Risk of hepatitis E virus infection associated with urban invasion of wild Deer (Cervus nippon yesoensis) in Hokkaido, Japan

The number of hepatitis E cases in Japan is reported to be high in Hokkaido, where small outbreaks, mainly of hepatitis E virus (HEV) genotype 3, have been reported over the past 15 years. In Hokkaido, the wild deer population is increasing and is found in mountainous areas and urban areas, where civilians mix with wild deer. Since cases of HEV transmission from deer to humans have been reported, this study aimed to determine the prevalence of the hepatitis E virus in Hokkaido, Japan, due to the increasing urbanization of the deer habitat. The study examined the detection of HEV RNA in the liver, and the distribution of HEV RNA prevalence among 153 wild deer was significantly higher in deer captured in urban areas (42.7%) than in mountainous areas (17.2%). HEV-ORF2 sequencing of positive deer revealed that all sequences belonged to the same cluster in genotype 3. The same strain of HEV was circulating among the deer. Relative risk (RR) was analyzed for the risk of HEV infection in different deer capture areas in urban and mountain areas, with an RR value of 2.479 and a 95% confidence interval of 1.089 - 5.646, and a chi-square test (×2 test) result of 0.01. The results suggest that these deer may be a risk factor for zoonotic disease in human habitats.