By: Andrea M. Bagley RN, BSN, CEN
Although rare, zoonotic diseases such as Methicillin –resistant Staphylococcus aureus (MRSA) have been shown to be transmitted from humans to horses and horses to humans putting those that work with horses at a higher risk. According to recent research, MRSA is up to ten times more common in equine veterinarians than the rest of us.
MRSA is well known to humans as being a resistant strain of the common S. aureus bacteria that inhabits our skin, respiratory tract, and wounds.
Similar to humans, horses can transmit the bacteria to each other by contact or through contaminated surfaces such as feed buckets, fences etc. Also similar to humans, horses can be carriers of the bacteria but not always be symptomatic of clinical disease. Horses may acquire the bacteria after being hospitalized or from horses at their home farm that have been hospitalized and were exposed while there.
Up to 5 % of the general population of equines has been shown to carry MRSA with about 10% of healthy horses being colonized in their noses.
A 2006-2006 study done at the University of Utrecht in the Netherlands showed that 43% of horses that went into the hospital clinic cultured positive for MRSA during their stay, over 9% of horses were positive carriers upon arrival to the clinic and 15% of the hospital employees were carriers.
Most of the MRSA infections in North American equines are caused by a human strain that is thought to have adapted to horses called MRSA-5 (CMRSA-5) or USA500 and it is commonly found on humans that work with horses. In Europe, the ST398 strain has been found in horses.
An example case from the CDC’s 2011 Emerging Infectious Disease Journal Volume 17, Number 6, is a 16 year old wheelchair bound girl from the Netherlands that had a right foot infection which cultured positive for ST398. She had extensive contact with a foal that also had a strain of MRSA with an identical susceptibility pattern.
An additional study from 2000-2002, of MRSA infected humans that worked with horses showed that one veterinarian had a tattoo site infection positive for the same subtype of CMRSA-5. This was the same strain that was isolated from two horses that had been in his care for a week before his wound became infected.
At the 2017 American Association of Equine Practitioners Convention, a Japanese study was presented that looked at horse and human swabs taken from veterinary hospitals and equine training centers. The outcome of this study showed that 16 of the 53 veterinarians tested were positive for MRSA and 10 of them had the same strain that was isolated in the 9 infected horses out of 600 they tested.
Diagnosis of MRSA in horses is done by bacterial culture and all strains of it are resistant to the beta-lactam family of antibiotics. However, most horses eliminate the colonization on their own within a few weeks unless re-exposed and don’t require treatment unless clinical disease is present.
To decrease the spread of disease, infected horses should be quarantined from others and proper hand hygiene cannot be overlooked.
Andrea Bagley is a registered nurse working in an emergency department in a small community hospital in Massachusetts. Andrea is a certified emergency nurse with a Bachelor of Science in Nursing and a Bachelor of Arts in Biology and is an avid equestrian riding and competing her horse in her spare time.
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