An evaluation of an anamnestic ELISA for the detection of tuberculous cattle

An ELISA, that used bovine PPD or MPB 70 as test antigen, was evaluated for its ability to detect cattle with macroscopic tuberculous lesions, that were not identified by the Single Intradermal Comparative Tuberculin Test (SICTT). A serum sample was collected seven to 14 days after the SICTT from each of 1,522 cattle which had passed the skin test. These cattle were located in 47 herds about to undergo complete depopulation because of a history of chronic infection or an extensive tuberculosis breakdown. All SICTT-negative cattle were subjected to detailed post-mortem examination within seven days of blood sampling. Tuberculous lesions were detected in 32 of these animals, all of which yielded Mycobacterium bovis on culture. Two animals had generalised tuberculosis; sera from these animals gave significantly higher OD values in the ELISA tests than did sera from the 30 animals in which the lesions were restricted to a small number of lymph nodes. Overall, the sensitivity of the ELISA in identifying infected animals was 31% for the MPB70 antigen at OD threshold of 0.2 and 9% for the bovine PPD antigen at OD threshold of 0.39. The results suggest that an ELISA that uses Bovine PPD or MPB70 as antigen might be useful to identify SICTT-negative cattle that have generalised tuberculosis.