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

Abstract

Male Sprague-Dawley rats, immunosuppressed with cyclosporine (CsA), developed dissemi-nated 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 103 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 dissemi-nated infection after oral challenge with as few as 106 organisms. Persistent bacillemia occurred when organisms in the spleen exceeded 107 • Differences in virulence among strains were ob-served. 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. Disseminated Mycobacterium avium complex (MAC) in-fection is the most common cause of bacillemia in patients with AIDS, where it may be diagnosed in up to 50 % of pa-tients [1]. The impact of MAC infections on morbidity and mortality in this population has grown as improvements i