Glycolipid antigen for use in diagnostic assays for bovine tuberculosis

Use of recombinant proteins in antibody tests for bovine tuberculosis

Tuberculosis (TB) in cattle remains a major zoonotic and economic problem in many countries. Since the standard diagnostic assay, the intradermal test (IDT) with bovine PPD tuberculin, has less than optimal accuracy in all situations, other diagnostic methods such as serological assays have been investigated. Because of fundamental concerns for the low sensitivity and specificity of previous ELISA protocols, a profiling ELISA with nine purified, recombinant proteins of TB complex mycobacteria, was employed on samples from four groups of cattle: (a) naturally Mycobacterium avium-exposed and experimentally Mycobacterium bovis-infected, (b) officially-certified TB-free herds, (c) exposed to M. bovis in two field TB outbreaks and scored as bovine reactors in the gamma-IFN assay for bovine TB, (d) paratuberculosis (para TB)-infected. The described ELISA proved to be highly specific. In fact, the antibody (Ab) response could be consistently detected in 3 out of 3 endotracheally-infected calves and in 1 out of 3 contact-infected calves. There was also a very low prevalence of low-titered, non-specific Ab responses in paraTB-infected animals. As for the animals exposed to field TB outbreaks, 16 out of 28 gamma-IFN positive cattle were also Ab-positive; importantly, 7 out of 12 gamma-IFN positive, IDT-negative cattle showed Ab responses to TB proteins. In general, the profile of the Ab response varied among animals; the reaction to single recombinant antigens was sometimes transient and fluctuating, whereas the panel of antigens on the whole was indeed more effective in Ab detection.

BOVIGAM: an in vitro cellular diagnostic test for bovine tuberculosis

BOVIGAM which is based on the detection of gamma interferon (IFN- gamma) is a rapid, laboratory assay of a cell mediated immune response that may be used for the detection of tuberculosis (TB) infection in animals. Whole blood is first incubated overnight with bovine PPD, avian PPD or negative control antigens, and IFN- gamma in the supernatant plasma is then measured by EIA. TB infection is indicated by a predominant IFN- gamma response to bovine PPD. Since 1988, BOVIGAM has been extensively trialed on more than 200 000 cattle in Australia, Brazil, Ireland, Northern Ireland, Italy, New Zealand, Romania, Spain and the USA. Sensitivity has varied between 81.8% and 100% for culture-confirmed bovine TB and specificity between 94% and 100%. The IFN- gamma assay detects M. bovis infection earlier than the skin test and in New Zealand is applied to detect skin-test negative cattle with TB, where after slaughter a significant number of IFN- gamma reactors have TB. BOVIGAM is also approved in New Zealand for serial testing skin test positive cattle when non-specificity is suspected. Cattle are tested 7-30 days after a positive caudal fold test. The boosting effect of the skin test on T-cell activity allows blood to be cultured with PPD up to 30 h after collection without effecting accuracy. The BOVIGAM results are not affected by poor nutritional condition and are only mildly and briefly affected by dexamethasone treatment and parturition. IFN- gamma responses of cattle vaccinated with BCG are dose-dependent and short-lived. The BOVIGAM kit is now used routinely in many countries for the detection of M. bovis infected cattle, buffalo and goats.