Genotype 3 hepatitis E has been widespread in pig farms of Shanghai suburbs

Hepatitis E virus (HEV) genotype 3 was first identified in swine raised on a Shanghai suburban pig farm in late 2006. To accurately determine the prevalence of HEV infections among Shanghai pig farms, 426 pig fecal samples were collected from 37 pig farms located in all 10 Shanghai suburban districts and tested for the presence of HEV RNA using RT-PCR. Genetic analysis based on an amplified 150-bp ORF2 fragment revealed 111 samples to be HEV positive, and the prevalence of HEV infection within the different districts varied between 0 and 41.7%. Thirty-two samples were sequenced, and phylogenetic analysis indicated that 10 isolates belonged to HEV genotype 4 and were most closely related to 3 human and 2 swine HEV strains, all of which had originally been isolated from Asian countries including Japan and China. The remaining 22 isolates belonged to genotype 3 and were most closely related to a strain of swine HEV, US-SW, isolated from pigs in the United States. Our data indicated that genotype 3 HEV was widespread among suburban Shanghai pig farms although further study is required to determine the source and zoonotic nature of the virus.