Researchers Study Antibiotic-Resistant Staph in Horses, Humans

The Canadian Medical Association Journal recently reported that cases of an antibiotic-resistant strain of Staphylococcus aureus were on the rise in Canada. As public health officials there focus on minimizing the spread of infections in humans, veterinary health researchers have spent the past few years studying the disease and how it is transmitted between humans and horses.

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium that can cause a range of conditions from lesions to pneumonia. Methicillin had been the primary antibiotic treatment for S. aureus until a strain of the bacterium mutated in response to widespread use of the drug.

In a 2005 address before the American College of Veterinary Internal Medicine (ACVIM), Scott Weese, DVM, SVSc, Dipl. ACIVM, an associate professor at the University of Guelph’s Ontario Veterinary College, reported MRSA can be passed from a humans carrying it in their nasal passages to immune-compromised horses in a clinical setting. In further research, Weese studied horses on farms where MRSA infections were reported to learn how the strain was spread in a nonclinical or “community-assisted” (CA) setting.

Since then, researchers in the United States, including those from Colorado State University, Oklahoma State University, Michigan State University, and the University of Pennsylvania (Penn) began tracking MRSA cases to learn more.

“We discovered that there was a strain of community-assisted MRSA that survives well in a horse's nose,” said Helen Aceto, PhD, VMD, director of biosecurity and assistant professor of epidemiology at Penn's School of Veterinary Medicine. “The strain also survives in humans’ noses."

Aceto said the infection generally disappears on its own, once infected horses are isolated from noninfected ones, although intractable cases still require antibiotic treatment.

Since she’s been tracking CA-MRSA in horses at Penn's New Bolton Center, Aceto says she hasn't seen an explosion in MRSA cases. The greatest number was nine in a single year, and the smallest number of cases was just one.

Even so, researchers have established policies to carry out the voluntary testing of humans who work with horses in clinical and farm settings where MRSA is present. And although not all horses and humans who test positive for CA-MRSA become ill, understanding MRSA and its transmission is crucial from a public health standpoint.

“It’s not something that we need to be overly concerned about,” Aceto said, “but it’s also not something we want to let get out of hand.”

About the Author

Pat Raia

Pat Raia is a veteran journalist who enjoys covering equine welfare, industry, and news. In her spare time, she enjoys riding her Tennessee Walking Horse, Sonny.

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