Grazing cattle exposure to neighbouring herds and badgers in relation to bovine tuberculosis risk

Landscape as a Shared Space for Badgers and Cattle: Insights Into Indirect Contact and Bovine Tuberculosis Transmission Risk

Though the magnitude of effect is uncertain, badger-cattle indirect contact has been implicated in bovine tuberculosis (bTB) transmission risk to cattle despite a paucity of data on badger space use. This study tracked field use by 35 GPS-collared bTB test-negative badgers (n = 3738 locational fixes, average fixes/badger = 107) and cattle grazing regimes at 446 fields over one grazing season (May-November 2016) on 18 farms (n = 56,202 field-days). Individual badger visits spanned on average 3 farms (max. 9 farms). Badgers entered fields when occupied by grazing cattle on 20% of field-days (nights). Most individual badgers (n = 25; 71%) were recorded in the same field as cattle on multiple occasions (up to 124 field-days each). There was substantial interindividual variation, with 29% of badgers (n = 10) never co-occurring with cattle. Badger field use was positively associated with dairy (rather than beef) production (especially when grazing cattle were present) and with fodder and rough grazing fields (compared with improved pasture and 'other' cattle-related land use). Badgers were recorded in larger fields (range 0.06 to 10.9 ha) more frequently, especially when not actively grazed. They were significantly less likely to use fields with calves compared to fields containing cattle of other age groups. The presence of a badger sett in a field increased the likelihood of field use by tracked badgers. Farm management that minimises cattle-badger indirect contact in fields with setts may reduce bTB transmission risk to cattle. Delaying grazing of fodder fields after (silage) harvest until sward length has increased, restricting grazing to improved pastures, keeping calves with cows longer, or ensuring all batches of cattle have at least some calves present and not grazing fields with badger setts (or fencing around setts to prevent cattle access) may provide simple, cost-effective strategies to reduce indirect badger-cattle contact, thus potentially lowering bTB transmission risk.

Contribution of herd management, biosecurity, and environmental factors to the risk of bovine tuberculosis in a historically low prevalence region

Eradication of bovine tuberculosis (bTB) in certain historically low-prevalence regions remains elusive. A complete characterisation of the husbandry practices, biosecurity, and environment where farms are located is crucial to implement targeted in-farm risk mitigation protocols. Here, a detailed survey performed in 94 dairy cattle farms located in Navarra, a low-prevalence region of Spain between 2016 and 2020 was carried out. Data on 73 biosecurity, farm-, and environmental-level factors potentially associated with the risk of bTB occurrence were evaluated using an ordinal logistic regression model: farms were classified based on their prevalence index, a score linked to each farm to account for the severity and recurrence of bTB cases: 22.3% of the farms had a score of 1, 21.3% a score of 2, 26.6% a score of ≥ 3, and 29.8% were negative herds. A statistically significant association between a higher prevalence index and the frequency of badger sightings along with the lease of pastures to sheep during Winter was identified. Farms that detected badgers on a monthly to daily basis in the surroundings and those that leased pastures for sheep flocks during Winter were four [odds ratio, 95% CI (4.3; 1.1-17.5)] and three (3.1; 1.0-9.9) times more likely to have the highest prevalence index, respectively (predicted probabilityprevalence index≥3 = 0.7; 95% CI 0.3-0.9). Conversely, farms that used a vehicle to transport animals from holdings to pastures were less likely (0.1; <0.1-0.3) to present higher levels of prevalence index compared with farms that used none (on foot). Results suggested that the combined effect of farm- and environmental-level risk factors identified here may be hampering disease eradication in Navarra, highlighting the need to implement targeted protocols on farms and grazing plots. An increased awareness of monitoring sheep and wildlife in direct or indirect contact with cattle herds in historically low bTB prevalence areas should be raised.

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

The European badger, Meles meles, is an important wildlife host for Mycobacterium bovis and contributes to the epidemiology of bovine tuberculosis (bTB) in cattle in several countries. The control of zoonotic diseases, such as bTB, is a central component of global One-Health strategies. Such strategies are complicated by human-wildlife conflicts, particularly where wildlife reservoirs are legally protected. The contrasting objectives of disease management and wildlife conservation, therefore, can require significant investment in research to support evidence-based policies. In Britain and Ireland, for example, badgers are a legally protected species but are also subject to lethal control and vaccination for disease management. In this paper, we review recent (2012-2022) advances in research on this wildlife host on the island of Ireland, which is used to underpin national policies and identify research gaps. In recent years, significant advances in estimating key parameters related to badger management and population dynamics have been made, including estimating population abundance at varying scales (local, landscape, and national). Advances in tracking technology, integrated with mark-recapture and modelling tools, have provided significant insights into the movement ecology of badgers and their interactions with cattle. The adaptation of genetic technologies has improved our understanding of the transmission dynamics of M. bovis among different hosts. As a disease management strategy, the culling of badgers to control bTB has reduced badger densities significantly, although this is not considered a sustainable sole long-term solution to the problem of spillback infection. The recent development of vaccination strategies presents an additional approach to control the disease in wild populations. These types of interventions will require significant applied research to ensure they are sustainable and to maximise benefits. It is also expected that focused research efforts will improve human-wildlife coexistence in the context of the broader One-Health strategy.

