Disturbance Ecology Meets Bovine Tuberculosis (bTB) Epidemiology: A Before-and-After Study on the Association between Forest Clearfelling and bTB Herd Risk in Cattle Herds

Abstract

Disturbance ecology refers to the study of discrete processes that disrupt the structure or dynamics of an ecosystem. Such processes can, therefore, affect wildlife species ecology, including those that are important pathogen hosts. We report on an observational before-and-after study on the association between forest clearfelling and bovine tuberculosis (bTB) herd risk in cattle herds, an episystem where badgers (Meles meles) are the primary wildlife spillover host. The study design compared herd bTB breakdown risk for a period of 1 year prior to and after exposure to clearfelling across Ireland at sites cut in 2015–2017. The percent of herds positive rose from 3.47% prior to clearfelling to 4.08% after exposure. After controlling for confounders (e.g., herd size, herd type), we found that cattle herds significantly increased their odds of experiencing a bTB breakdown by 1.2-times (95%CIs: 1.07–1.36) up to 1 year after a clearfell risk period. Disturbance ecology of wildlife reservoirs is an understudied area with regards to shared endemic pathogens. Epidemiological observational studies are the first step in building an evidence base to assess the impact of such disturbance events; however, such studies are limited in inferring the mechanism for any changes in risk observed. The current cohort study suggested an association between clearfelling and bTB risk, which we speculate could relate to wildlife disturbance affecting pathogen spillback to cattle, though the study design precludes causal inference. Further studies are required. However, ultimately, integration of epidemiology with wildlife ecology will be important for understanding the underlying mechanisms involved, and to derive suitable effective management proposals, if required.

The European Union One Health 2021 Zoonoses Report

“…In most of the MSs (Greece, Ireland, Spain) and the United Kingdom (Northern Ireland), no significant improvements were observed over time given that these data refer to zones where activities related to eradication programmes are more difficult due to unfavourable local environmental conditions (free‐range animals, common grazing land, transhumance, etc.) (Ciaravino et al., 2021; Byrne et al., 2022). However, in Italy, Spain and Portugal, several zones obtained disease‐free status during this period.…”

“…In the last 10 years (2012–2021), the overall annual number of infected cattle herds reported in the non‐disease‐free zones decreased by 47.5%, whereas prevalence decreased only by 4.2%. These different trends can partly be attributed to (1) the withdrawal of the United Kingdom from the EU; (2) the decreased number of herds; (3) the gradual obtention of disease‐free status in zones within non‐disease‐free MSs and (4) unfavourable environmental conditions hindering the eradication process in several non‐disease‐free zones (Byrne et al., 2022).…”

The European Union One Health 2022 Zoonoses Report

“…These different trends can be attributed for the most part to the withdrawal of the United Kingdom from the EU, to the decreased number of herds (−53.0%), to the gradual progression of DFS in zones within MSs with an approved eradication programme (i.e. UEP) and to unfavourable environmental conditions hindering the eradication process in several UEP zones (de la Cruz et al., 2019 ; Byrne et al., 2022 ).…”

Badger Ecology, Bovine Tuberculosis, and Population Management: Lessons from the Island of Ireland

“…Badger socio-spatial structure was also the focus of "the N11 badger study" [64] in County Wicklow. It investigated whether environmental disturbances, such as landscape change [65][66][67], in this case in the form of roadbuilding, can interfere with badger movement and territoriality in an area of up to 33 km 2 [33]. Such disturbances may enhance the potential for bTB transmission [68] if behaviours change such that infectious contacts are increased between hosts.…”

“…However, the magnitude of the intervention or disturbance may also be important (e.g., selective culling versus proactive culling; clearfelling forests versus forest thinning). Epidemiological research has provided some evidence of an association between landscape disturbance caused by motorway building [72] or clearfelling of the forest [66,67] and cattle herd bTB risk. However, it is not clear how these patterns emerged mechanistically via wildlife disturbance and how they fit within the density-territorial gradient framework (see below).…”