Abstract
BackgroundDespite great effort and investment incurred over decades to control bovine tuberculosis (bTB), it is still one of the most important zoonotic diseases in many areas of the world. Test-and-slaughter strategies, the basis of most bTB eradication programs carried out worldwide, have demonstrated its usefulness in the control of the disease. However, in certain countries, eradication has not been achieved due in part to limitations of currently available diagnostic tests. In this study, results of in-vivo and post-mortem diagnostic tests performed on 3,614 animals from 152 bTB-infected cattle herds (beef, dairy, and bullfighting) detected in 2007–2010 in the region of Castilla y León, Spain, were analyzed to identify factors associated with positive bacteriological results in cattle that were non-reactors to the single intradermal tuberculin test, to the interferon-gamma (IFN-γ) assay, or to both tests applied in parallel (Test negative/Culture + animals, T-/C+). The association of individual factors (age, productive type, and number of herd-tests performed since the disclosure of the outbreak) with the bacteriology outcome (positive/negative) was analyzed using a mixed multivariate logistic regression model.ResultsThe proportion of non-reactors with a positive post-mortem result ranged from 24.3% in the case of the SIT test to 12.9% (IFN-γ with 0.05 threshold) and 11.9% (95% CI 9.9-11.4%) using both tests in parallel. Older (>4.5 years) and bullfighting cattle were associated with increased odds of confirmed bTB infection by bacteriology, whereas dairy cattle showed a significantly lower risk. Ancillary use of IFN-γ assay reduced the proportion of T-/C + animals in high risk groups.ConclusionsThese results demonstrate the likelihood of positive bacteriological results in non-reactor cattle is influenced by individual epidemiological factors of tested animals. Increased surveillance on non-reactors with an increased probability of being false negative could be helpful to avoid bTB persistence, particularly in chronically infected herds. These findings may aid in the development of effective strategies for eradication of bTB in Spain.
Highlights
Despite great effort and investment incurred over decades to control bovine tuberculosis, it is still one of the most important zoonotic diseases in many areas of the world
Bovine tuberculosis is a zoonotic disease of cattle primarily caused by Mycobacterium bovis and, to a lesser extent, by M. caprae
This study was aimed at quantifying the number of non-reactors to the in-vivo diagnostic tests (SIT and IFN-γ tests) that subsequently produced culture positive results confirming M. bovis or M. caprae infection and the identification of individual and herd factors associated with these false negative results in the in-vivo tests at the animal level
Summary
Despite great effort and investment incurred over decades to control bovine tuberculosis (bTB), it is still one of the most important zoonotic diseases in many areas of the world. Disease eradication at a farm level is considered achievable as long as the integrity of the herd (epidemiological unit) is maintained [11] In this context, a diagnostic test that can accurately differentiate infected from non-infected animals at the individual level in a timely manner is crucial for disease eradication. False positives may have an important economic impact in the eradication programs due to the unnecessary slaughter of healthy animals and undermine the confidence of farmers in the program, while false negatives will maintain the infection in the herd. Their detection is of paramount importance, especially as the overall prevalence of bTB decreases in a herd [9,12]
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