Estimating wildlife vaccination coverage using genetic methods

Abstract

Vaccination is a useful approach for the control of disease in wildlife populations. However, its effectiveness is dependent in part on delivery to a sufficient proportion of the target population. Measuring the proportions of wild animal populations that have been vaccinated is challenging and so there is a need to develop robust approaches that can contribute to our understanding of the likely efficacy of wildlife vaccination campaigns.

We used a modified capture mark recapture technique to estimate vaccine coverage in a wild population of European badgers (Meles meles) vaccinated by live-trapping and injecting with Bacillus Calmette-Guérin as part of a bovine tuberculosis control initiative in Wales, United Kingdom. Our approach used genetic matching of vaccinated animals to a sample of the wider population to estimate the percentage of badgers that had been vaccinated. Individual-specific genetic profiles were obtained using microsatellite genotyping of hair samples, which were collected directly from trapped and vaccinated badgers and non-invasively from the wider population using hair traps deployed at badger burrows (setts).

With two nights of trapping at each sett in an annual campaign, an estimated 50 % (95 % confidence interval 40−60 %) of the badger population received at least one dose of vaccine in a single year. Using a simple population model this suggested that the proportion of the population that would have received at least one dose of vaccine over the course of the four year vaccination campaign was between 67 % and 83 %.

This is the first attempt, outside of field trials, to quantify the level of vaccine coverage achieved by trapping and injecting badgers, which is currently the only option for delivering BCG vaccine to this species. The results therefore have specific application to bTB control policy and the novel approach may have wider value in wildlife management and research.