Submitted to: Parasitology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2003
Publication Date: 4/4/2005
Citation: Elsheika, H.M., Mansfield, L.S., Fitzgerald, S.D., Rosenthal, B.M., Saeed, M.A. 2005. Dexamethasone treatment induces susceptibility of outbred webster mice to experimental infection with besnoitia darlingi isolated from opossums (didelphis virginiana).. Parasitology Research 20:128-131. Interpretive Summary: Opossums have recently been implicated as definitive hosts for Sarcocystis neurona, the causative agent of Equine Protozoal Myeloencephalitis, a debilitating neurological condition of horses and other infected host species. Opossums also are vulnerable to tissue cyst infections with related parasites belonging to the genus Besnoitia. Here, two isolates of Besnoitia darlingi are described in clinical, ultrastructural, and genetic terms; an animal model of infection employing immune-suppressed outbred mice is presented for the fist time; and cell cultures are established that facilitate the long-term study of this poorly characterized parasite species.
Technical Abstract: Few experimental models are available for studying a diverse assemblage of tissue cyst-forming coccidian parasites, including members of the genus Besnoitia. Here, we describe how suppression of cellular immunity rendered outbread mice susceptible to two isolates of Besnoitia darlingi originating in naturally infected opussums, and the subsequent development of long-term tissue cultures that maintained viable parasites. Numerous cysts typical of parasites belonging to the Apicomplexan genus Besnoitia were found in lungs, liver, kidneys, spleen, heart, tongue, diaphragm, abdominal muscles, skin, and ears of the opossums. The light microscopic and ultrastructural characteristics of the cysts and bradyzoites were consistent with that of Besnoitia darlingi, and this diagnosis was also supported based on comparative sequence analysis at each of two genetic loci. Bradyzoites recovered from crushed cysts from the infected opossums were inoculated into outbred Webster laboratory mice by intraperitoneal and subcutaneous routes. The tachyzoites induced severe systemic infection in mice treated with dexamethasone, but were not pathogenic to mice treated with sulfadiazine. Isolates recovered from the inoculated mice were viable and could be maintained in long-term tissue cultures.