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

Abstract

Ocular, peroral, intraperitoneal, intramuscular, and subcutaneous inoculation of severe combined immunodeficient (SCID) mice with spores of the human isolate (CDC: V404) of Brachiola algerae (syn. Nosema algerae) (Phylum Microspora) revealed that the microsporidium develops in viscera of the immunodeficient mouse host, but only after the ocular administration of spores. It is hypothesized that the physico-chemical milieu of the conjunctiva and cornea 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 site. However, severe infection in the liver was found 60 days after infection, manifested as hepatosplenomegaly and multifocal miliary necroses and granulomas containing parasites. No microsporidia were found in any other tissues. Transmission electron microscopy revealed characteristic tubulovesicular ‘secretory materials’ on the plasma membrane of all developmental stages of B. algerae except sporoblasts and spores. These formations increase the parasite surface and allow more efficient metabolic communication of the parasite with the host cell. It is hypothesized that the presence of these structures is a factor helping the parasite to grow in a variety of hosts and tissues. Ultrastructural characters support the likelihood that B. algerae and B. vesicularum are conspecific, and that there exists a relationship between species of the genera Brachiola and Anncaliia.