I’ve had this question a lot lately. Methicillin-resistant Staphylococcus pseudintermedius (MRSP), which is sometimes misidentified as methicillin-resistant S. intermedius (MRSI), is an important and increasing cause of infections in dogs and cats. After an animal has had an MRSP/MRSI infection, a question people often ask is how long they will carry the bacterium?

MRSP can be carried in the nose, intestinal tract or on the skin of a small percentage of normal animals. The implications of this are not clear, but it is reasonable to assume that carriers are more likely to develop infections in certain situations (e.g. if they sustain a wound or need to have surgery), and can transmit it to other animals (and possibly people, but that’s much less of a concern with MRSP than with MRSA).

Back to the question… To be perfectly honest, we really don’t know. However, I think it’s reasonable to assume that some animals could carry MRSP for a long period of time – certainly weeks or months, maybe even years. Staphylococcu pseudintermedius is a common bacterium in healthy dogs and cats, and has basically evolved to survive on these animals. The methicillin-resistant versions are likely no different in this respect, so it’s reasonable to assume that some animals could be long-term carriers. This makes controlling MRSP more difficult.  In contrast, MRSA appears to be only transiently carried by dogs and cats, probably because it is better adapted to living on humans than pets.

What you should do in the meantime if your pet has MRSP:

  • Treat any infection as per your vet’s instructions.
  • Always complete the full treatment course.
  • Wash your hands after contact with your pet, healthy or not.

More information about different types of staph bacteria can be found in the previous Worms&Germs post entitled Methicillin-Resistant Staph – What’s In A Name?