MRSA in pigs in Holland – is there cause for concern?

A high level of MRSA (methicillin-resistant Staphylococcus aureus) has been isolated in 39% of pigs in Holland and also in pig farmers and vets and this is causing much consternation.

It is not so much for the pigs, where S. aureus is not associated with a specific disease problem, unlike Streptococcus suis for example, which still remains penicillin sensitive, but for the humans associated with pigs and other farm animals that might carry the infection into hospitals, where the major problems lie.

Ineffective
Methicillin resistance means that higher penicillins and cephalosporins, which are very commonly used in human medicine, are all ineffective.

This situation is interesting; why has it occurred in Holland, and to such an extent?

The presence of the organism has been reported in many other countries, such as Denmark, Germany, Austria and France but at a relatively low percentage. In the UK, they have not found it in pigs to date but they have not been actively screening for it.

However, several hundred milk samples from dairy cows, where methicillin-related compounds are used for the treatment of mastitis, have tested negative.

Antimicrobial use
So what has changed? The organic lobby is blaming antimicrobial use as usual, but we have been using antimicrobials for a long time, without inducing such a problem before.

There has to be a selector for the resistance mutation and this is reportedly a rare genetic occurrence. Has there been a major change in antimicrobial use in Holland to products that would select for resistance, i.e. the more advanced penicillins or cephalosporins?

Survey in Belgium
This has not been reported as the case. In one survey in Belgium it was reported that 5% of herds had started to use cephalosporins in piglets by injection as prophylaxis, probably against S. suis or Haemophilus parasuis. This would not affect 39% of the national herd.

There is an epidemiological study in progress in Holland but, to infect such a large number of pigs and farms so quickly (since 2004), suggests that it may have come down a large breeding pyramid, like PRRS did in the UK.

Major concern
This would be a major concern if this was the case and the breedingpyramid was exporting stock to other countries.

Meat, reportedly, does not carry a significant risk of transmission, but live breeding animals could.

Whilst we are in a situation where we do not know all the facts, as a precaution, it would be worth insisting that breeding animals from Holland be tested for MRSA before shipping to other countries, to prevent the same thing happening there.