Evidence of natural transmission of group A rotavirus between domestic pigs and wild boars (Sus scrofa) in Japan

Group A rotaviruses (RVAs) are a major cause of acute dehydrating diarrhea in infants and young animals worldwide. RVAs have also been detected in several wild and zoo animals, indicating wide susceptibility of wild animals. However, the role of wild animals in the infection cycle of RVAs is unclear. Wild boars are indigenous in many countries in the world. Japanese wild boars (Sus scrofa leucomystax) have been migrating close to human habitats in Japan, indicating the possibility of natural transmission between domestic animals or humans and wild boars. We investigated infection of RVAs in wild boars in Japan to identify types of RVAs infecting wild animals. We obtained stool samples from 90 wild boars and detected a VP4 gene of RVAs by RT-semi-nested PCR. RVAs were detected in samples from four of the 90 wild boars. Nucleotide analyses of VP7 and VP4 genes revealed that the four strains belong to G9P[23], G4P[23], G9P[13] and G4P[6], suggesting a relation to porcine and human RVAs. We therefore characterized RVAs circulating among domestic pigs living in the same area as the wild boars. We collected stool samples from 82 domestic pigs. RVAs were detected in samples from 49 of the 82 domestic pigs. Phylogenetic and similarity analyses provided evidence for natural transmission between domestic pigs and wild boars. The results also suggested that natural reassortment events occurred before or after transmission between domestic pigs and wild boars. Our findings indicate the possibility that RVAs circulate among wild animals, humans and domestic animals in nature.