Diagnosis of paratuberculosis in naturally infected goats

A survey was carried out to verify if an immunohistochemical method associated with agar gel immunodiffusion (AGID) will establish a firm diagnosis of caprine paratuberculosis. One hundred and thirty-six goats were tested by AGID for antibodies against Mycobacterium avium subsp. paratuberculosis at two different times: the first time 22 (19.1%) were positive and the second time 25 (18%). One seronegative goat with severe diarrhea and 5 seropositive goats, two of which showing similar clinical signs, were sacrificed and necropsied. Samples were taken from small intestine, liver, spleen, mesenteric lymph nodes for bacteriological, histological and immunohistochemical examinations. M.a. paratuberculosis was isolated from intestine samples of 4 seropositive goats and from mesenteric lymph nodes of one seropositive goat; the microorganism was not isolated from samples of one seropositive and the seronegative animals. Ziehl Neelsen staining showed acid-fast bacilli in macrophages of the 5 seropositive animals and the immunohistochemical method for M. a. paratuberculosis detected bacterial antigen in the same samples.