Abstract
The persistence of bovine tuberculosis (bTB) in certain cattle herds is a major concern in countries pursuing disease eradication worldwide. The chronic nature of the disease, the lack of performance of diagnostic tools, and the presence of wildlife reservoirs may lead infected herds to require longer periods to achieve the officially tuberculosis-free (OTF) status. Here, we evaluated the impact of farm and breakdown characteristics on the probability of disease persistence in infected farms in Castilla y Leon, a bTB-endemic region of Spain, using survival and logistic regression models. Data from bTB breakdowns occurring in 3,550 bTB-positive herds detected in 2010–2017 were analyzed. A multivariable Cox proportional hazards model was fitted using time to recover OTF status as the response variable, and a multivariable logistic regression model using the chronic status (yes/no) for herds experiencing particularly long breakdowns as the outcome variable was also used. Both analyses revealed that county-level bTB herd prevalence, herd size, number of incoming animals in the previous 3 years, number of skin test reactors in the disclosing test, and number of days between the disclosing and follow-up tests were associated with increased breakdown duration. Production type was not consistently associated with chronic infection, suggesting that once infected, it is not a significant predictor of outbreak duration beyond the initial stages of the breakdown. Province-level location and number of animals that are bacteriology-positive also affected significantly the expected herd breakdown duration, but their effect became less significant over time. Risk factors identified in this study may help to identify herds more prone to suffer chronic bTB infection that may require additional control measures early on in a breakdown.
Highlights
Bovine tuberculosis is a zoonotic disease affecting cattle caused by members of the Mycobacterium tuberculosis complex, mainly Mycobacterium bovis and Mycobacterium caprae, which has a major impact in the economy of affected countries due to its effect on trade
The persistence of bTB in certain cattle herds in terms of either herd recurrence or prolonged periods of restriction is a major problem in countries pursuing disease eradication worldwide
Among the factors that may substantially extend the time to recover officially tuberculosis-free (OTF) status and hamper eradication programs are the chronic nature of the disease, the presence of wildlife reservoirs, and the lack of performance of diagnostic tools
Summary
Bovine tuberculosis (bTB) is a zoonotic disease affecting cattle caused by members of the Mycobacterium tuberculosis complex, mainly Mycobacterium bovis and Mycobacterium caprae, which has a major impact in the economy of affected countries due to its effect on trade. Accurate diagnosis of bTB in live animals is often difficult, and several factors that influence test performance and can lead to possible diagnostic failures have been identified. These include the intrinsic limited sensitivity of currently available tests, the choice of the diagnostic cutoff, the test procedure, the disease stage of infected animals, the possible desensitization to the test in the case of the skin test, the existence of host or pathogen genetic variations, the occurrence of cross-reactions, and the effect of concurrent infections [5,6,7,8]. Other factors that impede disease eradication are survival and persistence of M. bovis in the environment and the aggregation at communal water and food sources that can promote closer contacts between cattle and may increase the likelihood of contact with infected wildlife reservoirs [9]
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