Pet Talk: The facts about MRSA
By Melissa Giese/University of Illinois College of Veterinary Medicine
According to the Centers for Disease Control and Prevention, MRSA is one of the most common causes of human skin and soft tissue infections, and it is the 10th-leading cause of death in humans in the United States.
MRSA stands for “methicillin-resistant Staphylococcus aureus.” Staphylococcus bacteria are found on the skin of healthy individuals and, under normal conditions, do not cause a problem. However, when introduced via a break in the skin, these bacteria can become dangerous to people and pets.
“MRSA bacteria have an enzyme called penicillin binding protein II that interferes with many drugs used to treat bacterial infections, including penicillins, methicillin, oxacillin and cephalosporins,” said Dr. Carol Maddox, a professor at the University of Illinois Veterinary Diagnostic Laboratory in Urbana.
People often wonder if their pets may be susceptible to or a source of this drug-resistant bacteria.
“There is a low incidence of MRSA in pets compared with humans,” Maddox said. “Cats and dogs are more often carriers or infected with a different staphylococcus, Staphylococcus pseudintermedius, which is very seldom infectious to humans.”
MRSA can be found in many unexpected places. It is spread by direct physical contact with a colonized or infected person or contaminated object. Hospitals provide an environment conducive to the transmission of these bacteria between patients. “The first MRSA outbreak occurred in the late 1960s, and MRSA had spread worldwide by the early 1980s,” Maddox explained. “Since the 1990s we have been seeing more community-acquired, rather than hospital-acquired, MRSA, and the infection is increasingly found in companion animals.”
The resistant bacteria arise when something threatens their survival, such as an antibiotic or some disinfectants, which results in selection of bacteria with traits enabling them to survive. If the antibiotic does not kill all the bacteria present, the surviving bacteria will carry the resistant trait and may pass the trait on in the form of plasmid DNA, enabling a new strain of resistant bacteria to emerge.
“This newly emerged resistance can also be transferred by bacteriophages, viruses that can infect bacteria,” Maddox said. A bacteriophage has a chance of picking up the resistance genes and transferring them to another bacteria. This process may lead to super bacteria that are much tougher to kill.
Skin problems are the most common manifestation of a MRSA infection. In dogs superficial pyoderma is a very common skin infection, while humans get a condition called exfoliative dermatitis in which the skin blisters.
“Staphylococci in general produce abscesses that can be found almost anywhere on the body. They cause tissue death and pus production at the infection site,” Maddox said. “In severe cases, toxic shock syndrome can occur due to the toxins created by the bacteria. The body’s inflammatory response overwhelms the patient and can lead to death.”
Although there is a possibility of transmission of MRSA between animals and humans, recent studies have shown that transmission is uncommon.
“Certain staphylococci and their toxins are host specific. This means that a toxin produced by one type of staphylococcus may cause a lot of problems for pets but little problems for humans or vice versa,” Maddox said.
Although unlikely, it is possible for MRSA to pass between people and pets. The American Veterinary Medical Association recommends that persons who have MRSA should get their pets tested, and owners of pets that have MRSA should get tested as well. The Centers for Disease Control and Prevention recommends preventing MRSA by maintaining good hygiene and keeping any wound clean and covered until healed. Wearing gloves and washing hands after treating infection sites are very important practices to prevent spread of these bacteria.