Genetic and serological surveillance for non-primate hepacivirus in horses in Japan

Non-primate hepacivirus (NPHV) is a recently discovered homolog of the hepatitis C virus in horses. The frequency and distribution of NPHV infections among horses in Japan is unknown. In this study, serum samples from 453 horses across Japan were screened for NPHV RNA using real-time RT-PCR and anti-nonstructural 3 protein (NS3) antibodies using the Gaussia luciferase immunoprecipitation system assay. In order to monitor the course of NPHV infection in horses, we examined 31 stored samples (9 adult horses and 22 young horses) obtained one year ago and compared the results to the recent data. Stored sera from 7 mare-foal pairs were also examined. The NS3 region sequences of 14 NPHV strains from NPHV RNA positive serum samples were determined and analyzed phylogenically. Of the 453 serum samples tested, 33.55% were positive for anti-NS3 antibody and 13.68% were positive for NPHV RNA. We found a higher rate of NPHV RNA detection in serum obtained from young horses (1-2 years of age) than that of adults, in two geographically distinct areas. We observed higher variation in the course of infection over one year in young horses than in adult horses. The foals were infected with NPHV after the weaning period. Phylogenic analysis revealed that while NPHV NS3 genes isolated in Japan clustered with sequences previously classified as NPHV, but the genetic diversity of the Japanese NPHV strains we detected was not correlated with their geographic origin. In conclusion, Japanese horses exhibit a high prevalence of NPHV. Young age appears to be a risk factor for such viral infection in Japan, although the infectious route was not determined.