Relationship between ambient temperature at sampling and the interferon gamma test result for bovine tuberculosis in cattle

Bovine tuberculosis (bTB) is a disease of significant economic and zoonotic importance, therefore, optimising tests for the identification of Mycobacterium bovis infected cattle is essential. The Interferon Gamma (IFN-γ) Release Assay (IGRA) can diagnose M. bovis infected cattle at an early stage, is easy to perform and can be used alongside skin tests for confirmatory purposes or to increase diagnostic sensitivity. It is known that IGRA performance is sensitive to environmental conditions under which samples are taken and transported. In this study, the association between the ambient temperature on the day of bleeding and the subsequent IGRA result for bTB was quantified using field samples from Northern Ireland (NI). Results of 106,434 IGRA results (2013-2018) were associated with temperature data extracted from weather stations near tested cattle herds. Model dependent variables were the levels of IFN-γ triggered by avian purified protein derivative (PPDa), M. bovis PPD (PPDb), their difference (PPD(b-a)) as well as the final binary outcome (positive or negative for M. bovis infection). IFN-γ levels after both PPDa and PPDb stimulation were lowest at the extremes of the temperature distribution for NI. The highest IGRA positive probability (above 6%) was found on days with moderate maximum temperatures (6-16 °C) or moderate minimum temperatures (4-7 °C). Adjustment for covariates did not lead to major changes in the model estimates. These data suggest that IGRA performance can be affected when samples are taken at high or low temperatures. Whilst it is difficult to exclude physiological factors, the data nonetheless supports the temperature control of samples from bleeding through to laboratory to help mitigate post-collection confounders.

Northern Ireland farm-level management factors for recurrent bovine tuberculosis herd breakdowns

Bovine tuberculosis (bTB) is a chronic, infectious and zoonotic disease of domestic and wild animals caused mainly by Mycobacterium bovis. This study investigated farm management factors associated with recurrent bTB herd breakdowns (n = 2935) disclosed in the period 23 May 2016 to 21 May 2018 and is a follow-up to our 2020 paper which looked at long duration bTB herd breakdowns. A case control study design was used to construct an explanatory set of farm-level management factors associated with recurrent bTB herd breakdowns. In Northern Ireland, a Department of Agriculture Environment and Rural Affairs (DAERA) Veterinarian investigates bTB herd breakdowns using standardised guidelines to allocate a disease source. In this study, source was strongly linked to carryover of infection, suggesting that the diagnostic tests had failed to clear herd infection during the breakdown period. Other results from this study associated with recurrent bTB herd breakdowns were herd size and type (dairy herds 43% of cases), with both these variables intrinsically linked. Other associated risk factors were time of application of slurry, badger access to silage clamps, badger setts in the locality, cattle grazing silage fields immediately post-harvest, number of parcels of land the farmer associated with bTB, number of land parcels used for grazing and region of the country.

Investigating Farm Fragmentation as a Risk Factor for Bovine Tuberculosis in Cattle Herds: A Matched Case-Control Study from Northern Ireland

Bovine tuberculosis remains a challenging endemic pathogen of cattle in many parts of the globe. Spatial clustering of Mycoacterium bovis molecular types in cattle suggests that local factors are the primary drivers of spread. Northern Ireland’s agricultural landscape is comprised of highly fragmented farms, distributed across spatially discontinuous land parcels, and these highly fragmented farms are thought to facilitate localised spread. We conducted a matched case control study to quantify the risks of bovine tuberculosis breakdown with farm area, farm fragmentation, fragment dispersal, and contact with neighbouring herds. Whilst our results show small but significant increases in breakdown risk associated with each factor, these relationships were strongly confounded with the number of contiguous neighbours with bovine tuberculosis. Our key finding was that every infected neighbour led to an increase in the odds of breakdown by 40% to 50%, and that highly fragmented farms were almost twice as likely to have a bTB positive neighbour compared to nonfragmented farms. Our results suggest that after controlling for herd size, herd type, spatial and temporal factors, farm fragmentation increasingly exposes herds to infection originating from first-order spatial neighbours. Given Northern Ireland’s particularly fragmented landscape, and reliance on short-term leases, our data support the hypothesis that between-herd contiguous spread is a particularly important component of the region’s bovine tuberculosis disease system.