Experimental infection of rabbits with rabbit and genotypes 1 and 4 hepatitis E viruses

Abstract

Background: A recent study provided evidence that farmed rabbits in China harbor a novel hepatitis E virus (HEV) genotype. Although the rabbit HEV isolate had 77-79% nucleotide identity to the mammalian HEV genotypes 1 to 4, their genomic organization is very similar. Since rabbits are used widely experimentally, including as models of infection, we investigated whether they constitute an appropriate animal model for human HEV infection.

Methods: Forty-two SPF rabbits were divided randomly into eleven groups and inoculated with six different isolates of rabbit HEV, two different doses of a second-passage rabbit HEV, and with genotype 1 and 4 HEV. Sera and feces were collected weekly after inoculation. HEV antigen, RNA, antibody and alanine aminotransferase in sera and HEV RNA in feces were detected. The liver samples were collected during necropsy subject to histopathological examination.

Findings: Rabbits inoculated with rabbit HEV became infected with HEV, with viremia, fecal virus shedding and high serum levels of viral antigens, and developed hepatitis, with elevation of the liver enzyme, ALT. The severity of disease corresponded to the infectious dose (genome equivalents), with the most severe hepatic disease caused by strain GDC54-18. However, only two of nine rabbits infected with HEV genotype 4, and none infected with genotype 1, developed hepatitis although six of nine rabbits inoculated with the genotype 1 HEV and in all rabbits inoculated with the genotype 4 HEV seroconverted to be positive for anti-HEV IgG antibody by 14 weeks post-inoculation.

Conclusions: These data indicate that rabbits are an appropriate model for rabbit HEV infection but are not likely to be useful for the study of human HEV. The rabbit HEV infection of rabbits may provide an appropriate parallel animal model to study HEV pathogenesis.

Figure 1. Time course of seroconversion to anti-HEV in SPF rabbits inoculated with different virus isolates.

(A) The mean ELISA signal-to-cutoff (S/CO) values for all rabbits from each group at each week post-inoculation are plotted. (B) All rabbits from groups 3 to 8 inoculated with the non-passaged HEV are named R1ST and the combination of groups RH1 and RH4 are named RH.

Figure 2. Time course of serological appearance of HEV antigens in inoculated SPF rabbits.

(A) The weekly mean ELISA signal-to-cutoff (S/CO) values for all rabbits from each group are plotted. (B) All rabbits from groups 3 to 8 inoculated with the non-passaged HEV are named R1ST and the combination of groups RH1 and RH4 are named RH.

Figure 3. Levels of the lalanine aminotransferase (ALT) in sera from inoculated and control rabbits.

(A) The mean ALT values of all rabbits from each group at each week post-inoculation are plotted. (B) All rabbits from groups 3 to 8 inoculated with the non-passaged rabbit HEV are named R1ST and the combination of groups RH1 and RH4 are named RH.

Figure 4. Pathological signs of HEV infection in hematoxylin and eosin stained liver sections.

(A & B) Liver sections from a group 2GDC54-18 rabbit showing localized extensive hepatocellular necrosis (magnification 10× and 20×, respectively). (C) Liver section from a group RH4 rabbit showing irregularly distributed multifocal lymphohistiocytic infiltrates (20×). (D) Liver section from a control rabbit showing no visible pathological signs of HEV infection (20×).