Behaviour of European badgers and non-target species towards candidate baits for oral delivery of a tuberculosis vaccine
Introduction
In parts of the UK and the Republic of Ireland, the European badger Meles meles is a wildlife reservoir for Mycobacterium bovis the causative agent of bovine tuberculosis (TB) in cattle (Krebs, 1997, Griffin et al., 2005, Palmer et al., 2012). The parenteral vaccination of badgers with Bacillus Calmette-Guerin (BCG) is one current approach for managing the disease in badger populations, with the aim of reducing infection risk to cattle (Chambers et al., 2014). Badgers can be captured and BCG administered via intra-muscular injection, which has been demonstrated to reduce the severity and progression of disease (Chambers et al., 2011, Carter et al., 2012). An alternative and potentially cheaper approach for widespread vaccine delivery is through oral vaccination, with BCG contained within edible baits (Delahay et al., 2003, Robinson et al., 2012). Oral delivery of BCG to wild possums has been shown to produce a protective response, with reduced bacterial counts compared to control animals (Tompkins et al., 2013). Oral vaccination has also been used successfully to control sylvatic rabies and classical swine fever in wild boar (Rossi et al., 2015).
The development of an oral vaccine requires the design and refinement of several components, including the immunogen itself, the bait/delivery system and the methodology for vaccine deployment (Cross et al., 2007). Oral administration to badgers of BCG in solution has been shown to have a protective effect against experimental challenge with M. bovis (Murphy et al., 2014), and is currently the only candidate for the oral vaccination of wild badgers (Chambers et al., 2014). As BCG, an attenuated strain of M. bovis needs to be alive to be effective as a vaccine, any bait used as a delivery system will need to retain BCG viability up to the point of ingestion.
Badgers live in groups that occupy burrow systems known as setts. A badger oral vaccine will therefore most likely be deployed at badger setts (Delahay et al., 2003, Chambers et al., 2014). Previous research by Robertson et al. (2015) used camera footage to investigate which potential non-target species were present at badger setts and whether they would investigate two simple bait types which are attractive to badgers. This earlier work demonstrated that badger setts are occupied and visited by a wide range of other animal species, particularly rodents which are relatively common and likely to consume deployed baits (Robertson et al., 2015). An oral badger vaccine will ideally consist of a bait and a deployment strategy which together are attractive to badgers, but are ideally less so for non-target species.
To support the development and ultimate licensing of and oral badger vaccine we investigated the behaviour of badgers and non-target wildlife species towards three candidate bait designs for the oral delivery of BCG to badgers. The three candidates varied in their construction and presentation (packaging). Although packaging is unlikely to improve bait attractiveness, it prolongs the environmental stability and integrity of the bait (Gowtage et al., personal communication). Packaging also provides a surface for a written label which is a regulatory requirement for licensing a vaccine. We investigated whether packaging and bait design influenced attractiveness to badgers and non-target species (primarily rodents). By measuring variation in bait removal rates amongst badger setts (social groups) and over time we also obtained information to inform the development of an optimal deployment strategy to maximise bait uptake and vaccine coverage.
Section snippets
Study area
The field study was carried out over ten consecutive nights from the 6th to the 16th August 2013 in Gloucestershire, southwest England. Sixteen main setts (conspicuous burrow systems occupied by badger social groups) were selected for the study, based on the presence of field signs during preliminary surveys, indicating there were badgers present. The sixteen setts were spread across an area of approximately 170 km2 (centred around 51°54′N, 2°10′E) where no previous bait, feeding or trapping
Bait removal by badgers
Bait removal was ascribed to badgers (i.e. tiles were moved and bait was taken) at nine of the 16 badger setts (66%) where baits were deployed (Table 1). At four of the seven setts where no baits were taken by badgers, no footage of badgers was obtained from the remote monitoring cameras (Table 1). As a consequence, these four setts were removed from analyses relating to bait removal on the basis that no badgers were actually present at these setts.
Across the 12 setts with evidence of badger
Badger behaviour towards different bait types
Despite differences in packaging and bait design we did not observe a detectable preference by badgers for any of the bait types deployed tested, including the positive control. Levels of removal from under tiles were almost identical for all bait types and the camera footage did not detect consistent preference behaviour towards certain bait types. This result is encouraging for furthering the development of an oral badger vaccine for licensing, for two reasons. First, it suggests that badgers
Conclusion
This study suggests that badgers that take baits will readily take any of the candidate vaccine bait designs being considered for a licensed oral badger vaccine. Moreover, and in agreement with previous studies, it suggests that interference by non-target wildlife species is unlikely to have a significant effect on uptake of baits by badgers, particularly if baits are packaged. Changes in bait removal over time suggest that a period of ‘pre-feeding’ may act to improve vaccine uptake. However,
Acknowledgements
We are indebted to the land owners and tenants for granting access to their land to conduct this study. We would like to thank NWMC field staff, particularly Paul Spyvee and Sarah Boxall for identifying badger setts for the study and Josh Flatman and Alex Wielochowski for their help with bait deployment and data collection. We also thank APHA Weybridge staff for their assistance in assembling the baits used in this study. This research was funded by the Department for Environment, Food and
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