Effect of Mycobacterium avium subsp. paratuberculosis (MAP) infection on the diagnostic accuracy for Mycobacterium bovis (M. bovis) infection under field conditions in cattle belonging to low M. bovis prevalence herds

Abstract

Currently, the Chilean authority has implemented a National Eradication Program for bovine tuberculosis (bTB), aimed at controlling and eradicating the disease in Chile. The area under study has a low within-herd prevalence, has a relatively low number of infected herds, and is one of the major milk and beef producing areas in the country. However, so far, no attempts at eradicating the disease have been successful. It has been suggested that the diagnostic tests used were either not sensitive or specific enough. In addition, previous studies have shown that a great number of herds are infected with Mycobacterium avium subsp. paratuberculosis (MAP). The present study estimates the effect of MAP infection under field conditions, on the diagnostic sensitivity and specificity of routine tests in live animals for Mycobacterium bovis infection diagnosis in cattle. In general, the estimations of test accuracy observed an increase in the sensitivity and specificity on MAP-infected animals for tuberculin test but observed a decrease in the sensitivity of gamma interferon tests for MAP-infected cattle. These results are different from those of previous studies considering the role of MAP infection as an interfering infection. More research is needed in order to understand the complex interactions of the different mycobacteria that can be found infecting production cattle.

Influence of vaccination against paratuberculosis on the diagnosis of caprine tuberculosis during official eradication programmes in Castilla y León (Spain)

“…This was noticed both at herd level and considering the total census of goats per farm. According to these results, it seems that PTB natural infection does not play an important role on the occurrence of false positives to the SIT test in goats (Raffo, Steuer, Monti, & Salgado, 2017;Roupie et al, 2018), unlike what may occur in other species or using other diagnostic tests (Álvarez et al, 2008;Barry et al, 2011;Seva et al, 2014). However, a fact that should be considered is that Map infection can influence the overall immune response developed in dually infected goats, compromising the sensitivity of the SIT test through an anergic effect on the cell-mediated immune response against TB infection with a decrease in the response to SIT test and subsequent occurrence of false-negative reactions (Álvarez et al, 2008;Byrne, Graham, Milne, Guelbenzu-Gonzalo, & Strain, 2019;Hope et al, 2005).…”

Is There a Relationship Between Bovine Tuberculosis (bTB) Herd Breakdown Risk and Mycobacterium avium subsp. paratuberculosis Status? An Investigation in bTB Chronically and Non-chronically Infected Herds

“…Indeed, other researchers have found during experimental co-infections that the performance of both the skin test (based on Purified Protein Derivative (PPD) tuberculin injection) and the interferon gamma test [e.g., (20, 30)] can be affected. However, the direction of effects are not always consistent across reported studies [e.g., (27, 40, 41)], but it appears that overall the current consensus is that co-infection reduces the sensitivity of tests for bTB (21), but may also negatively impact on the specificity (indeed, there is still some debate as to the dominant effect). Decreasing sensitivity of the CTT could result in more bTB false-negative animals disclosed in exposed herds, lowering the probability of truly infected herds being disclosed.…”

Development and Validation of a Novel ELISA for the Specific Detection of Antibodies against Mycobacterium avium Subspecies paratuberculosis Based on a Chimeric Polyprotein

“…However, the optimization of detection strategies that specifically identify MAP-infected animals is still crucial. One of the reasons is that the specificity of the tests available so far is severely affected in the case of exposure or infections with other mycobacteria, because of the similarity of certain antigenic components between these organisms as well as for the slow growth, difficulty of isolation, among others [ 41 – 43 ]. The development and optimization of specific and sensitive MAP detection techniques allow more efficient control strategies that will have an important impact on reducing the prevalence of PTB in herds.…”