Submitted to: Journal of Zoo and Wildlife Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/1998
Publication Date: N/A
Interpretive Summary: A test that is used to identify the bacterium that causes tuberculosis in cattle was adapted for use in detecting the organism that causes tuberculosis in chickens. The test was then applied to tissues from captive exotic birds in a large zoological park during the years 1983-1997. All of the 97 samples examined had been collected from birds that were suspected of having tuberculosis or that had been exposed to infected birds. However, only 21 of the cases had been confirmed by bacterial culture. The test, which is based on detection of specific bacterial DNA, was successful in providing a quick and accurate diagnosis in 27 percent of the total examined. As expected, the rate was higher, 65 percent , in those instances where positive culture results had been obtained. It was also noted that the detection rate was much higher for certain types of birds, for example, 50 percent in pigeons and doves, 88 percent in ducks and geese. A very low diagnostic rate, 4 percent was observed in the traditional caged exotic birds (finch, parakeets, etc.), which suggests that tuberculosis in these birds may be caused by a different type of bacterium. Findings of this study demonstrate that although the new test is more rapid than culture for diagnosing tuberculosis in birds, the low detection rate may limit its use, especially in certain types of birds.
Technical Abstract: A presumptive diagnosis of avian tuberculosis can be made when an avian tissue has characteristic histopathologic lesions along with acid-fast bacilli. However, a definitive diagnosis requires isolation 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-embe e archival avian tissues could be tested by polymerase chain reaction (PCR) to provide a reliable and more rapid diagnosis of avian tuberculosis. Tissues were examined from both presumptive and definitive cases of avian tuberculosis from captive exotic birds covering a 14 year period. The primers used for PCR amplified a 180-bp fragment of 16SrRNA, a sequence specific for both Mycobacterium avium subspecies avium and Mycobacterium avium subspecies paratuberculosis. If a detection was made on a sample, it was presumed that M. avium subsp. avium was the organism being detected. The PCR detected the sequence in 26 of the 97 samples (27 percent). 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 samples that were culture positive for M. avium and were known to have been fixed in formalin for four weeks or less, PCR detected 11 of 17 samples (65 percent). The findings of this study demonstrate that PCR can be a rapid indicator of the presence of M. avium subsp. avium in formalin-fixed, paraffin-embedded tissues; however, the low detection rate in this sample set may limit its practical use as a diagnostic tool.