Equine Science Update

Horse veterinarians are more likely to carry methicillin-resistant Staphylococcus aureus (MRSA) with them than are their colleagues who are involved in other types of work, according to an Australian study.

Staphylococcus aureus is a bacterium that can cause disease in both animals and humans. Normal healthy people may carry the organism in their nostrils. It may also be present in other areas such as the throat and skin and will quickly colonise damaged or abnormal skin. It is commonly involved in infected wounds, and may cause joint infections.

Usually, Staphylococcus aureus infections can be treated effectively with antibiotics. However, there is a growing problem of resistance to antibiotics. Strains of Staph. aureus resistant to methicillin were first identified in the 1960s. Since then, the problem has become worse. Now, MRSA is often resistant to a

wide range of antibiotics including the aminoglycosides (eg, gentamicin), tetracycline, and erythromycin. MRSA has rapidly developed resistance to the fluoroquinolones, a relatively new class of antibiotic.

MRSA is no more infectious than "normal" methicillin-sensitive Staphylococcus aureus. But because it is resistant to a wide range of antibiotics it is more difficult to treat.Some strains of MRSA cause rapid and extensive tissue necrosis in humans often attributed to the possession of virulence factors such as toxins.

Methicillin-resistant Staphylococcus aureus is now a major clinical problem in human hospitals. It is becoming increasingly important in equine medicine.

Normal healthy individuals may carry MRSA without showing signs of disease. Problems arise when the bacteria contaminate wounds, particularly in individuals whose natural immunity is depressed.

Findings of research into the prevalence of the organism in Australian vets were presented at the annual conference of the Australian Veterinary Association in Adelaide, May 2011. The work has been published in the Australian Veterinary Journal.

The researchers, led by Dr David Jordan, collected nasal swabs from 771 individuals, who were also asked for details of the type of work they did and with which species.

Analysis of the data showed that veterinarians that worked mainly or exclusively with horses were more likely the carry MRSA in their nostrils.

MRSA could be isolated on nasal swabs from 5.8% of those taking part in the study. However, the data revealed differences depending on the type of work the individuals performed.

Positive swabs were obtained from 11.9% of veterinarians who spent a lot of their time on horse work. (This was 13 times that of the vets involved in industry or government work. Less than 1% of them had positive swabs).

The figures were even higher among people who worked only with horses.  The results showed that 21.35% of them had nasal swabs positive for MRSA. (They were 23 times more likely to have their nostrils colonised by MRSA than were vets working for government or industry.)

Considering the extent of carriage of MRSA and the seriousness of the disease it can cause in humans and animals, Dr Jordan recommended that vets should take more precautions to prevent the spread of MRSA

"The higher than normal prevalence of MRSA carriage among veterinary clinicians in Australia is a cause for concern in the profession and warrants further investigation for specific risk factors, particularly for vets who work with horses"

He suggests that guidelines specific for equine work are needed. These should include: "enhanced personal hygiene during handling of animals; better sanitary management of premises, equipment and waste; greater awareness of biosecurity during handling and surgical procedures; and reform of use of antibiotics - especially those of importance in human medicine such as the fluoroquinolones, third generation cephalosporins and gentamicin."




For more details see: Carriage of methicillin-resistant Staphylococcus aureus by veterinarians in Australia
D Jordan, J Simon, S Fury, S Moss, P Giffard, M Maiwald, P Southwell, MD Barton, JE Axon, SG Morris, DJ Trott,
Australian Veterinary Journal (2011) 89, 152-159