Elsevier

Veterinary Microbiology

Volume 141, Issues 1–2, 24 February 2010, Pages 96-102
Veterinary Microbiology

Methicillin-resistant Staphylococcus aureus in horses and horse personnel: An investigation of several outbreaks

https://doi.org/10.1016/j.vetmic.2009.08.009Get rights and content

Abstract

At the Veterinary Microbiological Diagnostic Center, the Netherlands, the percentage of methicillin-resistant Staphylococcus aureus (MRSA) isolates found in equine clinical samples increased from 0% in 2002 to 37% in 2008. MRSA of spa-type t064, belonging to MLST ST8 and spa-types t011 and t2123, both belonging to the livestock-associated MLST ST398, predominated.

During an outbreak of post-surgical MRSA infections in horses at a veterinary teaching hospital in 2006/2007, MRSA isolates of spa-type t2123 were cultured from 7 horses and 4/61 personnel which indicated zoonotic transmission. After intervention the outbreak stopped. However, another outbreak occurred in 2008, where 17 equine MRSA isolates of spa-type t011 (n = 12), t2123 (n = 4), and t064 (n = 1) were found. This time, 16/170 personnel were positive for MRSA with spa-type t011 (n = 11) and t2123 (n = 5). Personnel in close contact with horses were more often MRSA-positive (15/106) than those without (1/64).

Screening of horses upon admission showed that 9.3% were MRSA-positive predominantly with spa-type t011. Weekly cross-sectional sampling of all hospitalized horses for 5 weeks showed that 42% of the horses were MRSA-positive at least once, again predominantly with spa-type t011, which suggests that nosocomial transmission took place. Fifty-three percent of the environmental samples were MRSA-positive, including samples from students’ and staff members’ rooms, and all were spa-type t011. This indicates that humans contribute to spreading the organism. Culturing of samples employing high-salt pre-enrichment performed better than a comparable method without pre-enrichment.

Our results show that nosocomial transmission occurs in equine clinics and suggests that personnel play a role in the transmission.

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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