Experimental infection of calves with an apparently specific goat-pathogenic strain of Mycobacterium paratuberculosis

Four calves and four goat kids were inoculated perorally with a Norwegian goat-pathogenic strain of Mycobacterium paratuberculosis. None of the calves developed clinical disease, pathological lesions or humoral antibody response, but the organism was reisolated from the small intestine and mesenteric lymph nodes when the calves were slaughtered after 7, 12, 14 and 18 months, respectively. As one of the goats died of non-specific causes and one did not become infected, two remained as positive controls. One of these became subclinically and one clinically infected, but both showed distinct histopathological lesions at necropsy. Both were shown to be positive in the complement fixation test (CFT) and the enzyme-linked immunosorbent assay (ELISA) but only the clinically affected goat proved positive in the agar gel immunodiffusion (AGID) test. The AGID test was found to be of low diagnostic value, and the ELISA was as sensitive as the CFT in detecting infection at an early stage. However, when infection was finally established, the ELISA titres became far higher than the CFT titres. The results confirm previous experience in Norway, that the current Norwegian strain of M. paratuberculosis has little or no pathogenicity for cattle.