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LIFE CYCLE OF CALYPTOSPORA FUNDULI (APICOMPLEXA: CALYPTOSPORIDAE)
Citation:
Fournie, J W., W. K. Vogelbein, R. M. Overstreet, AND W. E. Hawkins. LIFE CYCLE OF CALYPTOSPORA FUNDULI (APICOMPLEXA: CALYPTOSPORIDAE). JOURNAL OF PARASITOLOGY 86(3):501-505, (2000).
Description:
The taxonomic status of the extraintestinal piscine coccidium Calyptospora funduli is based in part on its requirement of an intermediate host (the daggerblade grass shrimp, Palaemonetes pugio). In this study, grass shrimp fed livers of Gulf killifish (Fundulus grandis) infected with sporulated oocysts of C. funduli exhibited numerous sporozoites suspended in the intestinal contents when examined by light microscopy of fresh squash preparations. Using this method, sporozoites were not seen in intestinal epithelial cells of the grass shrimp or in any other cell types. Ultrastructural examination, however, revealed sporozoites in the cytoplasm of the gut basal cells. Cross sections of 1 to 13 sporozoites were seen within a single cell, and those sporozoites each appeared to be situated in individual membrane-bound vesicles rather than in a single parasitophorous vacuole. These ultrastructural observations indicate that in the grass shrimp intermediate host, sporozoites which develop there into an infective stage, probably undergo that development in gut mucosal basal cells. Prior studies revealed that these sporozoites modified their structure over 4 to 5 days and that before that time they were not infective to the fish host. Following ingestion of an infected shrimp by a killifish, the infective sporozoites apparently reach the liver of their killifish definitive hosts through the bloodstream. Sporozoites were seen in blood smears from the longnose killifish, Fundulus similis, 4 hr after fish were fed experimentally infected grass shrimp. Additionally, coccidian trophozoites and early meronts were seen in hepatocytes from several longnose killifish at 48, 72, and 96 hr postinfection (PI). This study, in conjunction with previous findings, clearly confirms that a true intermediate host is required in the life cycle of C. funduli, that a developmental period of about 5 days in the grass shrimp is necessary for sporozoites to become infective to killifishes, and that sporozoites do occur intracellularly in gut basal cells of the grass shrimp. Calyptospora funduli is an apicomplexan parasite that infects a variety of atheriniform fishes along the Gulf and East coasts of North America and requires an intermediate host to complete its life cycle (Fournie and Overstreet, 1993). The role of an invertebrate intermediate host in the transmission of fish coccidia was first suggested by Landau et al. (1975), demonstrated for C. funduli by Solangi and Overstreet (1980), and postulated for some species in the genus Goussia by Overstreet (1981) and by Paterson and Desser (1982). However, the first heteroxenous life cycle to be fully demonstrated experimentally for fish coccidia was that of C. funduli in killifish (Fournie and Overstreet, 1983). They showed that excysted sporozoites in the intestine of palaemonid shrimps changed morphologically before they became infective to fishes; however, at the light microscopic level, sporozoites were not seen in host cells. Subsequently, Steinhagen and Korting (1990) confirmed that tubificid oligochaetes could serve at least as a paratenic host or vector for Goussia carpelli, and that the sporozoites were located in the cytoplasm of the intestinal epithelial cells of the oligochaete. However, Steinhagen and Korting (1988) previously showed that the oligochaete was not necessary for transmission and that direct infections could occur by fecal contamination from fish to fish. We report here details regarding the life cycle of C. funduli in its intermediate host and clarify the taxonomic status of this coccidium. Specific information is provided regarding intracellular residence of sporozoites in the alimentary tract of the grass shrimp intermediate host and the route by which these infective sporozoites reach the liver of the killifish definitive host.