MRSA Found in Danish Horses – University of Copenhagen

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20 April 2017

MRSA Found in Danish Horses


A new study shows that around 4% of all healthy Danish horses carry the so-called MRSA bacterium in their nasal cavity. 401 horses were examined as part of a research collaboration between the University of Copenhagen and Statens Serum Institut. The researchers behind the study were surprised to find such a high prevalence of MRSA, as the bacterium previously has not been found in healthy Danish horses.

MRSA is a staphylococcus bacterium found in both humans and animals. Compared to regular staphylococcus bacteria MRSA is more resistant to treatment with antibiotics. When it causes infection, killing the bacterium can therefore require stronger antibiotics. Around 9 out of 10 Danish pigs carry MRSA, but we have limited knowledge of the prevalence of MRSA in other animal species, including horses.

The latest research from 2005 showed that none of the 100 tested horses in Denmark carried MRSA. Now a team of researchers from the University of Copenhagen and Statens Serum Institut has shown that the prevalence of MRSA in horses has increased. They have examined 401 horses from stud farms, riding schools and private stables, and 17 of the tested horses carried MRSA in their nasal cavity.

‘The prevalence is surprisingly high compared to the previous study, and this development is confirmed by figures from other European countries, which also see an increase in the prevalence of MRSA in horses’, says Associate Professor Peter Damborg from the Department of Veterinary and Animal Sciences at the Faculty of Health and Medical Science, University of Copenhagen.

MRSA Can Be Transferred from Horses to Humans
None of the 17 MRSA-positive horses were sick due to the bacterium. But just as in humans MRSA and other staphylococcus can cause infection in horses, for example in animals with a weak immune system or in connection with wounds. As part of the study the researchers conducted DNA analyses of the bacteria and compared them to MRSA isolated over time from humans in Denmark.

‘The most frequent form of MRSA in horses was a special form of livestock MRSA. This form has been ascribed to horses, as it so far has not been found in other animals. However, in the period 2004-2015 the bacterium was found in three horse veterinarians, so it can be transferred to humans’, says Peter Damborg.

More Knowledge Is Required
In addition to the dominant horse-specific form, another two types of MRSA were identified, including livestock MRSA, which is the one most frequently found in Danish pigs. The MRSA-positive horses have not been in contact with pigs, though, so it is unclear where the bacterium has come from. According to Peter Damborg, there may have been a form of indirect contact with pigs, for example via humans. Alternatively, horses may represent a new, smaller reservoir of livestock MRSA.

’All in all, we can conclude that horses can be added to the list of possible sources of MRSA. Even though there is evidence to suggest that the bacterium is rarely transferred from horses to humans, we cannot know for sure how often it occurs. In order to answer these questions, we will need to follow up on our study’, says Peter Damborg.

He adds that he personally is not afraid of being around horses, as MRSA after all is no more dangerous than the other staphylococcus humans carry naturally.

The study ‘Horses in Denmark Are a Reservoir of Diverse Clones of Methicillin-Resistant and – Susceptible Staphylococcus aureus’ has just been published in the scientific journal Frontiers  in Microbiology.