Comparative Evaluation of Indirect-Elisaand IS900 PCR Assay for Diagnosis of Ovine Johne's Disease

Ovine Johne's disease (OJD) is caused by Mycobacterium avium sub sp. paratuberculosis (MAP). The disease presents diverse bacteriological, immunological and pathological spectra leading to variable efficacies of diagnostic methods at different times during the course of infection. The study was carried out to evaluate the sensitivity and specificity of indirect-enzymelinked immunosorbent assay (ELISA) using IS900 faecal polymerase chain reaction (PCR) assay as gold standard. A total of 100 clinical samples, serum (n = 50) and faeces (n = 50), were collected from 50 adult Bannur sheep from Livestock Research and Information Centre farm Nagamangala, Mandya district of Karnataka. Of 100 total samples, 23 (23%) serum and 44 (44%) faecal samples were positive by indirect-ELISA and IS900 PCR assay, respectively. The sensitivity and specificity of indirect-ELISA compared with IS900 PCR assay was 50% and 98.21%, respectively. Kappa and area under curve value indicates moderate agreement between indirect-ELISA and IS900 faecal PCR assay. The present study indicated that IS900 faecal PCR was more sensitive and specific test than indirect-ELISA in detecting for MAP infection and for early diagnosis of JD in sheep. Indirect-ELISA was screening test and IS900 PCR assay was an individual confirmatory test. Combination of indirect-ELISA with IS900 faecal PCR assay may be adopted as a model strategy for screening and diagnosis of JD in sheep.