Abstract
The deployment of baits containing vaccines or toxins has been used successfully in the management of wildlife populations, including for disease control. Optimisation of deployment strategies seeks to maximise uptake by the targeted population whilst ensuring cost-effectiveness. Tuberculosis (TB) caused by infection with Mycobacterium bovis affects a broad range of mammalian hosts across the globe, including cattle, wildlife and humans. The control of TB in cattle in the UK and Republic of Ireland is hampered by persistent infection in European badgers (Meles meles). The present study aimed to determine the best strategy for maximising uptake of an oral vaccine by wild badgers, using a surrogate novel bait deployed at 40 badger social groups. Baits contained a blood-borne biomarker (Iophenoxic Acid, IPA) in order to measure consumption in badgers subsequently cage trapped at targeted setts. Evidence for the consumption of bait was found in 83% (199/240) of captured badgers. The probability that badgers had consumed at least one bait (IPA >10 μg ml-1) was significantly higher following deployment in spring than in summer. Lower uptake amongst social groups where more badgers were captured, suggested competition for baits. The probability of bait consumption was significantly higher at groups where main and outlier setts were provided with baits than at those where outliers were present but not baited. Badgers captured 10–14 days post bait feeding had significantly higher levels of bait uptake compared to those caught 24–28 days later. Uptake rates did not vary significantly in relation to badger age and whether bait was placed above ground or down setts. This study suggests that high levels of bait uptake can be achieved in wild badger populations and identifies factors influencing the potential success of different deployment strategies. The implications for the development of an oral badger vaccine are discussed.
Highlights
The deployment of baits is carried out routinely in many countries to deliver vaccines, toxicants, fertility control agents or medication to wildlife populations [1, 2]
The present study showed that bait uptake was higher at groups fed in late spring than in those fed later in the summer, which could be linked with temporal variation in food availability
An oral bait holds the best prospect for delivering vaccine to badgers over a wide geographical area and considerable resources are being directed towards the development and licensing of such a product
Summary
The deployment of baits is carried out routinely in many countries to deliver vaccines, toxicants, fertility control agents or medication to wildlife populations [1, 2]. Field trials of both parenteral [14] and oral [15] delivery have indicated a reduced likelihood of TB infection in both vaccinated and unvaccinated animals; the latter by means of a herd immunity effect. As the delivery of BadgerBCG by cage-trapping and injection is labour intensive, there has been considerable investment in the development of a candidate oral bait for BCG delivery [16,17,18] which may offer a more cost-effective means of vaccinating badgers at a wider scale. The potential contribution of an oral vaccine to TB control was highlighted by a recent study which provided field evidence for a significant protective effect of oral BCG administration in a wild badger population [15]
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