Nonhuman Primate Models of Hepatitis A Virus and Hepatitis E Virus Infections

Abstract

Although phylogenetically unrelated, human hepatitis viruses share an exclusive or near exclusive tropism for replication in differentiated hepatocytes. This narrow tissue tropism may contribute to the restriction of the host ranges of these viruses to relatively few host species, mostly nonhuman primates. Nonhuman primate models thus figure prominently in our current understanding of the replication and pathogenesis of these viruses, including the enterically transmitted hepatitis A virus (HAV) and hepatitis E virus (HEV), and have also played major roles in vaccine development. This review draws comparisons of HAV and HEV infection from studies conducted in nonhuman primates, and describes how such studies have contributed to our current understanding of the biology of these viruses.

Figure 1.

Phylogenetic relationships of nonhuman primates (NHPs) used commonly for studies of hepatitis viruses and known susceptibility to specific viruses. Commonly accepted dates of species divergence are shown (mya = millions of years ago). Note that only mice with genetic deficiencies in innate immune signaling pathways, and not wild-type mice, are susceptible to hepatitis A virus (HAV), and that hepatitis B virus (HBV) infections in baboons may be restricted to certain species (Chacma baboons). All of the great apes, Old World, and New World NHPs shown here (with the possible exception of squirrel monkeys) have been found to have naturally acquired antibodies reactive to HAV (Deinhardt and Deinhardt 1984), and thus may be susceptible to infection with the virus. A broader range of NHP species than those shown here is also likely to be susceptible to hepatitis E virus (HEV) infection.

Figure 2.

Acute hepatitis A virus (HAV) infection in a chimpanzee (Pan troglodytes). (A) Percutaneous liver biopsy taken 21 days after intravenous (i.v.) inoculation of HM175 virus. There is moderate portal inflammation with hemosiderin-laden macrophages and early piecemeal necrosis with erosion of the limiting plate. (B) Acute HAV infection in a chimpanzee inoculated i.v. with a human fecal extract containing the MS1 strain of HAV. Fecal virus shedding detected by solid-phase radioimmunossay (bottom panel) preceded maximal liver enzyme elevation and appearance of anti-HAV antibodies detected in a blocking immunoassay. Total serum bilirubin was 0.1 mg/dL at peak elevation of alanine aminotransferase (ALT) γ-glutamyl transpeptidase (GGTP) elevations. This study was performed in 1978 at the Laboratory of Experimental Medicine and Surgery in Primates.

Figure 3.

Hepatitis A virus (HAV) infection in chimpanzees following intravenous (i.v.) viral challenge. (A) HAV RNA detection (green) by fluorescent in situ hybridization (FISH) in biopsies of liver from chimpanzee 4x0395 14 weeks before (left) and 3 weeks (right) after i.v. inoculation of HM175 virus. At 3 weeks, abundant viral RNA is present within the cytoplasm of numerous hepatocytes surrounding an inflammatory infiltrate. (Image courtesy of David R. McGivern.) (B) Persistence of intrahepatic HAV RNA following acute infection in a chimpanzee (4x0293). HAV RNA was quantified in serum (red line), liver (green line), and feces (blue line) by RT-qPCR. Serum alanine aminotransferase (ALT) levels are indicated by the gray shaded area. IgM anti-HAV and total anti-HAV are shown as positive or negative (+ or −) at the top of the panel. (From Lanford et al. 2011a; adapted, with permission, from the authors.)

Figure 4.

Acute hepatitis A virus (HAV) infection in a New World owl monkey (Aotus trivirgatus). The animal was one of six infected by intravenous inoculation of a cell-culture-adapted virus permitting quantitation of infectious virus in feces and serum using a modified plaque assay method (Lemon et al. 1990). The challenge virus was a neutralization escape mutant with an amino acid substitution at residue 70 of VP3 that confers escape from a neutralizing monoclonal antibody; by day 12 of the infection, this virus was replaced with revertant virus with wild-type capsid sequence. Note that antibody and infectious virus cocirculated in blood for an extended period (see text for additional details). “RFU” = radioimmunofocus-forming unit.

Figure 5.

Course of acute hepatitis E in a rhesus macaque. A rhesus macaque was challenged intravenously with 10⁷ RNA genome equivalents of a hepatitis E virus (HEV) genotype gt3 strain designated Kernow (kindly provided by Dr. S. Emerson). HEV RNA genome titers in serum and feces were determined by RT-qPCR. Antibodies (IgM and IgG) against the HEV open reading frame 2 (ORF2) capsid were measured by ELISA assay.

Figure 6.

Hepatitis E virus (HEV) infection in macaque species and chimpanzees. (A) Peak ALT values in cynomolgus and rhesus macaques and chimpanzees infected with the same dose of a genotype (gt)1 HEV strain. Geometric mean peak ALT titers were significantly higher in both macaque species when compared with the chimpanzees. (B) The time to peak ALT was shorter in rhesus macaques infected with high versus low doses of an HEV gt1 strain. The study also established an inverse relationship between HEV challenge dose and the time to seroconversion (not shown). (C) Peak ALT values were significantly higher in rhesus macaques infected with gt1 and gt2 viruses when compared with a gt3 strain. (Adapted from Purcell et al. 2013.)