Prevalence and genomic characteristics of a novel reassortment mammalian orthoreovirus type 2 in diarrhea piglets in Sichuan, China.

Mammalian orthoreovirus (MRV), which can infect almost all mammals, is a zoonotic virus. In this study, six strains of type 2 MRV (MRV2) were isolated from 7 diarrhea piglets from a farm that had an outbreak of diarrhea in piglets in 2018, which tested negative for porcine epidemic diarrhea virus (PEDV), porcine transmissible gastroenteritis virus (TGEV), porcine deltacoronavirus (PDCoV), and porcine group A rotavirus (RAV). The MRV2 isolate infected neonatal piglets, in which it induced severe diarrhea, while the virus was detected in multiple organs of piglets. Moreover, the complete genome of an MRV2 isolate was obtained, which was a novel reassortant MRV strain of human MRV, porcine MRV, chamois MRV, bat MRV, and mink MRV based on the nucleotide identity and phylogenetic tree. The S1 gene of isolate had eight unique amino acid mutations compared with available MRV2 S1 in the GenBank. To investigate the prevalence of this MRV2, 78 samples of diarrhea feces were collected from 10 pig farms in seven regions of Sichuan province. The obtained results showed that the positive rate of samples was 14% (11/78), and positive rate of farms was 60% (6/10), while the amplified fragments shared the identical amino acid mutations with the isolated strain, thus suggesting that this MRV2 strain was already prevalent in Sichuan province. The present study was first to isolate a pig-derived type 2 MRV strain in China, obtaining the complete genome of this strain, which furthers our understanding of the MRV2 epidemic and evolution.