The human isolate of Brachiola algerae (Phylum Microspora): development inSCID mice and description of its fine structure features

Ocular, peroral, intraperitoneal, intramuscular, and subcutaneous inoculati on of severe combined immunodeficient (SCID) mice with spores of the human isolate (CDC: V404) of Brachiola algerae (syn. Nosema algerae) (Phylum Micr ospora) revealed that the microsporidium develops in viscera of the immunod eficient mouse host, but only after the ocular administration of spores. It is hypothesized that the physico-chemical milieu of the conjunctiva and co rnea helped to adapt the originally 'poikilothermic microsporidian' to the conditions within the homoiothermic organism. Ocular application of spores caused no clinical signs of disease at the application situ. However, sever e infection in the liver was found 60 days after infection, manifested as h epatosplenomegaly and multifocal miliary necroses and granulomas containing parasites. No microsporidia were found in any other tissues. Transmission electron microscopy revealed characteristic tubulovesicular 'secretory mate rials' on the plasma membrane of all developmental stages of B. algerae exc ept sporoblasts and spores. These formations increase the parasite surface and allow more efficient metabolic communication of the parasite with the h ost cell. It is hypothesized that the presence of these structures is a fac tor helping the parasite to grow in a variety of hosts and tissues. Ultrast ructural characters support the likelihood that B. algerae and B. vesicular um are conspecific, and that there exists a relationship between species of the genera Brachiola and Anncaliia.