Wildlife disease management in practice: oral vaccination to control wild tuberculosis

Resumen del trabajo presentado a la 12th Conference of the European Wildlife Disease Association (EWDA), celebrada en Berlin (Alemania) del 26 al 31 de agosto de 2016.Disease management in wildlife is crucial in shared diseases with impact in conservation, economy and human health such as animal tuberculosis (TB). We report a field experiment on TB control in wild boar (Sus scrofa) - the main wildlife reservoir in Mediterranean scenarios - through oral vaccination in a highly prevalent area with an increasing TB prevalence trend. The study was conducted in Montes de Toledo (Central Spain) during six years (two control years plus four years vaccinating) and involved 10,000 vaccinated ha and 50,000 control ha. Fifteen sites were used as controls (a mix of private and public hunting estates and protected areas). Vaccinated areas cover two situations: (1) a high initial prevalence (85 %), corresponding to a non-managed Natural Park (NP) and (2) a medium initial prevalence (55 %), corresponding to managed hunting estates (HE). In each of these settings, one site was treated with the life vaccine BCG and another one with a heat-inactivated M. bovis vaccine, IV (total of four treated sites = BCG-NP, IV-NP, BCG-HE, IV-HE). The vaccines were deployed via chemically marked-baits in selective feeders to target wild boar piglets to prevent infection acquisition. Each year summer, 18,000 marked baits were distributed among sites. TB prevalence was assessed by culture and presence of TB compatible lesions in hunter-harvested individuals. Bait uptake, estimated by chemical marker detection in piglets, was 39 % and 77 % in the BCG- and IV- NP sites, and 94 % and 92 % in the BCG- and IV- HE sites. TB prevalence showed a 14 % increase in the control area and a 10 % in BCG-NP, a slight decrease in BCG-HE and IV-NP sites (11 and 12 % respectively) and a 74 % decrease in IV-HE site when comparing initial and final prevalences. The IVHE site reached a 100 % reduction in the incidence rate among piglets and a progressive decrease in prevalence in older age classes during the study period. These results suggest that IV vaccination does not only protect piglets under field conditions, but can achieve an effect at the population scale. Nevertheless, protection seems to be context-dependent as results are different in the high and low initial prevalence setting. This could be due to different bait uptake rates or to the different initial TB prevalence. Our results suggest that IV vaccination might be a useful single tool for TB control in wild boar. Further research will explore its combination with other tools within integrated disease management schemes.Peer Reviewe