Abstract
BackgroundDue 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. Contacts with wild boar can be the origin of disease outbreaks in pigs, as it has been documented for brucellosis in some European countries. This 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.ResultsThirty-one percent of the game-wardens and 25% 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 (5%) reported the birth of cross-bred animals. Risk factors for contacts identified by a uni- and multivariable logistic regression approach were: distance between pigs enclosure and houses, proximity of a forest, electric fences, and fences ≤ 60 cm. 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 Brucella 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.ConclusionsResults show that interactions between wild boar and outdoor pigs are not uncommon, pointing at the existing risk of pathogen spill-over. 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.
Highlights
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
We report field investigations performed in the frame of a brucellosis outbreak in domestic pigs with a history of contacts with wild boar
Contacts between wild boar and pigs Questionnaire surveys among game-wardens and pig farmers Thirty-one percent (26/82) of the game-wardens who participated to the study observed contacts at least once between 1995 and 2008, and before 1995 for four of them
Summary
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. Rearing domestic pigs outdoor shows an increasing trend [4] This type of animal husbandry provides a better quality of life for pigs [5,6], it exposes them to a higher risk of contact with wild boar, which can carry pathogens with various routes of transmission [7]. Classical swine fever (CSF) virus and Mycobacterium bovis (causing tuberculosis) are transmitted by indirect or direct close contact [2,10] These pathogens are currently not an issue in Switzerland [11,12] but they could be introduced by wild boar emigrating from neighbouring countries [13,14,15]. While AD virus infection is rare in Swiss wild boar [11], nearly 30% of them are carrier of B. suis, including adults with genital organ infection [1]
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