Current status of hepatitis E virus infection at a rhesus monkey farm in China

Rhesus and several other species of monkeys are susceptible to genotypes of hepatitis E virus (HEV), and these species are thus commonly used as animal models for experimental HEV infection. However, information regarding HEV infection in monkeys in nature or at monkey farms is limited. To investigate the status of HEV infection in rhesus monkeys at farms, we collected 548 serum and 48 fecal samples from a rhesus monkey farm in China, and analyzed their levels of anti-HEV IgG antibodies and HEV RNAs. An enzyme-linked immunosorbent assay using genotype 3 HEV-like particles as antigen revealed anti-HEV IgG-positivity in 388 (70.8%) monkeys. The antibody-positive rates in the 1-year-old and 2-year-old monkeys were significantly lower than those in monkeys >3 years old. The antibody-positive rate was greatly increased from 7.4% in the 2-year-old monkeys to 100% in the 3-year-olds, suggesting that the latter received HEV infection at a high frequency. HEV RNA was detected in one of 88 sera from 1- and 2-year-old monkeys and 10 of 48 fecal specimens from 3-year-old monkeys by reverse transcription-polymerase chain reaction. Phylogenetic analyses revealed that the HEV strain RmKM15 was present in a serum sample that belonged to subtype 4b in genotype 4, whereas 10 strains detected in the fecal specimens belonged to subtype 4 h, suggesting that two genetically different strains were circulating at the farm. However, no significant clinical signs were observed in these monkeys. Further studies are required to identify the source of infection and to evaluate the pathogenicity of HEV in rhesus monkeys.