Germ-Free Dogs Still Potential Disease Carriers, Study Finds

May 08, 2009 - News Release

Therapy dogs visiting hospitals and nursing homes may be able to transmit diseases to people even if the animals themselves are germ-free, according to a new study by researchers at the University of Guelph's Ontario Veterinary College.

Prof. Scott Weese of the Department of Pathobiology and veterinarian Sandra Lefebvre, an OVC PhD graduate, found that dogs can pick up Clostridium difficile and methicillin-resistant Staphylococcus aureus (MRSA) bacteria while visiting hospitals and nursing homes, which could then pose a risk to the next person who pets or interacts with the animal. (Read the article about this research in the New York Times)

"This means that screening the animal for disease prior to entering a hospital or nursing home is not enough to prevent the transmission of disease," said Weese.

For the study, which was published recently in the Journal of Hospital Infection, the researchers tested 26 pet therapy dogs and their handlers before and after they visited hospitals and long-term-care facilities. All were found to be free of C. difficile and MRSA before the visits. But afterwards, C. difficile was discovered on the paws of one dog that had been "shaking hands" with patients. In addition, MRSA was discovered on the hands of an investigator who petted a dog after it had visited a long-term-care facility.

"This finding is important because it demonstrates that contamination of a dog's paws or fur can occur during visitation and, more important, that contamination can be transferred to people during normal petting," Weese said. "Once it's on someone’s hands, it can be transferred to anywhere on the body and potentially cause an infection."

The study emphasizes the need for people to practise good personal hand hygiene before and after touching pet therapy animals to prevent disease. It also underscores the importance of following the new guidelines for animal-assisted interventions in health-care facilities, he said.

The guidelines were developed in 2008 after U of G hosted a meeting of animal and human health experts from Canada and the United States on the topic. They stress personal hand hygiene and outline restrictions for therapy animals, such as health screening, limiting them to domestic household pets and testing for temperament.

This is the latest study Weese and Lefebvre, now with the Journal of the American Veterinary Medical Association, have conducted on therapy dogs and zoonotic diseases (those that can jump between animals and humans). In 2006, they found that 80 per cent of therapy dogs carry bacteria such as C. difficile MRSA, Salmonella, multi-drug-resistant E. coli and Giardia spp. In another 2006 study, Weese determined that MRSA can be freely passed between humans and household pets and that pets can act as silent carriers of the bacterium for several months.

Although the researchers have found various potential concerns regarding animal visitation programs, they stress that these programs can be beneficial and that attention to basic infection control practices can minimize risks.

"At the end of the day, if people wash their hands before and after petting the animal, the risks of disease transmission in a hospital are likely minimal," Weese said.

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 Barry Gunn, Ext. 56982/

University of Guelph
50 Stone Road East
Guelph, Ontario, N1G 2W1