Evaluation of an agar gel immunodiffusion test kit for detection of antibodies to Mycobacterium paratuberculosis in sheep

Abstract

Objective - To determine whether a commercially available agar gel immunodiffusion test approved for detecting antibodies to Mycobacterium paratuberculosis in cattle could be used for sheep. Design - Experimental trial. Sample Population - Serum samples from 27 sheep confirmed to have paratuberculosis by means of acid-fast staining of smears of ileal mucosa, histologic examination of tissues, or bacteriologic culture; 7 sheep with clinical signs of paratuberculosis; and 55 sheep from 5 uninfected flocks. Procedure - Serum samples were tested concurrently with the commercially available test and with a previously validated agar gel immunodiffusion test. Multiple samples collected from 13 infected sheep over a period of 6 years were also tested so that each test's ability to detect onset of seroposittvity could be compared. Results - For both tests, results for samples from all 55 uninfected sheep were negative, results for samples from 32 of the 34 sheep with paratuberculosis were positive, and results for the remaining 2 sheep with paratuberculosis were negative. Results of both tests were in agreement for 50 of 54 samples obtained from 13 infected sheep over time. The 4 samples for which results of the 2 tests disagreed were the fourth, eighth, and ninth of 10 samples from 1 sheep and the first of 6 samples from a second sheep. For all 4 samples, the commercially available assay yielded a weak-positive result, but the previously described test yielded a negative result. Clinical Implications - The commercially available agar gel immunodiffusion test approved for use in cattle may be useful in the differential diagnosis of paratuberculosis in sheep.