Mycobacterium kansasii in a rhesus monkey.

The incidence of pulmonary disease caused by "atypical" mycobacteria has been increasing gradually in the human population since the 1950s. Mycobacterium kansasii and Mycobacterium intracellulare are the two organisms most responsible for this trend. A rhesus monkey was euthanatized and necropsied after reacting positive to mammalian Old Tuberculin on semi-annual testing. Histopathology demonstrated the presence of small numbers of acid fast organisms in pulmonary lesions. Further microbiological testing identified the causative organism as M. kansasii.