It’s clear that methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a problem in dogs, both in terms of dog health and in terms of dogs as a potential sources of infection for people. It is thought that MRSA in pets is often (if not usually) acquired from people. Until recently, it has been unclear what makes individual dogs more likely to infected by MRSA compared to other bacteria. A study by Dr. Meredith Faires from the University of Guelph has provided some important new information in this regard. The study compared dogs with MRSA infections to dogs with infections caused by methicillin-susceptible strains of S. aureus (also called MSSA), from three large veterinary hospitals. Here are some key findings from Dr. Faires study:

• Animals that received fluoroquinolones were significantly more likely to develop an MRSA versus an MSSA infection.  Fluoroquinolones are a specific class of antibiotics that includes drugs such as enrofloxacin, orbifloxacin and marbofloxacin.
• In both groups (MRSA and MSSA), most of the infections were skin and ear infections, with no significant difference in types of infection between the groups.
• There was no difference in the proportion of animals that survived their infections between the two groups: in both groups, over 90% of the animals survived. However, it is important to bear in mind that the majority of the infections were skin and ear infections, which are not usually life-threatening.  Further study of more serious types of infection is needed to determine if MRSA is associated with a greater risk of death in dogs and cats.

This study provided more evidence that MRSA is an important problem in dogs and cats, and that the use of antibiotics is likely an important factor in the development of MRSA infections, compared to infections caused by MSSA. It also showed that the survival rate for common types of MRSA infections is high, if the infection is properly diagnosed and managed.  Hopefully the information provided by this study can be used in future studies to help evaluate more risk factors, and to identify things that can be done to reduce the impact of MRSA in dogs and cats.

More information about MRSA in pets can be found on the new MRSA information sheets posted on the Worms & Germs Resources page.

Picture: Gram stain of Staphylococcus aureus