Experimental meningoencephalomyelitis by Encephalitozoon cuniculi in cyclophosphamide-immunosuppressed mice.

Encephalitozoonosis is an increasingly important opportunistic protozoan infection in immunocompromised individuals. This study aims to examine the development of an experimental Encephalitozoon cuniculi infection in the central nervous system of immunosuppressed mice. Adult Balb-C mice were inoculated intraperitoneally with E. cuniculi spores, treated with cyclophosphamide during the experimental period and killed from 15 to 75 days post-inoculation. Tissue samples were collected and processed for light and transmission electron microscopy investigation. Multifocal granulomas were seen in all organs. A lymphocytic, diffuse, non-suppurative menigoencephalomyelitis was observed, with neuronal degeneration and necrosis, macrophagic infiltration and reactive astrocytosis. E. cuniculi spores were seen in the microgranulomas or occurred unassociated with inflammatory reaction. The parasites were rarely seen in Hematoxylin-Eosin stained sections, but were Gram-Chromotrope positive. Proliferative forms and spores were found in parasitophorous vacuoles within neural cells and macrophages. Experimental encephalitozoonosis in immunosuppressed mice provides an useful model for the study of brain lesions associated with these protozoans in man.