Abstract
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 years) TB history and the number of reactors disclosed, (log) herd size, beef herd-type relative to other herd types, number of land parcels, area, being designated a CBFU (“feedlot”) and having high annual inward cattle movements within the “tails” subpopulation. Breakdown length was negatively associated with the 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.
Highlights
Bovine tuberculosis remains a priority pathogen of cattle in Ireland [1,2] and elsewhere [3,4,5,6]and one that expends considerable resources from farmers, the state, and, for member states, the EUPathogens 2020, 9, 815; doi:10.3390/pathogens9100815 www.mdpi.com/journal/pathogensCommission
A key challenge is to ensure that disease policy is evidence-based and adapts in response to changes in risk patterns so that programme effectiveness is maximised and stakeholders can be assured that decisions affecting them are underpinned by a coherent epidemiological analysis of the data [8]
The increase in dairy production has been associated with an increase in stocking density and herd size, while studies characterised the scale of cattle movements within Ireland [12], it is unclear whether the nature of how these factors relate to TB risk has changed in that period [13]
Summary
Bovine tuberculosis remains a priority pathogen of cattle in Ireland [1,2] and elsewhere [3,4,5,6]and one that expends considerable resources from farmers, the state, and, for member states, the EUPathogens 2020, 9, 815; doi:10.3390/pathogens9100815 www.mdpi.com/journal/pathogensCommission. Understanding risk factors associated with prolonged duration can be of benefit to tailoring policy to local conditions, with the intentions of reducing the spread of infection within and between herds. In Ireland, a significant expansion of the dairy sector took place from 2015 onwards following the removal of EU milk quotas, with an increase of 54% in milk production from 2005 to 2018 [11]; this has been temporally correlated with an increase in TB herd incidence. The increase in dairy production has been associated with an increase in stocking density and herd size, while studies characterised the scale of cattle movements within Ireland [12], it is unclear whether the nature of how these factors relate to TB risk has changed in that period [13]. Data from Britain suggest such movement increases may increase inter-herd M. bovis spread [14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
