Distinct disease features of acute and persistent genotype 3 hepatitis E virus infection in immunocompetent and immunosuppressed Mongolian gerbils

Hepatitis E virus (HEV) causes self-limited acute hepatitis in immunocompetent individuals and can establish chronic infection in solid organ transplant recipients taking immunosuppressive drugs. A well characterized small animal model is needed to understand HEV pathogenesis. In this study, we established a robust model to study acute and persistent HEV infection using Mongolian gerbils (Meriones unguiculatus) with or without immunosuppression. Gerbils were implanted subcutaneously with continuous release tacrolimus pellet to induce immunosuppression. Gerbils with or without tacrolimus treatment were inoculated with HEV intraperitoneally. Viremia, fecal virus shedding, serum antibody and ALT levels, liver histopathological lesions, hepatocyte apoptosis, and liver macrophage distribution were assessed. Mild to moderate self-limited hepatitis and IgM and IgG antibody responses against HEV ORF2 were observed in immunocompetent gerbils. Levels of HEV-specific IgM responses were higher and lasted longer in immunocompetent gerbils with higher peak viremia. Persistent viremia and fecal virus shedding with either weak, or absent HEV antibody levels were seen in immunosuppressed gerbils. Following HEV infection, serum ALT levels were increased, with lower and delayed peaks observed in immunosuppressed compared to immunocompetent gerbils. In immunocompetent gerbils, foci of apoptotic hepatocytes were detected that were distributed with inflammatory infiltrates containing CD68+ macrophages. However, these foci were absent in immunosuppressed gerbils. The immunosuppressed gerbils showed no inflammation with no increase in CD68+ macrophages despite high virus replication in liver. Our findings suggest adaptive immune responses are necessary for inducing hepatocyte apoptosis, CD68+ macrophage recruitment, and inflammatory cell infiltration in response to HEV infection. Our studies show that Mongolian gerbils provide a promising model to study pathogenesis during acute and persistent HEV infection. Hepatitis due to genotype-3 E virus (HEV) is a zoonotic disease that is acquired by consumption of undercooked meat or offal from infected animals, typically pigs. HEV usually causes acute, self-limited hepatitis but in immunosuppressed persons, such as solid organ transplant recipients, it can establish chronic infection, associated with rapid liver fibrosis progression. Since HEV does not infect mice or other small animals, studies on disease pathogenesis are limited. In this study, we compared HEV kinetics, antibody responses, and liver disease in Mongolian gerbils with or without immunosuppression induced by the drug tacrolimus. In immunocompetent gerbils with acute infection, we observed mild hepatitis with foci of apoptotic hepatocytes and activated macrophages surrounding HEV-infected cells. In contrast, immunosuppressed gerbils failed to clear HEV infection and showed approximately 10-fold higher viral loads in serum and feces. Of note, despite higher virus replication in the liver, hepatocyte apoptosis and inflammation were not observed in the immunosuppressed group, suggesting that the liver damage in acute hepatitis E is immune-mediated. The absence of inflammation and apoptosis in livers of immunosuppressed gerbils with persistent, high-level HEV replication suggests that the progression to fibrosis in immunosuppressed patients is due to underlying factors other than HEV.