Cross-species infection of specific-pathogen-free pigs by a genotype 4 strain of human hepatitis E virus

Abstract

Hepatitis E virus (HEV) is an important pathogen. The animal strain of HEV, swine HEV, is related to human HEV. The genotype 3 swine HEV can infect humans and genotype 3 human HEV can infect pigs. The genotype 4 swine and human HEV strains are genetically related, but it is unknown whether genotype 4 human HEV can infect pigs. A swine bioassay was utilized in this study to determine whether genotype 4 human HEV can infect pigs. Fifteen, 4-week-old, specific-pathogen-free pigs were divided into three groups of five each. Group 1 pigs were each inoculated intravenously with PBS buffer as negative controls, group 2 pigs similarly with genotype 3 human HEV (strain US-2), and group 3 pigs similarly with genotype 4 human HEV (strain TW6196E). Serum and fecal samples were collected at 0, 7, 14, 21, 28, 35, 42, 49, and 56 days postinoculation (dpi) and tested for evidence of HEV infection. All pigs were necropsied at 56 dpi. As expected, the negative control pigs remained negative. The positive control pigs inoculated with genotype 3 human HEV all became infected as evidenced by detection of HEV antibodies, viremia and fecal virus shedding. All five pigs in group 3 inoculated with genotype 4 human HEV also became infected: fecal virus shedding and viremia were detected variably from 7 to 56 dpi, and seroconversion occurred by 28 dpi. The data indicated that genotype 4 human HEV has an expanded host range, and the results have important implications for understanding the natural history and zoonosis of HEV.

FIG. 1

Seroconversion to IgG anti-HEV in HEV-inoculated and control pigs. Panel A, pigs inoculated with sterile phosphate buffered saline (PBS) as negative controls (group 1); Panel B, pigs inoculated with a genotype 3 human HEV (strain US-2) as positive controls (group 2); Panel C, pigs inoculated with a genotype 4 human HEV (strain TW6196E) as the experimental group (group 3). The ELISA cutoff OD value is 0.30.

FIG. 2

Average titers of HEV RNA in feces (expressed as log copies per mg of feces) from all five pigs in each group at the indicated days post-inoculation (dpi) during the first 4 weeks of infection. The open bars represent pigs inoculated with the genotype 3 human HEV (Strain US-2) and the filled bars represent pigs inoculated with genotype 4 human HEV (Strain TW6196E). The error bars represent ± standard deviation.