TDK conference 2019

Methicillin-resistant Staphylococcus aureus (MRSA) infections are currently a serious challenge in equine medicine. In 2016 an investigation of the clinical MRSA isolates at the University Equine Clinic (UEC) revealed permanent presence of the same clonal lineage ST398-t011-SCCmecIV with almost the same resistance pattern. This clonal lineage is highly specific to horses and can be found in most equine clinics across Europe. Based on the above, the strains are very likely to be of nosocomial origin. Despite the hygienic measures introduced in the UEC, MRSA and related clinical cases can be still a matter of concern. As horses can be healthy carriers of MRSA for longer periods of time, they represent a potential reservoir for strains causing recontamination of the clinical environment, or even introduce MRSA into the population outside the clinic.

To assess the possibility of MRSA (re-)contamination of the clinic, the horse cases at the UEC were first sampled upon arrival (hygienic screening). Second, horses on farms with recent history of an MRSA outbreak or with known MRSA positive status (targeted sampling) and randomly chosen farms with unknown MRSA status (random sampling) were also examined to evaluate the MRSA-burden of horses outside the clinic. All samples were tested for MRSA and the isolated strains were examined by phenotypic and molecular methods. In case of the targeted and random sampling, complementary data were also collected in the form of a questionnaire.

Between June 2019 and December 2019, only 8 MRSA strains were isolated from the 129 sampled horses (6.2%) during the hygienic screening. All but one isolate belonged to the ST398-t011-SCCmecIV genotype and most of them shared the same wide resistance pattern. The targeted sampling revealed an average of 4,5% (15/329) MRSA prevalence on 5 farms. The prevalence rate varied between 0-50% among the selected farms. Most of the strains had the aforementioned genotype and highly similar resistance profiles. Out of the five farms, only one had no recent history of equine clinic-related MRSA case at the time of the survey. Both in the hygienic and targeted sampling, only one other genotype was identified: ST1-t127-SCCmecIV. MRSA could not be isolated from the 325 samples taken from 24 farms in the random sampling, although from these horses at least 14 visited an equine clinic of known MRSA positive status in the same year.

The results show a low prevalence of MRSA in the Hungarian equine population in accordance with previous reports on the matter from Europe. This finding discourages the theory of wide-scale and long-term contamination of the population with strains of equine clinic origin. However recent sporadic cases with MRSA strains of high genetic and resistance homogeneity highlight the epidemiological role of farms and clinics where MRSA is endemic. At the same time, it emphasises the importance of local infection control measures on both the affected farms and clinics.