Guelph Researchers Find MRSA in Pigs

November 08, 2007 - News Release

Pigs can now be added to the list of potential carriers of the drug-resistant "superbug" methicillin-resistant Staphylococcus aureus (MRSA).

Researchers at the University of Guelph have discovered the bacterium in 25 per cent of pigs and 20 per cent of hog farmers in Ontario. Their study — the first in North America — was published this week in the journal Veterinary Microbiology.

It's an important finding because it shows the bacterium can be readily passed from animals to humans even when contact between the two is more limited, said Prof. Scott Weese, a pathobiologist at Guelph's Ontario Veterinary College. He conducted the study with Profs. Cate Dewey and Robert Friendship and graduate student Taruna Khanna of OVC's Department of Population Medicine.

Previously, Weese and others have found MRSA in domesticated animals such as dogs, cats and horses, and determined it could be transmitted from animals to humans and vice versa. But human-animal contact tends to be different in those species than it is with pigs.

MRSA is a version of a common bacterium carried on the skin and in the nose that can cause skin, soft-tissue and other infections. Occasionally, "staph" –– as it is commonly referred to –– can get into the body and in rare cases cause an infection such as pneumonia in both humans and other animals.

MRSA is resistant to many common antibiotics, which can make treatment more difficult. In most cases, MRSA causes no or very minor symptoms, but in rare cases, it can lead to death, even in otherwise healthy people.

The researchers sampled 285 pigs on 20 hog farms in Ontario and found two main strains of MRSA present. One strain had previously been found in pigs in Europe and has emerged as an important cause of disease in people in some European countries. The other is the most common MRSA strain found in people in Canada.

The results raise concerns that the strain that is causing infections in people in Europe could result in similar problems in North America, Weese said. In addition, finding a common human MRSA strain in Ontario pigs indicates that people were likely the original source of the infection, he said.

Although MRSA doesn't typically cause illness in pigs as it does in people, "pigs could perhaps send this back into the human population," he said.

The researchers found no difference in the prevalence of MRSA among suckling, weanling and grower-finisher pigs, but they concluded that people working on pig farms are at higher risk for MRSA than the general population.
"The presence of MRSA in pig farmers was quite high — 20 per cent — compared with the general population in North America, which has a colonization rate of one to two per cent," Weese said.

The reason for this is unclear, he added. "Further research is necessary to identify and implement control measures to reduce the impact of this pathogen."

Because pigs are food-producing animals, the findings could raise concerns about food contamination, said Weese. "But the food-borne risks are probably minimal. The greater concern is the potential for pigs to serve as a source of MRSA infection for people in contact with the animals."

Prof. Scott Weese
Department of Pathobiology
519-824-4120, Ext. 54064

For media questions, contact Communications and Public Affairs: Lori Bona Hunt, 519-824-4120, Ext. 53338, or Deirdre Healey, 519-824-4120, Ext. 56982.

University of Guelph
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Guelph, Ontario, N1G 2W1