Is There a Relationship Between Bovine Tuberculosis (bTB) Herd Breakdown Risk and Mycobacterium avium subsp. paratuberculosis Status? An Investigation in bTB Chronically and Non-chronically Infected Herds
Date
2019-02-14
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Publisher
Frontiers Media
Abstract
Background: Bovine tuberculosis (bTB; Mycobacterium bovis) remains a significant
problem in a number of countries, and is often found where M. avium subsp. paratuberculosis (MAP) is also present. In the United Kingdom, bTB has been difficult
to eradicate despite long-term efforts. Co-infection has been proposed as one partial
mechanism thwarting eradication.
Methods: A retrospective case-control study of 4,500 cattle herds in Northern Ireland,
where serological testing of cattle for MAP, was undertaken (2004–2015). Blood samples
were ELISA tested for MAP; infection of M. bovis was identified in herds by the comparative tuberculin test (CTT) and through post-mortem evidence of infection. Case-herds were those experiencing a confirmed bTB breakdown; control-herds were not experiencing a breakdown episode at the time of MAP testing. A second model included additional testing data of feces samples (culture and PCR results) to better inform herd MAP status. Multi-level hierarchical models were developed, controlling for selected confounders. A sensitivity analysis of the effect of MAP sample numbers per event and the prior timing of tuberculin-testing was undertaken.
Results: 45.2% (n = 250) of case observations and 36.0% (3,480) of control observations were positive to MAP by ELISA (45.8% and 36.4% when including ancillary
fecal testing, respectively). Controlling for known confounders, the adjusted odds ratio
(aOR) for this association was 1.339 (95%CI:1.085–1.652; including ancillary data aOR:1.356;95%CI:1.099–1.673). The size-effect of the association increased with the
increasing number of samples per event used to assign herd MAP status (aOR:1.883 at
>2 samples, to aOR:3.863 at >10 samples), however the estimated CI increased as N
decreased. 41.7% of observations from chronic herds were MAP serology-positive and
32.2% from bTB free herds were MAP positive (aOR: 1.170; 95%ci: 0.481–2.849).
Discussion: Cattle herds experiencing a bTB breakdown were associated with
increased risk of having a positive MAP status. Chronic herds tended to exhibit higher
risk of a positive MAP status than bTB free herds, however there was less support for this association when controlling for repeated measures and confounding. MAP co-infection may be playing a role in the success of bTB eradiation schemes, however further studies are required to understand the mechanisms and to definitively establish causation.
Description
Publication history: Accepted - 23 January 2019; Published - 14 February 2019.
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Citation
Byrne, A. W., Graham, J., Milne, G., Guelbenzu-Gonzalo, M. and Strain, S. (2019) ‘Is There a Relationship Between Bovine Tuberculosis (bTB) Herd Breakdown Risk and Mycobacterium avium subsp. paratuberculosis Status? An Investigation in bTB Chronically and Non-chronically Infected Herds’, Frontiers in Veterinary Science. Frontiers Media SA, 6. doi: 10.3389/fvets.2019.00030.