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