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  • Blackwell Publishing Ltd  (2)
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  • 1
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: . Mature gamonts of Haemogregarina magna lie within a type of parasitophorous vacuole (Pv) apparently unique to the haemogregarines. The cytoplasm of infected erythrocytes was separated from the parasite by two Pv membranes. An additional membrane, coated on both sides with electron-dense material, closely invested the gamonts. The apical complex of the gamonts includes a conoid, two preconoidal rings, and an elaborate polar ring complex. The latter consisted of the polar ring and approximately 78 posteriorly directed, radially arranged, “tine-like” structures which fuse as they merge anteriorly into the polar ring. Freeze fracture replicas demonstrated that the pellicle of gamonts of H. magna was structurally similar to that of other apicomplexans. The closely apposed inner membranes of the pellicle formed plates which were arranged into strips along the long axis of the gamont. Calculations indicated that 13 such strips are found around the circumference of the gamonts with about six subpellicular microtubules associated with the inner surface of each strip. Gamonts of H. magna share many structural similarities with the kinetes, ookinetes, and sporokinetes of other apicomplexans. We propose that the conoid and polar ring complex are fundamental features of all apicomplexan “kinetes.”
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The sporogonic and merogonic development of Babesiosoma stableri Schmittner & McGhee, 1961 within its definitive host and vector, a leech Batracobdella picta (Verrill, 1872), was studied by light and electron microscopy. Gamonts released from frog erythrocytes in the blood meal of the leech associated in syzygy and fused; the gamonts were isogamous and only 1 microgamete was formed. The ultrastructural appearance of the resulting zygote was similar to that of the gamonts, but it was larger. The zygote had an apical complex (including a polar ring, conoid and 2 pre-conoidal rings and micronemes, but no recognizable rhoptries), triple-membraned pellicle, about 40 subpellicular microtubules and prominent stores of amylopectin. Zygotes penetrated the cells of the intestine and underwent sporogony directly within the cytosplasm of the ieech epithelial cell without the formation of a parasitophorous vacuole. Eight sporozoites budded simultaneously around the periphery of an irregularly shaped oocyst. No oocyst wall was formed. Each sporozoite had a complete apical complex (including rhoptries), abundant amylopectin inclusions and a triple-membraned pellicle with about 32 subpellicular microtubules. The sporozoites initiated merogonic replication primarily within the salivary cells of the leech although other tissues, such as muscle, were infected. Each meront produced 4 merozoites by simultaneous budding, forming a cruciform meront typical of the intraerythrocytic development of this parasite. The meront was located directly within the cytoplasm of the host cell. Merozoites, with abundant amylopectin, had a complete apical complex and triple-membraned pellicle with about 40 subpellicular microtubules. The merozoites either initiated a further cycle of replication, or they moved into the ductules of the leech salivary cells which extend to the tip of the proboscis. Observations on gametogenesis. syngamy and sporogony of B. stableri in its leech host indicate that the family Dactylosomatidae should be placed in the suborder Adeleina (Eucoccidiida: Apicomplexa). Babesiosoma stableri was transmitted to uninfected frogs (Rana spp.) by the bite of infected leeches. Prepatent periods ranged from 26 to 38 days at 25° C. Despite a directed search in laboratory reared tadpoles which had each been injected intraperitoneally with 150,000 merozoites, no pre-erythrocytic developmental stages were observed. Similarities in their biology suggest close phylogenetic affinities of the dactylosomatids, and other adeleid blood parasites, with the piroplasms of higher vertebrates.
    Type of Medium: Electronic Resource
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