SEROCONVERSION CAN PRECEDE CULTURE CONFIRMED DIAGNOSIS OF MYCOBACTERIUM TUBERCULOSIS INFECTION IN ASIAN ELEPHANTS (ELEPHAS MAXIMUS) BY DECADES

Mycobacterium tuberculosis (M. tb) infection was diagnosed in 16 human-managed Asian elephants (Elephas maximus) at four different US facilities. A retrospective review was performed to collate information on serological test results and describe the timelines from exposure to an elephant known to be positive for M. tb, detection of antimycobacterial antibodies in the exposed elephant, and M. tb isolation from the exposed elephant to confirm diagnosis. Seroconversion was defined by a positive test result using ElephantTB STAT-PAK, multiantigen print immunoassay, or DPP VetTB assay for elephants (Chembio Diagnostic Systems, Inc). Fifteen elephants were adults (age ≥24 yr) at first seroconversion and 26 yr or older when confirmed by a positive M. tb culture. Six animals were diagnosed postmortem, and 10 were diagnosed antemortem by positive trunk wash (TW) culture. The interval between last known exposure to an M. tb–positive elephant and serological conversion was 8.5 yr (median; range 0–18 yr) in the eight animals that had not already seroconverted. The median time from seroconversion to isolation of M. tb was 2.8 yr in elephants diagnosed by TW culture (antemortem) compared with those diagnosed postmortem (median 1.2 yr). Of the 10 elephants diagnosed antemortem, four were seropositive for 14 or more yr (range 0–33 yr) prior to the M. tb–positive culture. The median number of negative TW samples submitted between seroconversion and diagnosis by culture was 16 (range 0–151 samples). In contrast, a median of 48 negative TW cultures and 10 yr elapsed (range 0–41 yr) between exposure and culture diagnosis. Although this descriptive report has limitations, these findings are useful for veterinarians faced with an M. tb–seropositive elephant. This report supports the recommendation of increasing TW surveillance if an elephant has a history of exposure to an M. tb–positive elephant and has multiple seropositive results.