Journal of Virology, December 1998, p. 9714-9721, Vol. 72, No. 12
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 208921; Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, Iowa 500112; Bioqual, Inc., Rockville, Maryland 208503; Pathology and Clinical Laboratories, Rancho Los Amigos Medical Center, Downey, California 902424; and Viral Discovery Group, Abbott Laboratories, North Chicago, Illinois 600645
Received 26 May 1998/Accepted 24 August 1998
Prior to the recent discovery of the swine hepatitis E virus (swine
HEV) in pigs from the midwestern United States, HEV was not considered
endemic to this country. Since swine HEV is antigenically and
genetically related to human strains of HEV, it was important to
characterize this new virus further. The infectivity titer of a pool of
swine HEV in pigs was determined in order to prepare a standardized
reagent and to evaluate the dose response in pigs. Although the
sequence of swine HEV varied extensively from those of most human
strains of HEV, it was very closely related to the two strains of human
HEV (US-1 and US-2) isolated in the United States. The U.S. strains
which were recently recovered from two patients with clinical hepatitis
E in the United States shared
97% amino acid identity with swine HEV
in open reading frames 1 and 2. Phylogenetic analyses of different
regions of the genome revealed that swine HEV and the U.S. strains
grouped together and formed a distinct branch. These results suggested
that swine HEV may infect humans. When we inoculated rhesus monkeys and
a chimpanzee, experimental surrogates of humans, with swine HEV, the
primates became infected. Furthermore, in a reciprocal experiment, specific-pathogen-free pigs were experimentally infected with the US-2
strain of human HEV that is genetically similar to swine HEV. These
results provided experimental evidence for cross-species infection by
the swine virus. Thus, humans appear to be at risk of infection with
swine HEV or closely related viruses.
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