Comparative pathogenesis of infection of pigs with hepatitis E viruses recovered from a pig and a human

Abstract

Specific-pathogen-free pigs were inoculated with one of two hepatitis E viruses (HEV) (one recovered from a pig and the other from a human) to study the relative pathogenesis of the two viruses in swine. Fifty-four pigs were randomly assigned to three groups. Seventeen pigs in group 1 served as uninoculated controls, 18 pigs in group 2 were intravenously inoculated with the swine HEV recovered from a pig in the United States, and 19 pigs in group 3 were intravenously inoculated with the US-2 strain of human HEV recovered from a hepatitis patient in the United States. Two to four pigs from each group were necropsied at 3, 7, 14, 20, 27, or 55 days postinoculation (DPI). Evidence of clinical disease or elevation of liver enzymes or bilirubin was not found in pigs from any of the three groups. Enlarged hepatic and mesenteric lymph nodes were observed in both HEV-inoculated groups. Multifocal lymphoplasmacytic hepatitis was observed in 9 of 17, 15 of 18, and 16 of 19 pigs in groups 1 to 3, respectively. Focal hepatocellular necrosis was observed in 5 of 17, 10 of 18, and 13 of 19 pigs in groups 1 to 3, respectively. Hepatitis lesions were very mild in group 1 pigs, mild to moderate in group 2 pigs, and moderate to severe in group 3 pigs. Hepatic inflammation and hepatocellular necrosis peaked in severity at 20 DPI and were still moderately severe at 55 DPI in the group inoculated with human HEV. Hepatitis lesions were absent or nearly resolved by 55 DPI in the swine-HEV-inoculated pigs. All HEV-inoculated pigs seroconverted to anti-HEV immunoglobulin G. HEV RNA was detected by reverse transcriptase PCR in feces, liver tissue, and bile of pigs in both HEV-inoculated groups from 3 to 27 DPI. Based on evaluation of microscopic lesions, the US-2 strain of human HEV induced more severe and persistent hepatic lesions in pigs than did swine HEV. Pig livers or cells from the livers of HEV-infected pigs may represent a risk for transmission of HEV from pigs to human xenograft recipients. Since HEV was shed in the feces of infected pigs, exposure to feces from infected pigs represents a risk for transmission of HEV, and pigs should be considered a reservoir for HEV.

FIG. 1

Liver of a sham-inoculated control pig (14 DPI) with rare lymphoplasmacytic infiltrates in hepatic sinusoids. Hematoxylin and eosin staining was performed.

FIG. 2

Liver of a pig i.v. inoculated with HEV recovered from a U.S. pig. There is mild focal infiltration of lymphocytes, plasma cells, and macrophages and mild diffuse inflammation in hepatic sinusoids at 14 DPI. Hepatocytes are mildly swollen and vacuolated. Hematoxylin and eosin staining was performed.

FIG. 3

Liver of a pig i.v. inoculated with HEV recovered from a human hepatitis patient in the U.S. There is severe lymphoplasmacytic and histiocytic hepatitis and severe vacuolar degeneration and swelling of hepatocytes at 14 DPI. Hematoxylin and eosin staining was performed.

FIG. 4

Liver of the same pig as that shown in Fig. 3. Note the individual necrotic hepatocytes (arrow). Hematoxylin and eosin staining was performed.