Methicillin-resistant Staphylococcus aureus in horses and horse personnel: An investigation of several outbreaks
Introduction
Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging equine pathogen. Initial reports of MRSA infections in horses largely concerned sporadic infections associated with veterinary hospitals (Hartmann et al., 1997, Seguin et al., 1999). However, the number of reports on MRSA colonization and infections in horses is increasing and they are now also associated with private practices and the community (Weese and van Duijkeren, 2009). The prevalence of MRSA colonization published so far varied between 0% and 4.7% on horse farms in Europe, Canada and North America (Busscher et al., 2006, Baptiste et al., 2005, Vengust et al., 2006, Weese et al., 2005), between 2.9% and 10.9% in horses admitted to equine clinics (Weese et al., 2006, Van den Eede et al., 2009) and 16% in horses in an equine hospital (Baptiste et al., 2005). In hospitalized horses, surgical site infections predominate, whereas joint, incision and skin/soft tissue infections are most common in community-onset infections (Weese and van Duijkeren, 2009). In Canada and North America most equine MRSA infections are caused by a human epidemic clone of Multilocus Sequence Type (MLST) ST8 (Canadian MRSA-5 or USA500) (Weese and van Duijkeren, 2009). It has been suggested that this MRSA is horse-adapted because of its predominance in horses and horse personnel (Weese and van Duijkeren, 2009). Recently, there have been reports on colonization and infection of horses with MRSA ST398 (Van den Eede et al., 2009, Witte et al., 2007), a MRSA clone associated with livestock (de Neeling et al., 2007, Graveland et al., 2008). The emergence of two clusters of MRSA infections at an equine veterinary teaching hospital in 2006/2007 and 2008, respectively, and the subsequent demand for outbreak management and MRSA control measures, prompted us to perform a study on colonization rates of horses and horse personnel, the possible occurrence of nosocomial transmission and the degree of contamination of the hospital's interior.
Section snippets
Horses
In December 2006 and early 2007, 7 horses originating from different provinces in the Netherlands developed MRSA infections shortly after colic surgery at the veterinary teaching hospital. Six patients had surgical wound infections and one had thrombophlebitis. All isolates were genotyped by Pulsed-Field Gel Electrophoresis (PFGE), spa-typing, SCCmec-typing and Multiple Locus Variable-number tandem repeat Analysis (MLVA) as described below. One isolate was typed by MLST.
Personnel
In February 2007, 61
Horses
The 7 clinical isolates from 2006 and 2007 were all non-typeable by PFGE, MLVA-type MT0568, SCCmec-type IVa and spa-type t2123 and were PVL-negative. The isolate analyzed by MLST was ST398.
Personnel
4/61 personnel were found positive, all with the same MRSA strain with MLVA-type MT0568 and spa-type t2123.
Horses
The clinical MRSA isolates (n = 12) in 2008 were spa-type t2123 (n = 2), t011 (n = 9) and t064 (n = 1), respectively. Seven isolates were analyzed by MLVA: the isolates of spa-type t2123 were both MLVA-type
Discussion
Earlier studies among equine clinical isolates in the Netherlands (van Duijkeren et al., 2004) and a survey among 200 healthy horses (Busscher et al., 2006) did not reveal MRSA. The reason for the sharp increase in the number of equine MRSA infections since 2006 is currently unknown. The high prevalence of ST398 in pigs and veal calves in the Netherlands (de Neeling et al., 2007, Graveland et al., 2008) and the fact that horses are often kept on farms with other livestock and are sometimes
Acknowledgement
This study was supported by a grant of the Dutch Ministry of Agriculture, Nature and Food Quality.
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