Research snapshot: MRSA appears not as problematic in US swine as originally thought

Since 2004, when methicillin-resistant Staphylococcus aureus (MRSA) was first discovered in European swine, there has been a focus on how livestock-associated MRSA effects the European population. Although first detected in US pigs in 2007, relatively little information has been available about MRSA in US pigs.

Peter Davies, Ph.D., professor in the University of Minnesota College of Veterinary Medicine, in partnership with scientists from the USDA National Animal Disease Center and the Iowa State University College of Veterinary Medicine, conducted two studies on MRSA in relation to US pigs and the people who work with them.

According to the studies, MRSA appears to be much less common in US pig herds than anticipated, but more varied than in pigs in Europe. Both the main European variety of MRSA and another variety that has up to now only been seen in North America showed little genetic capability to cause infections in humans.

The first study looked at this North American variant of MRSA found in Iowa swine and in veterinarians in several states. The team studied veterinarians rather than farmers because farmers work with the same swine herd. Veterinarians travel from farm to farm and are exposed to many different herds, which gave researchers a better picture of what people are exposed to in the industry.

The team found that MRSA bacteria appeared to have diminished capability to cause human disease compared with similar variants that caused disease in the human population. When MRSA adapts to the pig, it seems to lose some of the material necessary to cause infections in people.

“As far as we can tell, there is little or no impact on public health,” Davies said. “No serious infections have been seen in swine workers or veterinarians.”

The second study looked at the prominence of MRSA in US swine herds. Other than the control group, no herds tested positive for MRSA, suggesting that MRSA prevalence in US swine herds is no more than 10 percent. This is noticeably lower than in Europe, where some countries see an estimated 70 percent of swine herds infected.

While the research is positive for US swine herd owners and veterinarians, Davies hopes more research will be done to better understand the potential risks of MRSA-infected swine herds on people in the US.
“US pigs certainly have MRSA, it’s just not widespread at this point,” Davies said. “That doesn’t mean it wont change.”

You can find the published studies at the links below:

Comparative Prevalence of Immune Evasion Complex Genes Associated with β-Hemolysin Converting Bacteriophages in MRSA ST5 Isolates from Swine, Swine Facilities, Humans with Swine Contact, and Humans with No Swine Contact

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