Estimation of Bait Uptake by Badgers, Using Non-invasive Methods, in the Perspective of Oral Vaccination Against Bovine Tuberculosis in a French Infected Area

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.

Keywords: badger (Meles meles); bait deployment; biomarker; bovine tuberculosis; hair trapping; oral vaccination.

Figure 1

Location of the setts selected within the study zone.

Figure 2

Bait produced by Connovation Ltd. (Manukau, New Zealand) used in the study. On the left picture (by Rémi Schmitd), the palatable part (or PT made of peanut butter, cereal, and sugar) appears in red as it also contains Rhodamine B. The white part corresponds to the hardened peanut oil (HPO) where the vaccine, when present, may be inserted in the center. Right picture (by Matthieu Colombe): hair trap and baits deployed in the hole of a badger sett. These baits were previously packed within an YPBFERAL^® paper bag.

Figure 3

Schedule for bait deployment and hair collection in spring (March to April 2018) and summer (July to August 2018). X, pre-baits deployment; +, baits deployment; •, hair collection near setts; ▴, hair collection on pastures.

Figure 4

Mean (± 95% CI) badger activity at social groups in zone A compared to zone B (top panel) and where cubs were detected or not by video surveillance (bottom panel).

Figure 5

Results of the FAMD at the social group level. (A) Graph of the qualitative variables plotted on dimensions 1 and 2. (B) Graph of the quantitative variables plotted on dimensions 1 and 2. (C) Graph of the qualitative variables plotted on dimensions 1 and 3. (D) Graph of the quantitative variables plotted on dimensions 1 and 3.

Figure 6

Results of the FAMD at the pasture level. (A) Graph of the qualitative variables plotted on dimensions 1 and 2. (B) Graph of the quantitative variables plotted on dimensions 1 and 2.