Friday, 18 May 2012

MRSA st398 (cc398) in pig herds - endemic


The Netherlands and Denmark provide more and more confirmation of the relevance and persistence of MRSA st398 (cc398) in pig herds.

But still a news back-out in Britain, apart from long outdated claim, following a perfunctory examination of a few dust samples forced upon Britain by the EU, that no MRSA has been found in British pigs. 

Abstract here

Longitudinal study on transmission of MRSA CC398 within pig herds

Els M BroensCarmen Espinosa-GongoraElisabeth AM GraatNadia VendrigPeter J Van Der WolfLuca GuardabassiPatrick ButayeJens P NielsenMart CM De Jong and Arjen W Van De Giessen
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BMC Veterinary Research 2012, 8:58 doi:10.1186/1746-6148-8-58
Published: 18 May 2012

Abstract (provisional)

Background

Since the detection of MRSA CC398 in pigs in 2004, it has emerged in livestock worldwide. MRSA CC398 has been found in people in contact with livestock and thus has become a public health issue. Data from a large-scale longitudinal study in two Danish and four Dutch pig herds were used to quantify MRSA CC398 transmission rates within pig herds and to identify factors affecting transmission between pigs.

Results

Sows and their offspring were sampled at varying intervals during a production cycle. Overall MRSA prevalence of sows increased from 33% before farrowing to 77% before weaning. Overall MRSA prevalence of piglets was > 60% during the entire study period. The recurrent finding of MRSA in the majority of individuals indicates true colonization or might be the result of contamination. Transmission rates were estimated using a Susceptible-Infectious-Susceptible (SIS-)model, which resulted in values of the reproduction ratio (R0) varying from 0.24 to 8.08. Transmission rates were higher in pigs treated with tetracyclins and beta-lactams compared to untreated pigs implying a selective advantage of MRSA CC398 when these antimicrobials are used. Furthermore, transmission rates were higher in pre-weaning pigs compared to post-weaning pigs which might be explained by an age-related susceptibility or the presence of the sow as a primary source of MRSA CC398. Finally, transmission rates increased with the relative increase of the infection pressure within the pen compared to the total infection pressure, implying that within-pen transmission is a more important route compared to between-pen transmission and transmission through environmental exposure.

Conclusions

Our results indicate that MRSA CC398 is able to spread and persist in pig herds, resulting in an endemic situation. Transmission rates are affected by the use of selective antimicrobials and by the age of pigs.