Serum based screening and molecular detection of brucellosis in ruminants

Brucellosis is a highly infectious bacterial disease that mainly affects cattle, sheep, pigs, goats, dogs, horses and wild animals primarily caused by Brucella abortus, B. ovis, B. suis, B. melitensis, and B. canis. It has a significant threat to the livestock and human community mainly in developing countries and requires accurate diagnosis, characterization and management. This study was undertaken in 238 samples (112 serum samples from the sheep, 82 serum samples from the goat and 44 serum samples from the cattle) suspected of brucellosis collected from the southern districts of Tamil Nadu. All the 238 samples were screened for the brucellosis by carrying out rose bengal plate agglutination test (RBPT). The seropositive serum samples were further subjected to Brucella cell surface salt extractable protein 31 (BCSP 31) gene-based PCR for Brucella genus confirmation. The BCSP 31-PCR positive samples were further subjected to Brucella-AMOS (avis-melitensis-ovis-suis) multiplex PCR for identification of B. abortus, B. ovis, B. melitensis and B. suis species. The study revealed that 8.92% (n = 10) serum samples from sheep, 9.75% (n = 8) serum samples from goat and 6.81% (n = 3) serum samples from cattle were seropositive for brucellosis by RBPT. All the twenty one seropositive samples produced specific amplicon of 223 bp by BCSP 31-PCR confirms brucellosis. Further molecular typing of BCSP 31-PCR positive samples by Brucella –AMOS PCR revealed specific amplicon of 498 bp indicating the involvement of B. abortus in 19 serum (10 from sheep, 6 from goat and 3 from cattle) samples. One serum sample from goat revealed specific amplicons of 498 bp and 731 bp indicating the involvement of both B. abortus and B. meletensis. Another serum sample from goat yielded specific amplicons of 498 bp, 731 bp and 285 bp suggesting the mixed infection of B. abortus, B. meletensis and B. suis, respectively. The B. abortus is the common species involved in cattle, sheep and goat infections. Two caprine samples showed mixed infection which involves B. abortus, B. meletensis and B. suis species. The study concludes that the serum can be used as an alternate specimen for the fast and reliable molecular diagnosis of brucellosis.