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  • 1
    Electronic Resource
    Electronic Resource
    Stable Patterns of Allelic Diversity at the Merozoite Surface Protein-1 Locus of Plasmodium falciparum in Clinical Isolates from Southern Vietnam (1998)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 45 (1998), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The extent of allelic diversity at the Merozoite Surface Protein-1 locus of Plasmodium falciparum (PfMSP-1) was examined in isolates collected from symptomatic patients living in a mesoendemic area in southern Vietnam. The variable blocks 2, 4 and 10 were typed by polymerase chain reaction and 24 PfMSP-1 gene types were defined as unique combinations of allelic types detected in each variable block. Nineteen PfMSP-1 gene types were identified and 182 parasite populations were fully typed among 102 isolates. Forty-eight (47%) patients harbored more than one typed parasite population, and one patient had at least eight genetically distinct subpopulations. As previously shown in the same endemic area, recombination between blocks 4 and 10 was significantly less frequent than expected from random assortment of allelic types. The distribution of PfMSP-1 gene types, however, did not differ significantly from that observed in isolates collected in the same area 17-24 mo before the present study. Furthermore, the prevalence of the most common gene types and the average number of different gene types harbored by the same host did not decrease with age. This argues against the prominence of frequency-dependent immune selection of PfMSP-1 polymorphisms in this parasite population.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1998.tb05080.x
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  • 2
    Electronic Resource
    Electronic Resource
    Development of Plasmodium berghei Ookinetes to Young Oocysts In Vitro (1992)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 39 (1992), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: . The mosquito stage of Plasmodium berghei was cultivated in vitro, with special attention to ookinete transformation into early oocyst. The ookinetes were obtained by in vitro culture of gametocytes taken from infected mice, purified by density gradient of metrizoic acid or a lymphocyte separation medium, and incubated either in acellular culture or in co-cultivations with mosquito cells. In acellular culture, the ookinetes were found to aggregate with each other and transformed from banana to round shapes. Their inner pellicular membranes and subpellicular microtubules partially disappeared, indicating that development to early oocyst had occurred. Co-cultivation with Aedes albopictus cells (C6/36 clone) revealed that ookinetes transformed into early oocyst in the medium, or invaded the cells and then transformed to early oocysts within the cell cytoplasm as well. However, all of these transformed cells failed to develop further, i.e. neither deposition of the oocyst capsule nor nuclear division was observed. Many ookinetes which failed to penetrate the Aedes cells were phagocytized within three days of culture. A significant difference between invaded and transformed oocysts and phagocytized ookinetes was seen in that the former lacked vacuole membrane. Co-cultivation with Toxorhynchites amboinensis cells (TRA-284-SFG clone) permitted transformation of ookinetes into early oocysts in the medium as in the acellular culture, but no ookinete invasion nor phagocytosis by the cell was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1992.tb01325.x
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  • 3
    Electronic Resource
    Electronic Resource
    Gamete development inPlasmodium berghei regulated by ionic exchange mechanisms (1992)
    Springer
    Parasitology research 78 (1992), S. 277-284 
    Details
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Ionic regulation in the induction of exflagellation ofPlasmodium berghei was investigated by culturing the parasites in various isotonic media. Of the salts tested, NaHCO3 exhibited the highest activity in inducing exflagellation, whereas KHCO3 showed no activity. In the absence of HCO 3 − , media containing monovalent cation (Na+, K+, Cs+, Rd+, choline+, lysine+, arginine+) and Cl− also induced exflagellation, but their activities were lower than that of NaHCO3. Anions of Br− or NO 3 − could be substituted with Cl−, whereas other anions such as I−, NO 2 − , SO 4 2− , SCN−, H2PO 4 − , or HPO 4 2− failed to induce exflagellation, as did tetramethylammonium-Cl, CaCl2, MgSO4, MgCl2 and sucrose as well. These results suggest that the induction of exflagellation requires the presence of Na+ and HCO 3 − or monovalent, membrane-permeable cation and Cl− in the medium. Measurements of the efflux of H[14C]O 3 − or Cl− indicated that these anions were released from the cells into the NaCl or the NaHCO3 medium, respectively, probably by exchange in HCO 3 − /Cl−. Determination of intracellular ionic concentrations by electron microscopic X-ray microanalysis of cryopreserved specimens revealed that in the NaHCO3 medium, external Na+ (and probably HCO 3 − ) enters the gametocytes by exchange with internal Cl− (and probably H+), whereas in Cl−-containing media, external unspecified cation and Cl− influx by exchange, probably with H+ and HCO 3 − . It is therefore suggested that two separate ion exchangers, i.e., Na+-dependent HCO 3 − (in)/Cl−(out) and nonspecific monovalent-cation-dependent Cl−(in)/HCO 3 − (out) exchangers, are involved in the induction of gametogenesis inP. berghei. Furthermore, the presence of both classes of anion in the medium enhanced exflagellation activity and increased Na+ uptake more than did the NaCl or NaHCO3 medium alone. The apparent synergistic enhancement by two contraactive anion exchangers is consistent with a “recycling” model of pHi regulation, in which HCO 3 − and Cl− are exchanged between the cells and the media, resulting in the acceleration of monovalent cation/H+ exchange.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00937084
