Abstract
BackgroundField vaccination trials with Mycobacterium bovis BCG, an attenuated mutant of M. bovis, are ongoing in Spain, where the Eurasian wild boar (Sus scrofa) is regarded as the main driver of animal tuberculosis (TB). The oral baiting strategy consists in deploying vaccine baits twice each summer, in order to gain access to a high proportion of wild boar piglets. The aim of this study was to assess the response of wild boar to re-vaccination with BCG and to subsequent challenge with an M. bovis field strain.ResultsBCG re-vaccinated wild boar showed reductions of 75.8% in lesion score and 66.9% in culture score, as compared to unvaccinated controls. Only one of nine vaccinated wild boar had a culture-confirmed lung infection, as compared to seven of eight controls. Serum antibody levels were highly variable and did not differ significantly between BCG re-vaccinated wild boar and controls. Gamma IFN levels differed significantly between BCG re-vaccinated wild boar and controls. The mRNA levels for IL-1b, C3 and MUT were significantly higher in vaccinated wild boar when compared to controls after vaccination and decreased after mycobacterial challenge.ConclusionsOral re-vaccination of wild boar with BCG yields a strong protective response against challenge with a field strain. Moreover, re-vaccination of wild boar with BCG is not counterproductive. These findings are relevant given that re-vaccination is likely to happen under real (field) conditions.
Highlights
Field vaccination trials with Mycobacterium bovis BCG, an attenuated mutant of M. bovis, are ongoing in Spain, where the Eurasian wild boar (Sus scrofa) is regarded as the main driver of animal tuberculosis (TB)
An attenuated mutant of M. bovis, Mycobacterium bovis BCG, is often the vaccine used in wildlife vaccination trials worldwide [2,3,4,5,6,7,8]
Field vaccination trials are ongoing in Spain, where the Eurasian wild boar (Sus scrofa) is regarded as the main driver of animal TB at the wildlife-livestock interface [10,11,12]
Summary
Field vaccination trials with Mycobacterium bovis BCG, an attenuated mutant of M. bovis, are ongoing in Spain, where the Eurasian wild boar (Sus scrofa) is regarded as the main driver of animal tuberculosis (TB). It has been demonstrated that the most efficient oral vaccine bait deployment strategy in this area consists in using selective piglet feeders and deploying vaccine baits both at the start (late June/early July) and the end of summer (late August/early September), in order to gain access to a high proportion of early and late born wild boar piglets respectively, avoiding the hottest period from late July to early August [14,15]. With this strategy of a double delivery in summer, it would be probable that some individuals gain access to vaccine baits twice in a season. Adverse effects of re-vaccination or overdosage of BCG in wild boar were not expected, we were interested in assessing the effects of re-vaccination with a 52 day interval imitating field conditions
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