Organization of Sporulated Oocysts of Eimeria funduli in the Gulf Killifish, Fundulus grandis

Oocysts of Eimeria funduli were studied by transmission electron microscopy in naturally-infected livers of the Gulf killifish, Fundulus grandis. Tissues were cryo-processed because membranous structures in the oocyst appear to hinder routine fixation and embedment. The oocyst wall (about 25 nm thick) was adjacent to the host cell and consisted of an outer membrane that limited the host cell cytoplasm and an inner membrane separated from the outer membrane by a narrow space. In some specimens, dense material was applied to the inner face of the inner membrane. Individual sporocysts were surrounded by a membranous "veil" (about 25 nm thick) that consisted of two unit membranes. Sporopodia, projections of the sporocyst wall, supported the veil. The sporocyst wall (130-150 nm thick) consisted of two layers, a thin electron-lucent outer layer (about 10 nm thick) and a thick electron dense inner layer (about 130 nm thick). Depending on the plane of section, the inner layer had transverse striations with periods of 3 to 4 nm or 12 to 15 nm. A narrow fissure, broadest at the anterior pole of the sporocyst, extended about one-third the length of the sporocyst wall. The posterior pole of the sporocyst was characterized by a bulbous swelling. Although this swelling resembled a Stieda body in light microscopic preparations, ultrastructurally, the swelling was a knoblike thickening in the sporocyst wall and did not plug a gap in this wall

Biology and Pathogenesis of the Coccidium Eimeria funduli Infecting Killifishes

Epizootics of Eimeria funduli involved estuarine killifishes (Fundulus grandis, F. pulvereus, F. similis, and F. heteroclitus) in Mississippi, Alabama, and Virginia. All of more than 500 specimens examined of F. grandis from Mississippi during 1977 through 1979 had infections, regardless of age, sex, or season collected. Oocysts occurred primarily in the liver and pancreas, replacing up to 85% of both those organs. Infrequent sites of infection were fatty tissue of the body cavity, ovary, intestine, and caudal peduncle. Living fish did not discharge oocysts. Eimeria funduli is the first known eimerian to require a second host. To complete the life cycle, an infective stage in the grass shrimp Palaemonetes pugio had to be eaten. In 6-mo-old killifish reared in the laboratory at 24 C, young schizonts were first observed in hepatic and pancreatic cells 5 days post feeding, followed by first generation merozoites by day 10, differentiation of sexual stages during days 15 to 20, fertilization between days 19 and 26, sporoblasts from days 25 to 30, and sporozoites about day 60. Unique sporopodia developed on sporocysts by day 35 when still unsporulated. Temperatures of 7 to 10 C irreversibly halted schizogony. Both schizogony and sporogony progressed slower as age of host increased. When infective shrimp in doses ranging from 1 to 10% of a fish's body weight were eaten, the level of intensity of resulting infections did not differ significantly. Pathogenesis followed a specific sequence, with the host response apparently unable to contend with extensive infections as seen typically in nature and in our experiments. Premunition was indicated. When administered Monensin® orally, infected fish exhibited a reduction in oocysts by 50 to 70% within 20 days as compared with untreated fish. Furthermore, infected killifish maintained exclusively on a diet of TetraMin® for 3 mo completely lost their infections.

Pathogenesis of Human and Bovine Cryptosporidium parvum in Gnotobiotic Pigs

To compare the pathogenesis of human genotype 1 (HuGl) and bovine genotype 2 (BoG2) Cryptosporidium parvum, neonatal gnotobiotic pigs were given 1-10 HuGl or BoG2 oocysts. The prepatent and patent periods were significantly longer for HuGl than for BoG2 C. parvum (prepatent, 8.6 vs. 5.6 days; patent, 16.6 vs. 10.3 days). BoG2-infected pigs developed signif- icantly more severe disease than did HuGl-infected pigs. BoG2 parasites were seen micro- scopically throughout the intestines during the prepatent and patent periods. HuGl parasites were only detected during the patent period in the ileum and colon but colonized the mucosal surface in significantly larger numbers than did BoG2. Moderate-to-severe villus/mucosal attenuation with lymphoid hyperplasia was seen throughout the intestines of BoG2-infected pigs, whereas lesions in HuGl-infected pigs were mild to moderate and restricted to the ileum and colon. These findings provide additional support for the hypothesis that human and bovine C. parvum genotypes may be separate species.