused by eating undercooked meat from domestic pigs, wild boar, and several species of wild deer has been documented ( 6, 7). Additionally, a large proportion ( <20%) of populations of such countries have antibodies against HEV in the absence of any recognized hepatitis ( 3 – 5), and evidence is increasing that these antibodies might be the result of subclinical infections acquired zoonotically. Recently, hepatitis E has been diagnosed with increasing frequency as a cause of sporadic hepatitis in industrialized countries ( 2). Hepatitis E is caused principally by HEV genotypes 1 and 2 ( 1). Hepatitis E virus (HEV) is a major cause of epidemic waterborne and sporadic hepatitis in developing countries.
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