Diarrhea is a common disorder in pigs, and associated dehydration is a leading cause of mortality among piglets, causing substantial economic losses. Studies have found that the etiology of diarrhea is varied, including multiple viral, bacterial, and parasitic pathogens, but viruses such as porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), rotavirus (RV) and other enteroviruses (EV), are the predominant factors in most cases. Repeated outbreaks have also been reported on farms in which piglets had been immunized by vaccines targeting these viruses. Recently, newly emerging viruses, such as mammalian orthoreovirus (MRV), which can cause diarrhea alone or in co-infections with other known pathogens, have been of great concern in China, South Korea, USA and Europe. Few researches on MRV, especially its epidemiological survey and analysis have been carried out in China.
In order to understand the epidemicity of MRV in China, molecular and seroepidemiological survey of MRV type 3 in diarrheic pigs from five provinces of east China was performed in this study. A nested reverse transcription-polymerase chain reaction (RT-PCR) method was designed to target the L1 gene. A total of 224 diarrheic fecal samples collected from 58 pig farms from Zhejiang, Jiangxi, Shandong, Henan and Heilongjiang provinces in 2013—2014 were examined by this method. Our data revealed that porcine orthoreovirus was present in 147 of 224 (65.6％) diarrheic porcine fecal samples obtained from 55 of 58 (94.8％) pig farms. At the same time, a neutralization test as well as an indirect enzyme-linked immunosorbent assay (ELISA) with a purified σ1 protein as a coat antigen was developed. The neutralization antibody levels and the anti-σ1 IgG antibody levels of 37 serum samples were determined. A good linear relationship between the anti-σ1 antibodies and virus neutralization (VN) antibodies was observed, demonstrating the correlation between them. Then the σ1- based ELISA was applied to the subsequent seroepidemiological survey of MRV3. A total of 262 serum samples collected from the sows, one- week-old piglets as well as three-week-old weaning piglets in 2015—2016 were tested. The result showed these samples had a high positive rate of anti-MRV IgG (84.4％).
Overall, the preliminary results suggest that MRVs are widespread in piglets from five provinces of east China and may collectively contribute to the enteric disease along with other porcine pathogens.