Defining and testing a wildlife intervention framework for exotic disease control

Abstract

1. Outbreaks of disease at the wildlife-livestock interface may require management interventions. Where they involve exotic/non-endemic pathogens in wildlife, then such plans may need to be rapidly conceived and implemented to prevent further disease spread. However, detailed information on the distribution of infection is likely to be absent, whilst limited resources and tools, and ethical considerations impose constraints on what is possible and proportionate.2. We describe four considerations to inform decision-making on whether to intervene. With reference to two recent examples (bovine tuberculosis in badgers in an otherwise disease-free area, and African swine fever in wild boar in central Europe), we outline six steps to guide implementation. 3. In both examples, a Disease Control Area was defined by determining a minimum infected area (MIA) and a buffer zone based on wildlife ecology and the potential for unrecorded spread of infection. The total area was the subject of management intervention, with the level of infection used to inform adaptive management.4. The MIA is defined as the minimum area that could contain all infected wildlife, given our current level of information, with a surrounding buffer zone to account for the possibility of further onward spread. In our examples, the zones were defined using a combination of field data and existing knowledge of host spatial organization and movement.5. The MIA (plus buffer zone) approach provides a framework for optimizing the targeting of resources in a proportionate response to a disease outbreak. Where infected animals occur outside the MIA, our examples show how wildlife management has been adapted. In principle, this approach is suitable for the delivery of disease outbreak control in wildlife, whether through culling, vaccination or other forms of control.

Vaccinating badgers in a post‐cull landscape; insights from the field

“…We recommend that costs are closely monitored as vaccination in post-cull badger populations increases in scale; particularly as the badger population recovers in size and more animals become available to vaccinate, which will likely result in falling costs (if using the 'cost to vaccinate a single badger' metric). Recent work has suggested that badger vaccination might become more expensive as the population recovers (and subsequently more doses of vaccine are required) (Smith & Budgey, 2021), however, this potential additional cost may be offset or even reversed if the increased time and effort required to trap badgers in the early years following culling translates into increased costs during this time period. Continuing to collect and regularly analyse trapping data and delivery costs during vaccination operations on previously culled populations is highly recommended, in order to continually optimize trapping and vaccination success as wider rollout progresses.…”

“…to have a protective effect in unvaccinated cubs if a sufficient proportion of the adults in their social group is vaccinated; an example of herd immunity (Carter et al, 2012). Although badger vaccination would be expected to reduce risks of TB transmission to UK cattle, the scale of any benefit is unknown (Smith & Budgey, 2021) and this evidence gap remains a significant obstacle to vaccination rollout at a larger scale (Benton et al, 2020) as it contributes to the generally low level of confidence in badger vaccination within the farming industry (Enticott et al, 2012(Enticott et al, , 2014. Several thousand doses of vaccine have been deployed in badger populations since the BadgerBCG © vaccine (AJVaccines) was licenced in 2010 (Benton et al, 2020), but to date vaccination deployment has been relatively modest in spatial scale with only a very small number of vaccination areas being over 100 km 2 and many operating over areas of less than 20 km 2 .…”

“…Similarly, in the Republic of Ireland culling is used to reduce badger numbers, followed by vaccination to minimize transmission as the badger population recovers (Martin et al, 2020). A recent study used an established simulation model of TB transmission dynamics among badgers (Smith et al, 2012(Smith et al, , 2016 to assess potential exit strategies from intensive badger culling, including vaccination (Smith & Budgey, 2021). Simulations suggested that badger vaccination performed similarly to the other strategies tested (annual supplementary culling, intermittent supplementary culling at a range of intervals, and vaccination combined with fertility control) in reducing the number of infected badgers present.…”

“…In the present study we addressed this knowledge gap by exploiting existing sources of data from one previous and one ongoing culling operation; (1) the randomized badger culling trial (RBCT, a large‐scale government culling trial carried out from 1998 to 2005, Bourne et al, 2007b) and (2) the current industry‐led licenced culls. We also utilized data collected during a vaccine deployment operation in a recently culled badger population (Defra, 2018, Smith et al, 2022). In addition, we conducted workshops with a highly experienced cohort of badger trappers who have undertaken operations in a wide variety of scenarios, with the aim of understanding how field practices might be tailored to trapping badger populations in previously culled populations.…”