Uptake of baits by wild badgers: Influences of deployment method, badger age and activity patterns on potential delivery of an oral vaccine.

In parts of the United Kingdom and Ireland, the European badger is a wildlife host for Mycobacterium bovis (the causative agent of bovine tuberculosis). Badger vaccination is one management option for reducing disease spread. Vaccination is currently achieved by parenteral vaccination of captured badgers, but an oral vaccine delivered in a bait may provide an additional approach in the future. We conducted two field experiments in wild badger populations to identify factors that influence uptake (% of individuals with evidence of bait consumption) of candidate oral vaccine baits. In both instances, baits containing the biomarker iophenoxic acid (as a proxy for the vaccine) were fed at burrows (setts) associated with badger social groups (study A = 48 groups, study B = 40 groups). Badgers were captured following a period of bait deployment to quantify uptake in relation to age, sex and social group. In addition, groups were allocated different treatments and the bait deployment protocol was varied to identify effects on uptake. Study A tested the effects of season, bait type, bait placement and packaging, while study B investigated the effects of bait quantity and badger activity levels. Overall bait uptake was low (Study A = 24 %, Study B = 37 %) but this varied among treatment groups (range 0-58 %). In both studies, bait uptake was significantly higher in cubs than in adults. Uptake was substantially higher where baits were placed directly into sett entrances (rather than under tiles near setts), and by badgers caught at main setts rather than at outlier setts. Season, bait type and packaging did not influence uptake, while increasing the quantity of bait available increased uptake by cubs but not by adults. Levels of badger activity at setts varied over time (suggesting potential disturbance), but were positively associated with levels of bait uptake.

Dynamic interactions among badgers: implications for sociality and disease transmission.

1. Direct interactions between individuals play an important part in the sociality of group-living animals, their mating system and disease transmission. Here, we devise a methodology to quantify relative rates of proximity interaction from radio-tracking data and highlight potential asymmetries within the contact network of a moderate-density badger population in the north-east of England. 2. We analysed radio-tracking data from four contiguous social groups, collected over a 3-year period. Dynamic interaction analysis of badger dyads was used to assess the movement of individuals in relation to the movement of others, both within and between social groups. Dyads were assessed with regard to season, sex, age and sett use pattern of the badgers involved. 3. Intragroup separation distances were significantly shorter than intergroup separation distances, and interactions between groups were rare. Within groups, individuals interacted with each other more often than expected, and interaction patterns varied significantly with season and sett use pattern. Non-mover dyads (using the main sett for day-resting on > 50% of occasions) interacted more frequently than mover dyads (using an outlier sett for day-resting on > 50% of occasions) or mover-non-mover dyads. Interactions between group members occurred most frequently in winter. 4. Of close intragroup interactions (< 50 m separation distance), 88.6% were associated with a main sett and only 4.4% with outlier setts. Non-mover dyads and non-mover-mover dyads interacted significantly more often at the main sett than mover-only dyads. These results highlight the importance of the main sett to badger sociality and support the suggestion that badger social groups are comprised of different subgroups, in our case based on differential sett use patterns. 5. Asymmetries in contact structure within a population will affect the way in which diseases are transmitted through a social network. Assessment of these networks is essential for understanding the persistence and spread of disease within populations which do not mix freely or which exhibit heterogeneities in their spatial or social behaviour.

Bait uptake by wild badgers and its implications for oral vaccination against tuberculosis.

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.