Investigation of hepatitis E virus infection in swine from Hunan province, China.

Nine hundred and four serum samples were collected from pigs from 16 pig farms in China's Hunan province and tested for anti-hepatitis E virus (HEV) antibody and the HEV capsid antigen using EIAs. Of the 904 samples, 617 (68.3%) and 57 (6.3%) were positive for anti-HEV antibody and antigen, respectively. The prevalence of HEV antibodies and detection of antigen varied significantly among pigs from different farms (P < 0.01). The positivity rate for anti-HEV antibody and occurrence of high titer antibody were significantly higher in pigs above, than in those below, 3 months of age, whilst the detection of antigen did not differ significantly between the two groups. Based on these data, 481 serum samples that were positive for HEV antigen or with an S/CO < or =10 for anti-HEV were tested for HEV RNA using real-time RT-PCR; 28 of 481 (5.8%) were positive. The positivity rate of HEV RNA was much higher for the HEV antigen positive sera (40.1%) than the anti-HEV antibody positive (1.4%) or negative (1.1%), antigen negative samples. Sixteen of the 28 samples were positive for HEV RNA using nested RT-PCR and their products were cloned and sequenced. These 16 isolates belonged to HEV genotype 4, including 12 that did not belong to any subtype of HEV genotype 4 reported previously. Thus, the infection rate of HEV in pigs is high and the HEV antigen has a close relationship with HEV RNA. The HEV genotype infecting the pigs was genotype 4 and a novel subtype may exist in Hunan province.