Use of a Bayesian network model to identify factors associated with the presence of the tick Ornithodoros erraticus on pig farms in southern Portugal.

The soft tick Ornithodoros erraticus occurs on pig farms in southern Portugal and Spain and transmits several important pathogens of humans and livestock. Its distribution is patchy and the determinants of its distribution are uncertain. Here, we use a Bayesian network model to explore possible associations between climate, farm management and the presence of O. erraticus. The resulting network confirms previous suggestions that the presence of O. erraticus is more likely in traditionally constructed pig housing, and indicates that carbon dioxide traps are highly effective for the detection of O. erraticus. Our approach also picked up several other intuitively reasonable relationships, including that traditional housing was more likely to be in poor condition and more likely to be out of use, and that buildings which were in use to house pigs were also less likely to be derelict. Neither temperature nor precipitation had any direct effect on the probability of the presence of O. erraticus, suggesting that the distribution of the species is primarily driven by farm management factors.