Rotaviruses seem to be everywhere across U.S. pig farms. That’s why understanding how they spread, change and contribute to disease is essential for improving herd health. A recent study investigated the potential role of porcine rotaviruses in swine respiratory disease.
Although rotavirus species A and C are among the most common causes of diarrhea in young pigs, new evidence suggests some strains may also affect the porcine respiratory tract. This study found that high on-farm prevalence of rotaviruses A (RVA) and C (RVC) has a strong association with diarrheal disease. Researchers did not see evidence of RVC involvement in the porcine respiratory disease complex; however, researchers say RVA may be emerging as a potential respiratory pathogen of suckling piglets.
What Do Producers and Veterinarians Need to Know?
Anastasia Vlasova of The Ohio State University led this study funded by the Swine Health Information Center (SHIC) and conducted on six swine farms in Ohio (two research farms and four commercial farms). Results demonstrated that RVA and RVC were present on all six farms. The prevalence of different rotaviruses varied greatly between different farms (A: 67-100%; C: 7-56%). Overall, 88% and 29% of piglets were positive for RVA and RVC, respectively. Consistent with prior research, the highest RVA prevalence/viral loads were found in diarrheic weaned piglets on most farms. However, suckling piglets with respiratory signs from farm 6 and diarrheic suckling piglets from farm 5 also had increased RVA loads, SHIC reports.
One of the most important findings was that suckling piglets with respiratory signs from farm 6 shed either more RVA nasally or comparable levels to those shed with feces, while all other piglets on all farms had consistently higher fecal shedding of the virus. The study points out this could be attributed to the genetic diversity of the circulating RVA strains, which will be explored further.
Other findings include:
- Researchers also confirmed RVA presence in various samples, including samples from the respiratory tract of 12 out of 16 dead suckling piglets from farm 2.
- RVC shedding was detected either at a very low level, suggesting no ongoing outbreak on farms 2 and 5, or at higher levels in suckling piglets with diarrhea on farms 1 and 4.
- Farm 6 was an outlier, where RVC loads were the highest in weaned piglets exhibiting diarrhea.
- On farm 3 only, healthy weaned piglets had the highest loads of RVA and RVC.
- Farm 4 had the lowest overall prevalence of RVA, which coincided with the highest prevalence of RVC. SHIC notes it is unclear whether the heightened biosecurity measures in place at the time of sample collection—implemented due to an ongoing outbreak of highly pathogenic influenza A virus in nearby poultry farms—contributed to this outcome.
Rotavirus and Other Pathogen Interactions
Screening for other respiratory and enteric pathogens did not reveal any strong associations between individual pathogens and increased prevalence of rotavirus infections. Selected representative RVA and RVC positive (paired nasal and rectal swab) samples from suckling and weaned piglets from different farms will undergo next generation sequencing.
In addition, researchers selected representative samples from different farms with RVA and RVC positive piglets with and without diarrhea or respiratory signs to determine whether a specific metagenomic composition can protect or predispose piglets to the rotavirus-associated illness.
Researchers said the remarkably high overall prevalence of RVA on all farms suggests it may utilize other transmission routes (e.g. airborne) in addition to fecal-oral/contact.
“Overall, the current findings highlight that RVA and RVC are ubiquitous pathogens impacting the US swine industry with potential emerging clinical presentations,” SHIC reports. “The contrasting mechanisms associated with their pathogenesis and spread need to be studied in-depth to inform and update existing control strategies.”
