A COMPARISON OF GROSS PATHOLOGY, HISTOPATHOLOGY, AND MYCOBACTERIAL CULTURE FOR THE DIAGNOSIS OF TUBERCULOSIS IN ELK (CERVUS-ELAPHUS)

Using the isolation of Mycobacterium bovis as the reference standard, this study evaluated the sensitivity, specificity and kappa statistic of gross pathology (abattoir postmortem inspection), histopathology, a nd parallel or series combinations of the two for the diagnosis of tub erculosis in 430 elk and red deer. Two histopathology interpretations were evaluated: histopathology I, where the presence of lesions compat ible with tuberculosis was considered positive, and histopathology II, where lesions compatible with tuberculosis or a select group of addit ional possible diagnoses were considered positive. In the 73 animals f rom which M. bovis was isolated, gross lesions of tuberculosis were mo st often in the lung (48), the retropharyngeal lymph nodes (36), the m esenteric lymph nodes (35), and the mediastinal lymph nodes (16). Othe r mycobacterial isolates included: 11 M. paratuberculosis, 11 M. avium , and 28 rapidly growing species or M. terrae complex. The sensitivity estimates of gross pathology and histopathology I were 93% (95% confi dence limits [CL] 84,97%) and 88% [CL 77,94%], respectively, and the s pecificity of both was 89% [CL 85,92%]). The sensitivity and specifici ty of histopathology II were 89% (CL 79,95%) and 77% (CL 72,81%), resp ectively. The highest sensitivity estimates (93-95% [CL 84,98%]) were obtained by interpreting gross pathology and histopathology in paralle l (where an animal had to be positive on at least one of the two, to b e classified as combination positive). The highest specificity estimat es (94-95% [CL 91-97%]) were generated when the two tests were interpr eted in series (an animal had to be positive on both tests to be class ified as combination positive). The presence of gross or microscopic l esions showed moderate to good agreement with the isolation of M. bovi s (Kappa = 65-69%). The results show that post-mortem inspection, hist opathology and culture do not necessarily recognize the same infected animals and that the spectra of animals identified by the tests overla ps.