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Researchers investigate troubling bacterium threatening horses and humansAugust 2003

A complicated and transferable bacterial illness has brought equine and human health researchers together to root out its cause and stop its spread.

Dr. Scott Weese, Clinical Studies, and Marie Archambault, an Animal Health Laboratory bacteriologist, are working with Don Low, chief of microbiology at Mount Sinai Hospital, and Hani Dick, a bacteriologist with Vita-Tech Veterinary Laboratories, to research characteristics of a serious strain of a common bacterium — Staphylococcus aureus — and its effects in horses and humans.

S. aureus is often present in the nasal passages of healthy individuals and can cause secondary infections in both humans and horses. Although most S. aureus strains are of minimal concern, methicillin-resistant strains (MRSA) are a significant worry in human medicine. Physicians first discovered MRSA in humans in the early 1960s, just after methicillin, a drug that’s used as a substitute for penicillin, was introduced to treat staphylococci infections such as S. aureus.

The main problem with MRSA infections is that they’re difficult to treat because they’re resistant to most antibiotics. In humans, MRSA infection increases the chances of serious illness and death. It prolongs hospital stays and greatly increases treatment costs. Outbreaks of the infection can occur in a hospital, with the bacterium transmitted between patients directly or via the staff.

In horses, MRSA infections have been identified in a number of countries, including Canada, the United States and Japan. Transmission of the bacterium is thought to occur from direct contact between infected animals and people, but only a small percentage of them get sick. Many are MRSA carriers — those who test positive but do not show symptoms — and they have the potential to infect others with weaker immune systems.

The Ontario Veterinary College’s Veterinary Teaching Hospital has what is thought to be the most aggressive equine MRSA surveillance program in the world. Information gathered through ongoing surveillance has provided valuable information and has raised a number of important questions.

“This organism is one of a relatively small number of bacteria that can be transmitted from humans to horses and from horses to humans and can cause disease in both species,” says Weese. “With an emerging pathogen, there’s a tremendous amount of information we must uncover. It’s important to understand how it moves between different species, what problems it may cause and how to prevent and treat infections.”

Collecting data is easy, he says. All it takes is a simple nasal swab during a veterinary exami-nation or a blood, urine or skin sample taken by a human physician. Those samples are then cultured and analysed to determine if MRSA is present. The data collected are used to determine the number of individuals that are infected with or are carriers of MRSA.

“Through this research, we hope to determine the scope of MRSA infection in horses and people who work with horses,” says Weese. “We want people to understand the risks associated with MRSA infection both for other horses and for people and to find an alternative way for equine practitioners to treat MRSA carriers.”

This research is sponsored by the Ontario Veterinary College and Mount Sinai Hospital.

- Marianne Fallis, SPARK