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Parasitic Organisms (parasitic + organism)

Distribution by Scientific Domains

Life Sciences	60%

Selected Abstracts

Sex-specific genetic structure in Schistosoma mansoni: evolutionary and epidemiological implications

MOLECULAR ECOLOGY, Issue 7 2002
F. Prugnolle
Abstract We studied the population genetic structure of 360 and 1247 adult Schistosoma mansoni using seven microsatellite and seven random amplified polymorphic DNA (RAPD) markers, respectively. Parasites were collected from their natural definitive host Rattus rattus in Guadeloupe (West Indies). We found a sex-specific genetic structure, a pattern never before reported in a parasitic organism. Male genotypes were more randomly distributed among rats than female genotypes. This interpretation was consistent with a lower differentiation between hosts for males relative to females, the higher genetic similarity between females in the same host and the observed local (i.e. within-individual-host) differences in allele frequencies between the two sexes. We discuss our results using ecological and immunological perspectives on host,parasite relationships. These results change our view on the epidemiology of schistosomiasis, a serious disease affecting humans in African and American intertropical zones. [source]

Evolutionary analysis of fructose 2,6-bisphosphate metabolism

IUBMB LIFE, Issue 3 2006
Paul A. M. Michels
Abstract Fructose 2,6-bisphosphate is a potent metabolic regulator in eukaryotic organisms; it affects the activity of key enzymes of the glycolytic and gluconeogenic pathways. The enzymes responsible for its synthesis and hydrolysis, 6-phosphofructo-2-kinase (PFK-2) and fructose-2,6-bisphosphatase (FBPase-2) are present in representatives of all major eukaryotic taxa. Results from a bioinformatics analysis of genome databases suggest that very early in evolution, in a common ancestor of all extant eukaryotes, distinct genes encoding PFK-2 and FBPase-2, or related enzymes with broader substrate specificity, fused resulting in a bifunctional enzyme both domains of which had, or later acquired, specificity for fructose 2,6-bisphosphate. Subsequently, in different phylogenetic lineages duplications of the gene of the bifunctional enzyme occurred, allowing the development of distinct isoenzymes for expression in different tissues, at specific developmental stages or under different nutritional conditions. Independently in different lineages of many unicellular eukaryotes one of the domains of the different PFK-2/FBPase-2 isoforms has undergone substitutions of critical catalytic residues, or deletions rendering some enzymes monofunctional. In a considerable number of other unicellular eukaryotes, mainly parasitic organisms, the enzyme seems to have been lost altogether. Besides the catalytic core, the PFK-2/FBPase-2 has often N- and C-terminal extensions which show little sequence conservation. The N-terminal extension in particular can vary considerably in length, and seems to have acquired motifs which, in a lineage-specific manner, may be responsible for regulation of catalytic activities, by phosphorylation or ligand binding, or for mediating protein-protein interactions. IUBMB Life, 58: 133 - 141, 2006 [source]

Host specificity and geographic range in haematophagous ectoparasites

OIKOS, Issue 3 2005
Boris R. Krasnov
A negative interspecific correlation between the degree of habitat specialization and the size of a species' geographic range has been documented for several free living groups of organisms, providing support for the niche breadth hypothesis. In contrast, practically nothing is known about the geographic range sizes of parasitic organisms and their determinants. In the context of the niche breadth hypothesis, parasites represent ideal study systems, because of the well documented variation in host specificity among parasite species. Here, we investigated the relationship between host specificity (a measure of niche breadth) and geographic range size among flea species parasitic on small mammals, using data from seven distinct geographical regions. Two measures of host specificity were used: the number of host species used by a flea species, and a measure of the average taxonomic distance between the host species used by a flea; the latter index provides an evolutionary perspective on host specificity. After correcting for phylogenetic influences, and using either of our two measures of host specificity, the degree of host specificity of fleas was negatively correlated with the size of their geographic range in all seven regions studied here, with only one minor exception. Overall, these results provide strong support for the niche breadth hypothesis, although other explanations cannot be ruled out. [source]

Comparative analysis of glycosylinositol phosphorylceramides from fungi by electrospray tandem mass spectrometry with low-energy collision-induced dissociation of Li+ adduct ions

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2001
Steven B. Levery
Glycosylinositol phosphorylceramides (GIPCs) are a class of acidic glycosphingolipids (GSLs) expressed by fungi, plants, and certain parasitic organisms, but not found in cells or tissues of mammals or other higher animals. Recent characterizations of fungal GIPCs point to an emerging diversity which could rival that already known for mammalian GSLs, and which can be expected to present a multitude of challenges for the analytical chemist. Previously, the use of Li+ cationization, in conjunction with electrospray ionization mass spectrometry (ESI-MS) and low-energy collision-induced dissociation tandem mass spectrometry (ESI-MS/CID-MS), was found to be particularly effective for detailed structural analysis of monohexosylceramides (cerebrosides) from a variety of sources, including fungi, especially minor components present in mixtures at extremely low abundance. In applying Li+ cationization to characterization of GIPCs, a substantial increase in both sensitivity and fragmentation was observed on collision-induced dissociation of [M,+,Li]+ versus [M,+,Na]+ for the same components analyzed under similar conditions, similar to results obtained previously with cerebrosides. Molecular adduct fragmentation patterns were found to be systematic and characteristic for both the glycosylinositol and ceramide moieties with or without phosphate. Interestingly, significant differences were observed in fragmentation patterns when comparing GIPCs having Man,1,,,2 versus Man,1,,,6Ins core linkages. In addition, it was useful to perform tandem product ion scans on primary fragments generated in the orifice region, equivalent to ESI-(CID-MS)2 mode. Finally, precursor ion scanning from appropriate glycosylinositol phosphate product ions yielded clean molecular ion profiles in the presence of obscuring impurity peaks. The methods were applied to detailed characterization of GIPC fractions of increasing structural complexity from a variety of fungi, including a non-pathogenic Basidiomycete (mushroom), Agaricus blazei, and pathogenic Euascomycete species such as Aspergillus fumigatus, Histoplasma capsulatum, and Sporothrix schenckii. The analysis confirmed a remarkable diversity of GIPC structures synthesized by the dimorphic S. schenckii, as well as differential expression of both glycosylinositol and ceramide structures in the mycelium and yeast forms of this mycopathogen. Mass spectrometry also established that the ceramides of some A. fumigatus GIPC fractions contain very little 2-hydroxylation of the long-chain fatty- N -acyl moiety, a feature that is not generally observed with fungal GIPCs. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Report of an unusual case of a conjunctival cyst with Liesegang rings

CLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 3 2009
Jaime Levy MD
Abstract Liesegang rings are laminated precipitation structures well recognized in the field of chemistry. We present a rare case of a 64-year-old man who sought examination for a conjunctival cystic lesion of several months' duration, located in the right nasal bulbar conjunctiva near the plica semilunaris. The lesion was excised completely and uneventfully under local anaesthesia. Histopathological examination revealed a large folded cyst in the substantia propria. The cyst contained multiple eosinophilic concentrically spherical and oval structures of variable size with an amorphous central core compatible with Liesegang rings. No fungal or parasitic organisms were identified. This is the first photographically documented case of Liesegang rings appearing in the conjunctiva. Liesegang ring formation should be taken into account during histopathological examination of a conjunctival cyst and not be misdiagnosed as a parasitic infection. [source]