MRSA - is it a problem in the kennels?

Trevor Turner, B. Vet. Med., MRCVS

WHAT IS STAPHYLOCOCCAL AUREUS?

Staphylococcal aureus is a bacterium that has been associated with skin infections both in people and in animals for many years. In people it is a very common cause of infected wounds, boils, pimples and pustules. In addition it is also often carried in the noses, throats and on the hands of perfectly healthy people.

Over fifty years ago when penicillin first came on the market it was forecast that Staph-generated boils and such like would soon become a thing of the past. Unfortunately, we reckoned without the resistance-developing abilities of the Staphylococcus. Resistance was soon developed to this new wonder drug. Staphylococcal organisms cause similar skin problems in our dogs and cats. For example, infected eczema, (pyoderma) is often due to Staphylococcal organisms. However, over time variations have occurred so that the Staphs. causing problems in our pets tend now to be a sub-type of Staph. aureus and are known as Staph. intermedius.

Staph. organisms, usually of intennedius type, can also be found in the noses, ears and skins of healthy animals.

Over the years, as it was realised that these staphylococcal organisms were capable of developing significant resistance to the ever more powerful antibiotics being developed to eradicate them, so the race was on to develop even more powerful antibiotics to combat this new breed of 'superbug.' However, provided the superbug did not cause any problems to its host, be it man or pet, there was little concern. The fact that you, I or our dogs carried staphylococcal organisms, be they Staph. aureus or Staph. intermedius, be they penicillin-sensitive or partially antibiotic-resistant, was of little interest provided they were causing no trouble.

Ampicillin, a synthetic penicillin, was developed in the late 1950s and by 1962 cases of Staph. aureus infection resistant to this “super drug” were recorded. However, such occurrences were extremely rare, but as we accrued more knowledge about canine skin diseases in particular it was realised that although Staph. intermedius was not the same as Staph. aureus, antibiotic resistance was developing in dogs and cats, very similar to that being experienced in the human field.

Ever more resistant Staphs. were appearing. As a result calls were made to the veterinary profession to reduce the indiscriminate use of antibiotics, not particularly with synthetic penicillins and Staph. aureus in mind. This advice was directed at the medical profession in general, it suddenly becoming realised that antibiotics were not the panacea for all ills and there was a very serious risk of the development of antibiotic resistance by a wide variety of pathogenic (disease producing) bacteria, among which were - you've guessed it - the Staphylococcal species, aureus and intermedius. In the 1970s methacillin-resistant Staphylococcal aureus (MRSA) accounted for about 2% of hospital-acquired infections worldwide. That figure rose to 43% in 2002.

However not all these infections were serious or life threatening. They merely represent the detection of MRSA.

WHEN DO THESE ANTIBIOTIC-RESISTANT STAPHS. BECOME A PROBLEM?

When they stop being commensals and become pathogenic. In other words when they stop being harmless and start causing disease. This is usually quite rightly attributed to being "run down" or having an immune problem, which is exactly the situation with MRSA.

If the patient is immune-compromised for any reason, e.g. as a result of illness, disease, HIV etc, or even following a long general anaesthetic and operation, resistant Staphylococcal organisms can multiply and result first of all in local infections such as boils, pustules etc, followed by generalised infection as the body's weakened resistance is overcome. This can result in septicaemia (blood poisoning). Obviously as soon as any such complication arises, tests are carried out to establish the cause of the infection and the antibiotic sensitivity of the organism. It is only over the last few years that it has become realised that more and more very resistant Staphs. (all of which tend to be labelled methacillin resistant) have come to light.

CAN NOTHING BE DONE?

WHERE DO OUR DOGS ACQUIRE MRSA?

Recent work has shown that dogs (and cats) can acquire MRSA from owners who may or may not have shown any signs of having the infection. Dogs are also at risk if they are involved in hospital work, e.g. PAT Dogs. It also appears that dogs undergoing veterinary treatment, particularly following surgery, can acquire the infection from apparently healthy veterinary staff. After all it has been shown that anything from between 25 and 50% of the population do carry Staph. aureus although this does not mean they are all resistant strains.

The number of cases involving animals undergoing veterinary treatment diagnosed with MRSA is still, compared with humans, very small. Also at the time of writing I have not been able to find out exactly how many of these reported cases are actually MRSA or an equally resistant strain of Staph. intermedius.

Nevertheless MRSA does exist with our pets as I am sure does MRSI - methacillin resistant Staph. intermedius.

HOW GREAT, THEN IS THE RISK? CAN DOGS BE CARRIERS?

Is the problem truly zoonotic? Can it be passed from our pets to kennel staff?

Obviously if you work in kennels, are healthy and happen to pick up Staph. aureus from a boarder, it matters not one iota provided the Staph. aureus does not become pathogenic and turns out to be antibiotic resistant (MRSA). If you develop a Staph. infection, however, and tests show that it is insensitive to antibiotic treatment, the matter is serious. Therefore prevention is the name of the game.

HOW IS PREVENTION ACHIEVED?

The situation is really no different from that which applies to hospitals, be they veterinary or the human kind. Scrupulous cleanliness is the name of the game.

Because MRSA is, by definition, antibiotic resistant, this does not mean that it is disinfectant resistant. Good old soap and water and plenty of hand washing can go a long way to reducing this, as will safe disinfectants. Regular readers will know of my affection for domestic bleach. Diluted according to directions this is simple, cheap, and safe provided directions are followed. Bleach, however, is not that kind to work-worn hands and MRSA has certainly highlighted the need for continuous personal hygiene in addition to scrupulous cleanliness of the environment. In this way the number of Staphylococcal organisms, irrespective of whether methacillin resistant or not, is dramatically reduced. Hence the emphasis on higher standards of cleanliness in NHS hospitals.

The old adage, prevention is better than cure, has never been more apt but keeping the matter in perspective, remember that at present, the risk of MRSA for our dogs is very small. Recent work has shown that it is more likely to pass from a carrier person to a susceptible dog than the other way round, hence the need for perhaps more personal hygiene than in the past.