Since the detection of MRSA CC398 in pigs in 2004, it has emerged in livestock worldwide, according to Els M. Broens of Wageningen University in the Netherlands and co-authors there and at the Dutch National Institute for Public Health and the Environment, the University of Copenhagen in Denmark, Animal Health Service in the Netherlands and the Operational Directorate of Bacterial Diseases, Veterinary and Agrochemical Research Centre and Ghent University, both in Belgium. In a paper to be published in BMC Veterinary Research, they continue that 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.

Sows and their offspring were sampled at varying intervals during a production cycle. Overall, MRSA prevalence of sows increased from 33 per cent before farrowing to 77 per cent before weaning. Overall MRSA prevalence of piglets was more than 60 per cent during the entire study period.

The recurrent finding of MRSA in the majority of individuals indicates true colonisation 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 tetracyclines and beta-lactams than untreated pigs, implying a selective advantage of MRSA CC398 when these antimicrobials are used.

Furthermore, transmission rates were higher in pre-weaning pigs than 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 than between-pen transmission and transmission through environmental exposure.

Broens and co-authors concluded that, from their results, it appears 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.

Reference

Broens E.M, C. Espinosa-Gongora, E.A.M. Graat, N. Vendrig, P.J. Van Der Wolf, L. Guardabassi, P. Butaye, J.P. Nielsen, M.C.M. De Jong and A.W. Van De Giessen. 2012. Longitudinal study on transmission of MRSA CC398 within pig herds. BMC Veterinary Research, 8:58. doi:10.1186/1746-6148-8-58

Further Reading

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You can view the full report (as a provisional PDF) by clicking here.