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Open Access Research article

Longitudinal study on transmission of MRSA CC398 within pig herds

Els M Broens12*, Carmen Espinosa-Gongora3, Elisabeth AM Graat1, Nadia Vendrig1, Peter J Van Der Wolf4, Luca Guardabassi3, Patrick Butaye56, Jens Peter Nielsen7, Mart CM De Jong1 and Arjen W Van De Giessen2

Author affiliations

1 Quantitative Veterinary Epidemiology Group, Wageningen Institute of Animal Sciences, Wageningen University, P.O. Box 338, Wageningen, 6700 AH, The Netherlands

2 Centre for Infectious Disease Control Netherlands, National Institute for Public Health and the Environment, P.O. Box 1, Bilthoven, 3720 BA, The Netherlands

3 Department of Veterinary Disease Biology, Faculty of Life Sciences, University of Copenhagen, Stigbøjlen 4, Frederiksberg C, 1870, Denmark

4 Pig Health Department, Animal Health Service, P.O. Box 9, Deventer, 7400 AA, The Netherlands

5 Operational Directorate of Bacterial Diseases, Veterinary and Agrochemical Research Centre, Groeselenberg 99, Bruxelles, 1180, Belgium

6 Department of Pathology, Bacteriology and Avian diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, Merelbeke, B-9820, Belgium

7 Department of Large Animal Sciences, Faculty of Life Sciences, University of Copenhagen, Stigbøjlen 4, Frederiksberg C, 1870, Denmark

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Citation and License

BMC Veterinary Research 2012, 8:58  doi:10.1186/1746-6148-8-58

Published: 18 May 2012

Abstract

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 β-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.

Conclusion

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.

Keywords:
Methicillin resistant; Staphylococcus aureus; Transmission; Pigs; MRSA; Reproduction ratio