ARTICLE | doi:10.20944/preprints202008.0634.v1
Subject: Medicine & Pharmacology, Veterinary Medicine Keywords: bovine TB; risk factors; disease control; animal health policy; veterinary epidemiology; evidence-based policy
Online: 28 August 2020 (11:25:31 CEST)
Bovine tuberculosis (bTB) outbreaks, caused by Mycobacterium bovis infection, are a costly animal health challenge. Understanding factors associated with the duration of outbreaks, known as breakdowns, could lead to better disease management policy development. We undertook a retrospective observational study (2012-2018) and employed Finite Mixture Models (FMM) to model the outcome parameter, and to investigate how factors were associated with duration for differing subpopulations identified. In addition to traditional risk factors (e.g. herd size, bTB history), we also explored farm geographic area, parcels/farm fragmentation, metrics of intensity via nitrogen loading, and whether herds were designated controlled beef finishing units (CBFU) as potential risk factors for increased duration. The final model fitted log-normal distributions, with two latent classes (k) which partitioned the population into a subpopulation around the central tendency of the distribution, and a second around the tails of the distribution. The latter subpopulation included longer breakdowns of policy interest. Increasing duration was positively associated with recent (<3 yrs) TB history and the number of reactors disclosed, (log) herd size, beef herd-type relative to other herd types, number of land parcels, area, and being designated a controlled finishing unit (“feedlot”), and having high annual inward cattle movements within the “tails” subpopulation. Breakdown length was negatively associated with year of commencement of breakdown (i.e. a decreasing trend) and non-significantly with the organic nitrogen produced on the farm (N kg/hectare), a measure of stocking density. The latter finding may be due to confounding effects with herd size and area. Most variables contributed only moderately to explaining variation in breakdown duration, that is, they had moderate size effects on duration. Herd-size and CBFU had greater effect sizes on the outcome. The findings contribute to evidence-based policy formation in Ireland.
ARTICLE | doi:10.20944/preprints202201.0325.v1
Subject: Biology, Other Keywords: Farm fragmentation; bTB; bovine tuberculosis; Northern Ireland; local spread; neighbourhood; matched case-control; conacre
Online: 21 January 2022 (13:08:45 CET)
Bovine tuberculosis (bTB) 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 farming structures are thought to facilitate localised spread. We conducted a matched case control study to quantify the risks of bTB 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 of farm fragmentation, farm area, fragment dispersal, and contact with neighbouring herds, these relationships were strongly confounded with the number of contiguous neighbours with bTB. 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 non-fragmented 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 NI’s particularly fragmented landscape, and reliance on short-term leases, our data supports the hypothesis that between-herd contiguous spread is a particularly important component of NI’s bTB disease system.