Animal model Balamuthia mandrillaris CNS infection: Contrast and comparison in immunodeficient and immunocompetent mice: A murine model of ''granulomatous'' amebic encephalitis

Balamuthia mandrillaris and several species of Acanthanoeba are pathogenic ''opportunistic'' free-living amebas which cause granulomatous encephalitis (GAE) in humans and animals. The granulomatous component is negligible or absent, particularly in immunocompromised individuals. GAE is an ''opportunistic'' infection, usually seen in debilitated, malnourished individuals, in patients undergoing immunosuppressive therapy for organ transplants, and in Acquired Immunodeficiency Syndrome (AIDS). From around the world 156 cases of GAE have been reported from 1956 through October 1, 1995, 59 (26 in the USA) of them caused by B. mandrillaris, at least seven of them in AIDS patients. The present study was designed to compare and contrast the susceptibility of infection, the rate of infectivity and the histopathological changes within the CNS between the mutant, severe combined immunodeficient mice (SCID) infected with B. mandrillaris and the normal immunocompetent BALB-C mice. The SCID mouse is severely deficient in B and T lymphocytes, therefore lacking immunoglobulin and cell-mediated immunity. This mouse is also prone to develop early T cell lymphomas. One thousand amebic trophozoites and cysts of B. mandrillaris were intranasally and intraperitoneally inoculated in both strains of mice. Seventy percent of the intranasally inoculated SCID mice died due to CNS infection. Amebic trophozoites and cysts were found within CNS parenchyma without inflammatory response. Death occurred from 2 to 4 weeks after inoculation. By contrast only 10 percent of the intranasally inoculated BALB-C mice died with CNS infection showing the characteristic features of GAE. None of the intraperitoneally inoculated mice developed amebic infection. The SCID and BALB-C mice are logical models to study the structural alterations within the CNS of B. mandrillaris infection. This animal model recapitulates with excellent degree of fidelity several aspects of the pathogenesis and histopathological features of free-living amebic infection in human beings.