Bovine tuberculosis in Northern Ireland: Risk factors associated with time from post-outbreak test to subsequent herd breakdown

Abstract

Compulsory bovine Tuberculosis testing has been implemented since 1959 in NorthernIreland. Initial rapid progress in the eradication of the disease was followed by a situation where disease levels tended to fluctuate around a low level. This study Tuberculin Test (SICTT) reactors at disclosure test), local bTB prevalence, herd size and type were identified as significant risk factors (p<0.05), as was the purchase of higher numbers (n>27 per year) of cattle. Consistent with other studies this work shows bTB confirmation to not be predicative of a future herd breakdown. This work shows bTB history as not being a risk factor for a future breakdown. This result could be reflective of the exclusion criteria used in the study, which may have selected for incidents where historical status was of less importance.

Risk of tuberculosis cattle herd breakdowns in Ireland: effects of badger culling effort, density and historic large-scale interventions

“…We purposely used a simple metric for a history of bTB infection (similar to [3]) as we only wanted to control for this known risk factor. However, we acknowledge that the relationship between current risk and previous history may be complex, and highlight other more in-depth analysis of this issue [37,40,41]. …”

A review of risk factors for bovine tuberculosis infection in cattle in the UK and Ireland

“…In Italy, enterprises consisting of both dairy and beef animals, presented a greater risk [odds ratio (OR) 4•92, 95% CI 1 •26-19•19] than exclusively dairy enterprises, attributed to differences in purchasing policy [78]. Dairy herds experienced a recurrent bTB incident sooner than non-dairy herds in Northern Ireland, even after controlling for herd size [82], but a similar study in Ireland showed that dairy animals had a lower risk of a future restriction [83]. GB surveillance data indicate that the relationship between bTB incidence rate and herd type may be a result of the larger sizes of dairy herds and their location [84].…”

Risk factors for failure to detect bovine tuberculosis in cattle from infected herds across Northern Ireland (2004–2010)

“…However, dairy herds have been found to be a risk factor for herd bTB breakdown and the risk of recurrence in Northern Ireland (Doyle et al, 2014), and of increased risk of disclosing a LRS in the Republic of Ireland (Olea-Popelka et al, 2008). O'Hagan et al (2015) looked at the probability of SCITT positive animals being confirmed with bacteriology in NI, and found that dairy herds were significantly more likely to be confirmed than non-diary.…”

“…This indicates that the dairy herds may be particularly vulnerable to having SCITT tests that underperform both in their ability to detect true positives and false negatives (O'Hagan et al, 2015). This problem of non-detection of truly infected dairy animals may be a partial explanation for the shorter times to breakdown observed in such herds in NI, as it may represent within-herd residual infection (Doyle et al, 2014;Lahuerta-Marin et al, 2015). Moreover, it has been described that bTB can spread faster in dairy herds than in beef herds (Alvarez et al, 2012b).…”

“…Herd size has been found to be a significant risk factor for bTB disclosure and herd breakdown risk in a number of studies (Brooks-Pollock and Keeling, 2009;Byrne et al, 2014;Doyle et al, 2014;Skuce et al, 2010). Herd size may contribute to increased bTB risk due to the potential for increased residual infection, especially if tests can behave differentially across herd sizes.…”