Risk factors associated with negative in-vivodiagnostic results in bovine tuberculosis-infected cattle in Spain

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.

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

“…In addition, there might be risk factors associated with the application of the tests that may influence a negative result even if the animal is truly infected (Alvarez et al, 2014). This situation is particularly problematic in endemic regions or in herds where bTB is chronic because there is a risk of leaving residual infection, making it difficult for a herd to clear infection (Conlan et al, 2012;Gallagher et al, 2013).…”

Effect of the inoculation site of bovine purified protein derivative (PPD) on the skin fold thickness increase in cattle from officially tuberculosis free and tuberculosis-infected herds

“…Breed (Brooks-Pollock et al, 2013), age (Brooks-Pollock et al, 2013;Alvarez et al, 2014), and the individual variability of the animals (Pollock and Neil, 2002;Schiller et al, 2010;Whelan et al, 2010) have been reported as possible host-related causes of an impaired performance of the tests. In addition, the effect of other factors related with the test itself, such as the quality of the PPDs used (Good et al, 2011a,b) and the position where it is inoculated (Monaghan et al, 1994) has been also reported.…”

A cross-sectional study on prevalence of bovine tuberculosis in Indian and crossbred cattle in Gangetic delta region of West Bengal, India

“…The tuberculin tests (SIT and CTT) and γ-IFN assay in cattle were done simultaneously to ensure the reliability of the results as described elsewhere [11]. Based on the test results, the cattle positive to either SIT and γ-IFN assay or CTT and γ-IFN assay was interpreted as positive to BTB.…”