A presumptive diagnosis of
avian tuberculosis can be made when characteristic histologic lesions and
acid-fast bacilli are observed in avian tissue samples. However, a definitive diagnosis requires isolation and identification of the causative organism, a process that can take several weeks to complete. The purpose of the study was to determine whether
formalin-fixed,
paraffin-embedded archival avian tissues could be tested by polymerase chain reaction (PCR) to reliably and rapidly diagnose
avian tuberculosis. Tissues were examined from both presumptive and definitive cases of
avian tuberculosis from captive exotic birds obtained over a 14-yr period (1983-1997). The cases chosen consisted of birds that had characteristic histologic lesions with
acid-fast bacilli. The primers used for PCR amplified a 180-base-pair fragment of
16S ribosomal RNA, a sequence specific for both Mycobacterium avium subsp. avium and M. avium subsp.
paratuberculosis. If a sequence was detected in a sample, it was presumed that M. a. avium was the organism being detected. This M. avium fragment sequence was detected in 26 of the 97 samples (27%). Some of the negative PCR results may be explained by any of several factors that adversely affect
nucleic acid integrity, particularly prolonged fixation in
formalin. Of the 17 samples that were culture positive for M. avium and were known to have been fixed in
formalin for < or = 4 wk, 11 tested positive by PCR (65%). The findings of this study show that PCR can be a rapid
indicator of the presence of M. a. avium in
formalin-fixed,
paraffin-embedded tissues. However, the relatively low detection rate the test demonstrated in this sample set may limit its practical use as a diagnostic tool.