Abstract
Although France is officially declared free of bovine tuberculosis (TB), Mycobacterium bovis infection is still observed in several regions in cattle and wildlife, including badgers (Meles meles). In this context, vaccinating badgers should be considered as a promising strategy for the reduction in M. bovis transmission between badgers and other species, and cattle in particular. An oral vaccine consisting of live Bacille Calmette–Guérin (BCG) contained in bait is currently under assessment for badgers, for which testing bait deployment in the field and assessing bait uptake by badgers are required. This study aimed to evaluate the bait uptake by badgers and determine the main factors influencing uptake in a TB-infected area in Burgundy, north-eastern France. The baits were delivered at 15 different setts located in the vicinity of 13 pastures within a TB-infected area, which has been subject to intense badger culling over the last decade. Pre-baits followed by baits containing a biomarker (Rhodamine B; no BCG vaccine) were delivered down sett entrances in the spring (8 days of pre-baiting and 4 days of baiting) and summer (2 days of pre-baiting and 2 days of baiting) of 2018. The consumption of the marked baits was assessed by detecting fluorescence, produced by Rhodamine B, in hair collected in hair traps positioned at the setts and on the margins of the targeted pastures. Collected hairs were also genotyped to differentiate individuals using 24 microsatellites markers and one sex marker. Bait uptake was estimated as the proportion of badgers consuming baits marked by the biomarker over all the sampled animals (individual level), per badger social group, and per targeted pasture. We found a bait uptake of 52.4% (43 marked individuals of 82 genetically identified) at the individual level and a mean of 48.9 and 50.6% at the social group and pasture levels, respectively. The bait uptake was positively associated with the presence of cubs (social group level) and negatively influenced by the intensity of previous trapping (social group and pasture levels). This study is the first conducted in France on bait deployment in a badger population of intermediate density after several years of intensive culling. The results are expected to provide valuable information toward a realistic deployment of oral vaccine baits to control TB in badger populations.
Highlights
The ability of some wild hosts to maintain or transmit pathogens to livestock is often a barrier to control and eradication of many major veterinary diseases, because influencing the wild hosts’ behavior, ecology, and susceptibility to the pathogen is very difficult
The aim of this study was to determine the proportion of badgers that had consumed the baits at three levels: [1] individual, [2] social group, and [3] the pasture level
As we found a similar proportion of negative/positive/inconclusive Rhodamine B (RhB) samples between the ones that lead to a genetic identification and the ones that could not provide a reliable genetic profile, we can reasonably assume that genotyping errors did not influence the final results of bait uptake
Summary
The ability of some wild hosts to maintain or transmit pathogens to livestock is often a barrier to control and eradication of many major veterinary diseases, because influencing the wild hosts’ behavior, ecology, and susceptibility to the pathogen is very difficult. The oral vaccination of wildlife has been an effective strategy to control rabies in red foxes (Vulpes vulpes) and classical swine fever (CSF) in wild boar (Sus scrofa) [3–6]. The French M. bovis host community comprises cattle, badger, wild boar, deer (Cervus elaphus and Capreolus caprelolus), and foxes. Badgers have been identified as spillover hosts, able to transmit the infection to cattle, due to their capacity to excrete M. bovis, the interactions existing between the two species, and the occurrence of identical strains locally in both species [9–11]. In north-eastern France, M. bovis infection persists locally at the farm level in cattle and badgers despite 9 years of badger culling and management measures implemented in cattle. In the context of likely M. bovis transmission from infected badgers to cattle, vaccinating badgers is an attractive tool to limit the transmission of M. bovis within the host community. As for other wildlife vaccines (e.g., rabies and CSF), the oral delivery through bait would be an attractive method to administer the vaccine to badgers relatively
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