Indirect ELISA as a complementary diagnostic method of bovine tuberculosis

ABSTRACT: Bovine tuberculosis is an economic and health problem, requiring precise diagnostic methods for its control and eradication. The aim of this study was to evaluate the performance of a commercial enzyme-linked immunosorbent assay (ELISA) test for the diagnosis of bovine tuberculosis. A total of 1,644 cattle from eight dairy herds were evaluated using the comparative cervical tuberculin test (CCTT). Three of the herds had no recent tuberculosis infection, and the other five had shown positive results in a previous tuberculin test. For the serological diagnosis of tuberculosis, a commercial ELISA antibody test kit for Mycobacterium bovis was used. Serum samples from 846 cattle from the eight herds were evaluated using ELISA for M. bovis. Animals that were positive based on either CCTT or ELISA for M. bovis or both were sent to slaughter. Samples of their lungs, livers, and lymph nodes were collected and stored under refrigeration for microbiological culture and subsequent confirmation by polymerase chain reaction. Samples from the same tissues were also fixed with 10% formaldehyde in bottles for histopathological examination and stained with hematoxylin and eosin (HE). Of the 1,644 cattle, 61 were considered positive and 65 inconclusive based on CCTT. Retesting of the inconclusive samples identified an additional 19 positive cases, totaling 80 (4.8%) CCTT-positive animals from five herds. ELISA for M. bovis identified 4.2% (36/846) positive cattle, of which 35 were considered negative and one inconclusive based on CCTT. Of the 36 positive cases identified by ELISA for M. bovis, 27 were euthanized, 11% (3/27) showed suggestive lesions of tuberculosis on macroscopic examination, and two were confirmed by histological, microbiological, and PCR methods. The weak association of ELISA for M. bovis with the results obtained by macroscopic, histological, and microbiological isolation indicates the fragility of ELISA performance in field conditions. Therefore, it is suggested that its use as a complementary method for herd sanitation be based on the local epidemiological situation.