الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
In the present study, 100 specimen of Pirenella conica ( family Potamidae ) , 100 of Viviparus sp. ( family Viviparidae ) ,80 of Lymnea sp. ( family, Lymneaidae ) , 50 of Valvata nilotica ( family Valvatidae ) , 100 specimen of Lanistes carinatus, ( family Pilidae ) , 50 Biomphlaria Alexandrina ( family, Thiaridae ) , 20 of Cleopatra bulimoides ( family, pleuroceridae ) , 50 of Physa acuta ( family, Physidae ) of various ages were collected from Shref Basha and Reyad Basha canals at Beni-Suef Province , 130 kilometers to the south of Cairo.Egypt Snails were transported to the laboratory, where they were isolated singly in water containers. Faeces of each snail were collected in a small dish containing approximately 2% (w\v) Potassium Dichromate.
Coccidian oocysts were proved to be found in 70 of 100 collected Pirenella conica snails , with a natural of infection of 70% . In case of Viviparus sp., the rate of infection reached only 20% (20/100) collected snails . While 75 of 100 collected Lanistes snails , with a natural rate of infection of 75% . On the other hand , there is no infection was recorded in Cleopatra sp. , Phys acuta , Biomphlaria alexandrina , Lymnea sp. and Valvata Nilotica snails. In naturally infected snails, it was observed that, Pfeifferinella sp. was transferred between hepatopancreas and small intestine of Pirenella conica snail.
The prepatent period of Pfeifferinella sp. infecting P. conica snails ranged from 14 - 18 day and the patent period was reached 50 days ( p.i. ). Merogony stages were the early stages observed in this study. These stages were concentrated in the hepatopancreas and were found in a large clear parasiteophorous vacuole ( PV ) and were observed as early as 3 days after infection ( p.i. ). They measured 9.4 x 7.2 urn, in snails killed 5 days ( p.i. ) immature meronts were measured 12 x 10 um containing 8 nuclei. Meanwhile, mature meronts with about 6 differentiated merozoites were detected as early as 7 days ( p.i. ). Merozoites have a pointed anterior end and a rounded posterior one with a nucleus near the center. These merozoites measured 3.1 x 1.4 um.
Throughout electron microscopy banana shaped sprozoites converted to spherical shaped young uninucleated meronts. These meronts contain centrally located large spherical nucleus and double layered pellicle. Merogony started by division of this centrally located nucleus giving rise many nuclei arranged at the periphery of the multinucleated meronts. With maturation a rosette shaped meront with developed merozoites were formed.
The earliest gametogonic stages were seen in the intestine of Pirenella conica snails killed 10 days post-infection. Microgamonts containing about 4 nuclei and measured 7.9 x 6.7 um. Macrogamonts were oval in shape with a single nucleus and the cytoplasm was characterized by the presence of dark structures known as wall forming bodies. And observed at 12 day ( p.i. ) in a parasitophorous vacuole. The macrogamonts measured 7.3 x 5.6 um. Macrogametes were characterized by the presence of the so called vaginal tube. Fertilization was occurred in the intestine of the infected snails at 12 day (p.i.). Zygotes developed into young oocysts after fertilization.
By electron microscope microgametogenesis started by banana shaped merozoites converted to spherical shaped young uninucleated microgamont. This microgamont contains centrally located large spherical nucleus and double layered pellicle. The centrally located nucleus divided producing many nuclei arranged at the periphery of the multinucleated microgamont. With maturation microgametes formed in a large number from the mature microgametes. On the other hand macrogametogenesis started by formation of vaginal tube, this tube was curved in shap, with tapered end. The wall of vaginal tube was thin and was higly osmiophilic, developed at the antirostral pole of the macrogametes, this tube measured 4.3 x 1.1 um.
Sporogony occurred in the tissues of the host cell as indicated by the presence of fully sporulated oocysts in stained sections of intestine. In the earliest stage, the nucleus of young oocyst was occupied the central position that were observed through the examination of the intestine of infected Pirenella snails at 14 day post-inoculation. These oocysts were found to be colourless and ellipsoid or spherical in shape measured 9.5 x 8 um. The oocyst wall consists of two layers : an outer light and thick layer (~ 0.6 um ) , an inner dark and thin layer which difficult to measure micropyle and micropyle cap were not observed in these oocysts, wall formig bodies type one ( WFB ) were arranged at the periphery of oocyst directly under the developed oocyst wall.
In the first event of sporulation, the nucleus of the oocyst divided into two nuclei. Later on, two divisions occurred and the oocyst became containing 8 nuclei distributed randomly within its cytoplasm. As development proceeded, each nucleus incorporated a part of the cytoplasm forming 8 sporozoites filling the entire cavity of the oocyst without sporocyst formation. Fully sporulated oocysts were excreted in the faces of infected snails from 14 - 18 day ( p.i. ), these oocysts measured 9.5 x 8.5 um. Micropyle was absent, while a residual body was observed.