Early lesions following aerosol infection of rhesus macaques (Macaca mulatta) with Mycobacterium tuberculosis strain H37RV.

As part of a study to investigate early changes following exposure to aerosols of Mycobacterium tuberculosis (Mtb), 10 rhesus macaques (Macaca mulatta) were infected with high (731 colony forming units [cfu]), medium (70 cfu) or low (7 cfu) doses of Mtb, and tissues were examined at 2 and 3 weeks post infection (wpi). Clinical disease was not observed. Results of advanced imaging and pathological findings were compared with respect to the delivered dose and time post infection. Magnetic resonance imaging revealed lesions in the lungs at these early time points ex vivo immediately prior to detailed post-mortem examination in the absence of clinical disease. In animals exposed to high and medium doses of Mtb that were studied at 2 and 3 wpi, a range of lesions including small foci of mainly mononuclear cells, primarily macrophages (granulomatous lesions), as well as obvious granulomas, were observed microscopically in the lungs, including lymphatics and hilar lymph nodes. In the low-dose group at 3 weeks, small lesions were identified in the lung and hilar lymph nodes of one animal, and the remaining two animals in this group had lesions in either lung or hilar lymph node. Acid fast bacilli were demonstrated in the lung and lymph nodes in all animals that received high and medium doses, and the lymph nodes of two animals at the low dose. A dose-dependent effect was observed with increasing dose and time post infection. Furthermore, early dissemination of bacilli to the draining, hilar lymph nodes with concomitant granulomatous lesion formation was observed. By contributing to the recognition of early lesion development due to aerosol challenge of Mtb in the rhesus macaque, this study forms a basis for further investigation of early lesions and may inform the design of future vaccine and therapeutic studies involving early time points in this species.