A common question from owners of pets infected with methicillin-resistant Staphylococcus aureus (MRSA) is "Where did it come from?" The answer is not completely clear, but evidence strongly suggests it probably came from humans. The MRSA strains found in pets are almost always teh same as those found in people (including people that don’t have pets) in the same geographic area. This strongly suggests that the MRSA came from the same source. Considering the fact that S. aureus in general is much more common in humans than in pets, and how long MRSA has been around in people, and that MRSA can sometimes be found in both people and pets in the same household, it is very likely that MRSA can move between species and originally went from humans to animal.

Even though MRSA in pets probably originated from people, now that it is in the pet population, pets can spread it to other animals and back to people. It is unclear how frequently this occurs – most people are still more likely to encounter MRSA from another person than from an animal.

The emergence and spread of MRSA in humans was largely driven by extensive antibiotic use in people.  Once MRSA crossed over to pets, antibiotic use in these animals almost certainly played a role in helping MRSA spread in the pet population. Antibiotic treatment has been identified as a risk factor for development of MRSA infection in dogs, and for MRSA carriage in horses.

Prudent antibiotic use is likely the most important factor in reducing the risk of MRSA in individual pets.  Using antibiotics prudently means doing things like:

  • Only using antibiotics when they’re really necessary
  • Using the most basic antibiotic possible (instead of the fanciest or most powerful antibiotic)
  • Finishing every prescription completely and as directed)