A modification of a highly practical human interferon-gamma release assay for the diagnosis of tuberculosis (TB), the QuantiFERON((R))-TB Gold (In-Tube Method) (QFG-IT) assay, was evaluated for diagnosing natural mycobacterial infection in rhesus macaques (Macaca mulatta). All animals in a captive colony were tested using the QFG-IT and tuberculin skin test (TST). Animals testing positive to these tests were euthanised and necropsied. Selected tissues were processed for histopathology and mycobacterial culture, and positive cultures were speciated by Mycobacterium tuberculosis complex polymerase chain reaction (PCR) and 16S rRNA gene PCR sequencing techniques. M. tuberculosis was cultured from a TST-positive/QFG-IT-positive animal which showed gross pulmonary pathology typical of TB. Additionally, Mycobacterium kansasii was cultured from a TST-negative/QFG-IT-positive animal which had no pathological or histopathological signs of mycobacterial infection. The detection of M. kansasii infection in a QFG-IT-positive animal which showed no evidence of disease indicates that this test might be a highly sensitive tool for the diagnosis of mycobacterial infection in rhesus macaques. However, these findings highlight the limitations of the QFG-IT to specifically detect infection by the pathogens M. tuberculosis and Mycobacterium bovis.
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