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  • 4
    Electronic Resource
    Electronic Resource
    Possible roles of cAMP and Ca2+ in the regulation of miracidial transformation inSchistosoma mansoni (1989)
    Springer
    Parasitology research 75 (1989), S. 368-374 
    Details
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The triggering action of physiological saline in the miracidial transformation ofSchistosoma mansoni was analyzed using various agents affecting cAMP-and Ca2+-dependent pathways. Potent activators of adenylate cyclase such as forskolin and serotonin, strongly inhibited the transformation provoked by saline in RPMI-1640. These inhibitory actions were diminished by the combined administration of phosphodiesterase activators such as ammonium salts or imidazole. Furthermore the exposure of miracidia to ammonium salts or imidazole in dechlorinated tap water “mimicked” the transformation, i.e., the cessation, of swimming and then shedding of epithelial plates. This mimic transformation was also inhibited by serotonin or forskolin. In contrast, treatment of miracidia with Ca2+ antagonists such as TMB-8 (an inhibitor of Ca2+ release), nicardipine (a Ca2+ channel blocker), or W-7 (a calmodulin inhibitor) in tap water produced severe vesiculation on their body surfaces and resulted in death. However, these toxic effects were abolished by a combined administration of these Ca2+ antagonists with saline or NH4Cl, and the transformation was reestablished except with W-7 treatment. W-7 strongly inhibited the triggering action of saline and NH4Cl and the worms swam slowly, whereas W-5, an inactive analogue of W-7, had no inhibitory effect on the transformation. These results suggest that the initiation of micracidial transformation to young sporocysts may be synergistically, regulated by cAMP and Ca2+ and that a decrease in cAMP levels and an increase in Ca2+ mobilization may be provoked in worms transformed by saline, ammonium salts, or imidazole.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00931132
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  • 5
    Electronic Resource
    Electronic Resource
    Detection of congenital malaria by polymerase-chain-reaction methodology in Dar es Salaam, Tanzania (2000)
    Springer
    Parasitology research 86 (2000), S. 615-618 
    Details
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The examination of congenital malaria was performed by Giemsa staining and polymerase-chain-reaction (PCR) methodology. We randomly selected 298 neonates who had been admitted to Muhimbili Medical Center (MMC) at Dar es Salaam, Tanzania. One baby among all the enrolled neonates was recognized as having a congenital malaria infection, which gave a prevalence of 0.33%. The present result was 5-fold the clinically recognized prevalence of congenital infection with malaria in the ward. The PCR method identified two cases, one of which was negative as determined by the Giemsa-staining method. Therefore, the PCR method was useful for the detection of scant amounts of malarial parasites in numerous blood samples. The screening of malaria by a sensitive PCR method contributes to reduce the mortality of asymptotic neonates in particular.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008540
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  • 6
    Electronic Resource
    Electronic Resource
    Penetration of the mosquito midgut wall by the ookinetes ofPlasmodium yoelii nigeriensis (1991)
    Springer
    Parasitology research 77 (1991), S. 230-236 
    Details
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The penetration route of ookinetes ofPlasmodium yoelii nigeriensis in the midgut of a mosquito,Anopheles omorii, was investigated by electron microscopy. Within 15–18 h after an infective blood meal, ookinetes could be seen in the midgut lumen in the process of entering the midgut wall, or lodged between the basement membrane and the basal lamina. The morphology of the ookinetes and their transformation into early oocysts were found to be similar to those previously reported. Ookinetes penetrated the midgut wall by the intercellular route; however, the intracellular occurrence of the parasite was also observed. Vacuoles appeared around the penetrating ookinetes during the penetration process, but no change in the electron density of the rhoptry-microneme complex was noted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00930863
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