Risk Factors for Contacts between Wild Boar and Outdoor Pigs in Switzerland: Investigations on Potential Brucella suis Spill-over

Based on a questionnaire, around one in four outdoor pig farmers reported contact between wild boar and domestic pigs. The country is officially free of brucellosis in domestic pigs. One farm was found to be positive although the source of infection was not identified.
calendar icon 7 August 2012
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Due to the parallel increase of the number of free-ranging wild boar and domestic pigs reared outdoor, the risk that they interact has become higher, according to a paper published recently in BMC Veterinary Research.

Along with co-authors from Service de la Consommation et des Affaires vétérinaires and Suisselab, Natacha Wu of the University of Bern in Switzerland explained that contacts with wild boar can be the origin of disease outbreaks in pigs, as it has been documented for brucellosis in some European countries.

Their study aimed at quantifying the occurrence of contacts between wild boar and outdoor domestic pigs in Switzerland, and identifying risk factors for these contacts. Furthermore, exposed pigs were tested for pathogen spill-over, taking Brucella suis as an example because B. suis is widespread in Swiss wild boar while domestic pigs are officially free of brucellosis.

Thirty-one per cent of the game-wardens and 25 per cent of the pig owners participating to a country-wide questionnaire survey reported contacts, including approaches of wild boar outside the fence, intrusions and mating.

Seventeen piggeries (five per cent) reported the birth of cross-bred animals.

Risk factors for contacts identified by a uni- and multivariable logistic regression approach were: distance between pig enclosure and buildings, proximity of a forest, electric fences and fences <60cm. Pigs of the Mangalitza breed were most at risk for mating with wild boar (births of cross-bred animals).

Blood and tissues of 218 outdoor pigs from 13 piggeries were tested for an infection with B. suis, using rose bengal test, complement fixation test and an IS711-based real-time PCR. One piggery with previous wild boar contacts was found infected with B. suis, however, epidemiological investigations failed to identify the direct source of infection.

Results show that interactions between wild boar and outdoor pigs are not uncommon, pointing at the existing risk of pathogen spill-over, concluded Wu and co-authors. Provided data on risk factors for these interactions could help the risk-based implementation of protection measures for piggeries. The documentation of a brucellosis outbreak in pigs despite the freedom-of-disease status underlines the importance of improving pathogen surveillance strategies and increasing disease awareness of farmers and veterinary practitioners.


Wu N., C. Abril, A. Thomann, E. Grosclaude, M.G. Doherr, P. Boujon and M-P. Ryser-Degiorgis. 2012. Risk factors for contacts between wild boar and outdoor pigs in Switzerland and investigations on potential Brucella suis spill-over. BMC Veterinary Research, 8:116. doi:10.1186/1746-6148-8-116

Further Reading

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

Further Reading

Find out more information on brucellosis in pigs by clicking here.

August 2012
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