Performance of immunohistochemistry versus real-time PCR method for detecting mycobacterial infections of cattle screened by comparative tuberculin test.

In addition to the fifty years since the test-and-slaughter program began in Iran and despite a significant reduction in the disease prevalence, positive tuberculosis cases are still being isolated from livestock farms across the country. Tests with 100% sensitivity and specificity are essential features for bovine tuberculosis diagnosis. The relationship between real-time PCR and immunohistochemistry (IHC) as two essential laboratory methods in the diagnosis of bacterial infections were aimed to evaluate single intradermal comparative tuberculin test (SICTT) results. One hundred thirty-eight cows in two groups were examined: Reactors (108 cows) and clean (as a control group; 30 cows). In the reactor group, 58(54.00%) cows were Mycobacterium bovis positive, 46(43.00%) were Mycobacterium avium subsp. paratuberculosis (MAP) positive, and 11(10.00%) were Mycobacterium tuberculosis positive. 32(55.00%) cows were co-infected with M. bovis and MAP and 5(4.55%) cows were co-infected with Mycobacterium tuberculosis and MAP in this group. Of 50 M. bovis negative cows of reactor group were 14(28.00%) MAP positive and 36(72.00%) negative, as well. Concurrent infection with all was observed in one reactor case. Comparing IHC and real-time PCR for the detection of bovine tuberculosis and Johne's disease showed very good agreement (Kappa values 0.81 - 1.00). The results also provided further confirmation on IHC and real-time PCR as a sensitive and reliable diagnostic screening approach for detection of bovine tuberculosis. The use of one laboratory method to detect bovine tuberculosis is not sufficient alone.

Pathology, immunohistochemistry and molecular study of cattle screened by comparative tuberculin test for diagnosis latent form of Johne's disease.

Mycobacterium avium subsp. paratuberculosis causes Johne's disease in cattle and other ruminants. It is one of the most widespread in terms of prevalence and one of the most important diseases in the livestock industry in terms of economic importance. In the latent form of the disease, animals can act as carriers. The main purpose of this study was to evaluate avian tuberculin in a single intradermal comparative tuberculin test (SICTT), histopathology, immunohistochemistry, and molecular methods for diagnosis of infected cows with the latent form of the disease. Twenty-three asymptomatic cows and without post-mortem signs of the disease were selected using the single intradermal comparative tuberculin test and were tested. In this study, avian tuberculin in SICTT was able to in diagnosing the latent form of the disease. The results confirm immunohistochemistry and real-time PCR as a sensitive and reliable diagnostic complementary approach for detecting latent forms of Paratuberculosis.