AUTHOR=Byrne Andrew W. , Graham Jordon , Milne Georgina , Guelbenzu-Gonzalo Maria , Strain Sam 

TITLE=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

JOURNAL=Frontiers in Veterinary Science

VOLUME=6

YEAR=2019

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2019.00030

DOI=10.3389/fvets.2019.00030

ISSN=2297-1769

ABSTRACT=<p><bold>Background:</bold> Bovine tuberculosis (bTB; <italic>Mycobacterium bovis</italic>) remains a significant problem in a number of countries, and is often found where <italic>M. avium</italic> subsp. <italic>paratuberculosis</italic> (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.</p><p><bold>Methods:</bold> 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 <italic>M. bovis</italic> 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.</p><p><bold>Results:</bold> 45.2% (<italic>n</italic> = 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 &gt;2 samples, to aOR:3.863 at &gt;10 samples), however the estimated CI increased as <italic>N</italic> 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).</p><p><bold>Discussion:</bold> 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.</p>