High Prevalence of Hepatitis E Virus Infection in Imported Cynomolgus Monkeys in Japan

Cynomolgus monkeys are important experimental animals for hepatitis E virus (HEV) infection. In Japan, cynomolgus monkeys are mainly imported from Asian countries for use at animal facilities and institutions. However, the status of HEV infection in cynomolgus monkeys remains unclear. Overall, 187 pairs of serum and fecal samples were collected from cynomolgus monkeys (Macaca fascicularis) imported from China and Cambodia to detect anti-HEV immunoglobulin (Ig) G and IgM antibodies, as well as HEV RNA. Based on an enzyme-linked immunosorbent assay using HEV-like particles derived from genotype 3 HEV as the antigen, 183 of 187 (97.9%) and 102 of 187 (54.5%) samples tested positive for anti-HEV IgG and IgM antibodies, respectively. In contrast, all 45 serum samples collected from cynomolgus monkeys bred and grown at the Tsukuba Primate Research Center, Japan tested negative for both antibodies. However, real-time quantitative reverse transcription polymerase chain reaction detected no HEV RNA in any of the 187 serum and fecal samples. These results strongly indicated that HEV infection is common in imported cynomolgus monkeys. A source of HEV-free monkeys for HEV studies is urgently needed.