15 July 2025

2 minute read

By: Chris Wright

North America

Editor's note: The following is from a presentation by W. Ma and colleagues at the University of Missouri and Kansas State University during the 2024 North American PRRS Symposium. 

Mammalian orthoreovirus (MRV) infects multiple mammalian species including humans. A US Midwest swine farm with approximately 1,000 3-month-old pigs experienced an event, in which more than 300 pigs showed neurological signs, like “down and peddling”, with approximately 40% mortality. A novel MRV was isolated from the diseased pigs.

Sequence and phylogenetic analysis revealed that the isolate was a reassortant virus containing viral gene segments from three MRV serotypes that infect humans, bovines and swine. The M2 and S1 segment of the isolate showed 94% and 92% nucleotide similarity to the M2 of the MRV2 D5/Jones and the S1 of the MRV1 C/Bovine/Indiana/MRV00304/2014, respectively; the remaining eight segments displayed 93%–95% nucleotide similarity to those of the MRV3 FS-03/Porcine/USA/2014.

Pig studies showed that both MRV-infected and native contact pigs displayed fever, diarrhea and nasal discharge. MRV RNA was detected in different intestinal locations of both infected and contact pigs, indicating that the MRV isolate is pathogenic and transmissible in pigs. Seroconversion was also observed in experimentally infected pigs.

A prevalence study on more than 180 swine serum samples collected from two states without the disease revealed 40%–52% positives to MRV. All results warrant the necessity to monitor MRV epidemiology and reassortment as the MRV could be an important pathogen for the swine industry and a novel MRV might emerge to threaten animal and public health.