Bovine tuberculosis history as a risk factor for recurrence in English cattle herds experiencing a breakdown.

BACKGROUND

Bovine tuberculosis (TB) threatens cattle farming in England. Supplementing tuberculin skin testing with the interferon-gamma blood test during TB incident (breakdown) management can enhance diagnostic sensitivity. We aimed to identify herds at greater risk of recurrence depending on their recent TB history to inform targeted interferon-gamma test deployment.

METHODS

Using observational data, we analysed TB breakdowns in herds with a lesion-positive or bacteriologically positive (officially tuberculosis free-withdrawn [OTF-W]) breakdown in the High-Risk Area or six-monthly surveillance section of the Edge Area of England between 2018 and 2020. Multivariable logistic regression assessed the odds of recurrence 18 months post-breakdown, based on TB status in the 18 months prior (OTF-W, OTF-suspended [OTF-S], none). Covariates previously identified as recurrence risk factors were included.

RESULTS

Herds with an OTF-W breakdown history had significantly higher odds of recurrence than those with no history: odds ratio [OR] 1.3 (95% confidence interval [CI]: 1.1‒1.6). OTF-S history did not confer increased risk: OR 0.9 (95% CI: 0.8‒1.1). A large herd size was another significant risk factor for recurrence.

LIMITATIONS: Limited covariates were included in the analysis, which means that other factors potentially driving the recurrence of disease within herds may have been overlooked.

CONCLUSION

This analysis supports prioritising interferon-gamma testing of OTF-W breakdown herds with an OTF-W history but not an OTF-S history. Large herds, irrespective of breakdown history, may also benefit. Effective interventions against TB recurrence require further investigation.