Methicillin-resistant Staphylococcus aureus infection

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium known to be resistant to most antibiotic medications and therefore if it infects an animal (or human) the infection can be difficult to impossible to treat and can pose a serious risk to life.

MRSA is any strain of the Staphylococcus aureus bacterium that has developed resistance to most available antibiotics, making infections from this bacterium extremely difficult to treat. As with most bacteria, it can be spread between animals and humans and it is commonly seen in human hospitals. It is vital that any animals or humans suspected of carrying MRSA are carefully monitored to prevent cross contamination.

Animals are normally infected by human carriers, or in veterinary environments where the bacteria can multiply and invade open wounds, surgical wounds, intravenous catheter sites or any other invasive device site (such as chest drains). Guinea pigs with a weakened immune system, and the very young or old, are at a greater risk of contracting a nosocomial infection (hospital-acquired infection).

The most commonly encountered clinical sign with MRSA is non-healing wounds or persistent infection despite treatment with antibiotics. Simple, sterile surgical wounds should heal and scar over within 7-14 days (larger wounds, and those in areas under movement or tension may take slightly longer). Wounds which fail to do this or keep opening up, are red and sore or that have odor or discharge may be infected with MRSA. Similarly, sites where intravenous catheters were placed may be red, hot and discharging fluid. Open wounds such as pododermatitis (sore hocks), flystrike wounds, or other wounds which may take several weeks or months to heal, may never heal and continually become infected.

An infected guinea pig is highly likely to feel unwell. They may show signs of anorexia or a reduced appetite, pass fewer droppings or stop altogether, grind their teeth in pain (bruxism), have a fever (pyrexia) and be lethargic. They will try and hide these signs for as long as possible.

MRSA can be diagnosed by taking a swab from the site of infection to send away for culture and sensitivity to ascertain the bacterium involved and what antibiotics are likely to be effective.

In humans, ‘super’ antibiotics are reserved for these hard-to-treat infections. These may not be available or suitable to use in guinea pigs due to factors such as cost, availability (some antibiotics are only used in humans so overuse and resistance do not build up), or the fact that some antibiotics are unsuitable to use in guinea pigs due to the way they ‘destroy’ not only the bacteria they are intended to kill, but also the ‘friendly’ bacteria in the guinea pig’s digestive system. This can cause serious and fatal diarrhoea.

It may be a case that the infection cannot be cleared and supportive treatment by way of other antibiotics, analgesia, prokinetic medication and syringe feeding may be attempted to try and help the guinea pig to feel more comfortable. If the infection cannot be bought under control, then euthanasia may need to be considered if the guinea pig is suffering.

The key to prevention is two-fold. It is imperative that in human and veterinary medicine, antibiotics are used only when they are necessary and strictly following dosage and administration instructions. Failure to do this is leading to further resistance of the antibiotics that are currently available.

Within the veterinary practice all clinical staff must observe high hygiene standards. Hand washing between patients with antiseptics, wearing PPE and following strict infection control between patients is the most effective way to prevent the spread of MRSA in the veterinary environment.

Infection within the veterinary hospital environment is thought to be relatively rare.

The true numbers are unknown, but evidence shows that up to 30% of the human population are carriers and as mentioned earlier, they can spread this to animals. If you or one of your family members is a known carrier, it is important to disclose this to veterinary clinic staff so that precautions can be employed to protect your guinea pig and other patients in the veterinary clinic.

Although there is a risk, this is incredibly small, and it should not put you off taking your guinea pig to the veterinarian when they need treatment. Veterinary professionals are diligent with infection control, so the risks are not high.