Study finds MRV, PAdV present but low risk in U.S. pigs

The Swine Health Information Center funded a study to examine whether mammalian orthoreovirus and porcine adenovirus are present in U.S. swine herds and whether they pose health risks. Led by Wenjun Ma, University of Missouri, the study suggests that MRV and PAdV can infect pigs and contribute to general enteric disease but that these viruses are not associated with severe or unique clinical signs. These findings suggest that both viruses circulate in swine populations, with evidence pointing toward intestinal shedding or prior exposure rather than widespread active disease in routine tissue submissions. For producers and their veterinarians, this study helps interpret diagnostic findings on MRV or PAdV, enabling more informed herd health decisions.

Emerging and re-emerging viral pathogens remain an ongoing threat to the U.S. swine industry, and undiagnosed disease outbreaks continue to highlight important gaps in pathogen surveillance and characterization. Although MRV and PAdV have been reported in pigs in other countries globally, contemporary data for U.S. swine populations are limited. Previous research suggests that MRV and PAdV may contribute to clinically significant disease in swine, yet their prevalence, epidemiology, pathogenic potential and impact on production remain poorly defined. This project was designed to address two objectives: 1) define the prevalence and epidemiology of MRV and PAdV in US swine herds and 2) determine the pathogenicity and transmissibility of MRV and PAdV in weaned pigs, including the potential contribution of co-infection to clinical disease.

To provide a clearer picture of how common these viruses may be and whether they pose a health risk, lung, intestinal, blood, and fecal samples were tested for evidence of MRV and PAdV. A total of 794 swine tissue samples collected through diagnostic laboratories were screened, including eight intestinal samples and 783 lung samples from 18 US states (North Carolina, Oklahoma, Minnesota, Indiana, Illinois, Missouri, Montana, Arkansas, California, South Dakota and Kansas), as well as three lung samples from Mexico. RT-qPCR results showed that 29 of 786 (3.69%) swine lung tissue samples were positive for MRV and that one of eight (12.5%) intestinal samples were positive for MRV. However, only one virus was isolated from one RT-qPCR -positive lung sample, and not from other RT-qPCR-positive samples.