By Dr. Becker
A new study led by researchers from the University of Cambridge in the U.K. suggests that in addition to humans, dogs and cats can also harbor the MRSA superbug. MRSA, or methicillin-resistant Staphylococcus aureus, is a bacterial infection that is highly resistant to antibiotics.
The study found that cats and dogs can carry the same genetic strain of MRSA that people do, which suggests the bacteria is transmitted from humans to their pets. However, while pets may harbor MRSA bacteria on their fur, they rarely develop an active infection.
MRSA Bacteria Easily Adapts When Transmitted from Humans to Pets
In the laboratory study, which was published in the May 2014 issue of the journal mBio,1 MRSA samples from cats and dogs were compared to human samples. From 2003 to 2007, the researchers mapped the DNA sequences of 46 MRSA samples from cats and dogs in the U.K. Most of the samples were from wound, skin, and soft tissue infections, with the remainder coming from urine, cerebrospinal fluid, nasal secretions, the bloodstream, and heart valve and joint infections.
The researchers then compared the pet samples to a collection of previously sequenced human MRSA samples, and also analyzed the evolution of different bacteria.
What they found was that most of the dog and cat infections were from the same MRSA family, a common strain in the U.K. and Europe called Epidemic MRSA 15. Almost all the samples were genetically similar to human bacteria, suggesting that the bacteria the pets harbored were likely to have been transmitted by humans.
DNA analysis showed very few genetic changes between bacteria samples from humans and animals, indicating the cat and dog MRSA bacteria did not require much adaptation to survive on different types of animals or humans.
Interestingly, the researchers also discovered that the animal MRSA was much less likely than the human MRSA to be resistant to the antibiotic erythromycin – a drug very rarely used in U.K. veterinary practices. However, the pet MRSA was more likely to be resistant to the antibiotic clindamycin, which is widely used by veterinarians in the U.K. In other words, the dog and cat MRSA bacteria was responsive to an antibiotic not overused in pets in the U.K., but was resistant to an antibiotic that is likely overused.
MRSA Bacteria Can Be Passed Back and Forth Between People and Their Pets
From their study results, the University of Cambridge research team determined that:
- Humans and pets share the same strain of MRSA, indicating the bacteria can be passed back and forth without needing to adapt.
- Companion animals may act as a reservoir for human MRSA infections and vice versa.
- It appears MRSA can be easily transmitted in veterinary clinics as well as human hospitals.
According to Mark Holmes, senior author of the study:
“Our study demonstrates that humans and companion animals readily exchange and share MRSA bacteria from the same population.
“It also furthers the ‘one health’ view of infectious diseases that the pathogens infecting both humans and animals are intrinsically linked, and provides evidence that antibiotic usage in animal medicine is shaping the population of a major human pathogen.”
Study Results ‘May Influence Future Antibiotic Prescribing Patterns’
MRSA, of course, is a major problem in the human population. Since the late 1990s, scientists have been researching the role of livestock and companion animals in harboring and transmitting MRSA. As an example, it is estimated that up to 9 percent of U.K. dogs are carriers of MRSA.
While these study results are important, we need to remember that MRSA infections in pets are rare. More important are good hygiene practices when handling and caring for pets.
PubMed Health suggests that, “The results [of the study] may influence future antibiotic prescribing patterns in animals as well encouraging a holistic approach towards treating infections; where we consider both the needs of humans and animals.”2