Invasion of the brain and chronic central nervous system infection after systemic Mycobacterium avium complex infection in mice

Central nervous system (CNS) infections caused by nontuberculous mycobacter ia have been described previously, especially in patients with AIDS. To inv estigate specific aspects of the pathogenesis of this entity, C57BL bg(+)/b g(-) mice were infected intravenously with Mycobacterium avium, and culture s of blood and brain as well as histopathology examination of brain tissue were carried out at several time points up to 6 months after infection. Low -grade inflammatory changes with small aggregates of lymphocytes and macrop hages as well as perivascular cuffing were seen early in the infection. A s mall number of bacteria could be observed in the parenchyma of the choroid plexus. Six months after infection, numerous bacteria were present within t he foamy macrophage of the granulomatous lesions along the ventricle and me ninges. None of the mice developed clinical signs of meningitis or encephal itis or even died spontaneously during the period of observation. Use of CD 18(-/-) knockout mice indicated that transport of the bacterium within neut rophils or monocytes into the brain is unlikely. Mild chronic CNS infection developed in the mice during sustained systemic M. avium infection, simila r to what has been reported in most human cases.