Abstract

Bovine tuberculosis (bTB) is an important re-emerging zoonotic disease, causing major economic losses and constraining international trade of animals and their products. Despite evidence that genetic factors may influence resistance to bTB in cattle, this aspect remains unstudied in natural populations. In order to investigate the relative importance of genetic heterozygosity in determining susceptibility to bTB infection in natural populations of wild boar, we studied 177 wild boars from eight estates in Southern Spain with different wild boar density and bTB prevalence. Each individual was assessed for age class, sex, and bTB infection. Disease dissemination (spread of lesions within an animal) was determined following anatomopathological examination. We used a panel of 20 microsatellite markers previously cloned from domestic pigs to calculate each individual’s ‘internal relatedness’ (IR), a derivative of heterozygosity which estimates parental similarity. An initial analysis revealed a significant association between bTB infection and IR—relatively less heterozygous (= high IR) wild boars being more likely to be infected (GLM, F_1,170=8.96, p<0.003).

A more complicated model incorporating age, wild boar density, and estate management practices showed that bTB infection was strongly associated with IR and age (both p<0.0005), and less strongly with abundance (p<0.005). Testing each marker separately revealed evidence of a disproportionate effect on bTB susceptibility associated with chromosomes 7q and 13q, regions with plausible connections to immune function. Our results show that regardless of differences in management practices, genetic heterozygosity is a key predictor of both infection and disease progression. This study provides the first convincing evidence of genetic factors influencing the maintenance and severity of bTB in natural populations.