Sensitivity, specificity, and confounding factors of novel serological tests used for the rapid diagnosis of bovine tuberculosis in farmed red deer (Cervus elaphus)

Abstract

In this study, novel serological tests were used to detect tuberculosis (TB) in groups of farmed red deer (Cervus elaphus) varying in disease status or possible confounding factors. Groups of deer naturally or experimentally infected with Mycobacterium bovis and animals vaccinated against paratuberculosis were studied, as were uninfected animals and animals naturally or experimentally infected with Mycobacterium avium subsp. paratuberculosis. Sera were assayed using two rapid lateral-flow tests, Chembio's CervidTB STAT-PAK and DPP VetTB tests, and results were compared to those from tuberculin skin tests. Both serological tests had a high sensitivity, but specificity was adversely affected after animals had received a vaccine against paratuberculosis and were subsequently skin tested. The specificity of the DPP VetTB test was higher than that of the CervidTB STAT-PAK test, with natural infection with M. avium subsp. paratuberculosis adversely affecting the specificity of only the CervidTB STAT-PAK test. The sera from M. avium subsp. paratuberculosis-infected deer that produced false-positive reactions in the CervidTB STAT-PAK test were retested with a multiantigen print immunoassay (MAPIA), and some of these sera were shown to react with the MPB83 antigen. Combining the results from the serological tests and the skin tests showed only a slight increase in the sensitivity of detection of M. bovis-infected animals. It is concluded that both the CervidTB STAT-PAK and DPP VetTB tests offer rapid, convenient, and easy detection of bovine tuberculosis in deer, albeit with significant interference from paratuberculosis vaccination status and subsequent skin testing. The latter finding illustrates one of the limitations of currently available vaccines against paratuberculosis.

FIG. 1.

MAPIA of 10 Mycobacterium bovis proteins or fusion proteins plus bovine PPD (B-PPD) and M. bovis culture filtrate (MBCF), performed using sera from 10 TB-free deer which had been experimentally infected with Mycobacterium avium subsp. paratuberculosis. All of these sera had previously reacted false positively in the CervidTB STAT-PAK test.