Progressive disseminated infection with Mycobacterium avium complex after intravenous and oral challenge in cyclosporine-treated rats.

Male Sprague-Dawley rats, immunosuppressed with cyclosporine (CsA), developed disseminated infection after intravenous or oral challenge with Mycobacterium avium complex (MAC). Disseminated infection leading to bacillemia could be established after intravenous inoculation with as few as 5 x 10(3) organisms. When CsA was not given or when CsA was stopped 1 month after infection, animals cleared the bacilli from blood and tissue. Animals developed disseminated infection after oral challenge with as few as 10(6) organisms. Persistent bacillemia occurred when organisms in the spleen exceeded 10(7). Differences in virulence among strains were observed. Infected tissues showed histopathologic changes similar to those seen in patients with AIDS. The CsA-treated rat is a new model that appears useful for studies of the virulence of MAC strains and the pathogenesis of disseminated MAC infection.