Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “parasite”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,711 records · Page 95Linked to original sources

Localisation of hypoxanthine phosphoribosyl transferase in the malaria parasite Plasmodium falciparum.

The enzyme hypoxanthine phosphoribosyl transferase of the human malaria parasite Plasmodium falciparum has been located in parasites and parasite-infected erythrocytes by antibody probing. The probe was a polyclonal rabbit antiserum made against the parasite enzyme made in Escherichia coli. The enzyme is associated with membrane-bound compartments in merozoites and asexual blood parasites. In particular, indirect immunofluorescence studies reveal the enzyme localized in vesicle-like structures within the cytoplasm of the infected erythrocyte. This is the first time a P. falciparum protein of defined metabolic function has been tracked to a site outside the parasite cytosol. Studies on the targeting of the enzyme using a cell-free system suggests that the protein reaches its destination via a route different from the normal secretory pathway.

Amino Acid Sequence↗

Relation of the stage of parasite development in the peripheral blood to prognosis in severe falciparum malaria.

Admission blood films from 72 patients who died of severe falciparum malaria (50 Thai adults, 22 Gambian children) were matched retrospectively for parasitaemia with equal numbers of survivors. The peripheral blood parasites from fatal cases were more mature than those from survivors. Tiny rings (TR) comprised > 50% of parasites in 47/72 (65%) survivors but only 12/72 (17%) of fatal cases (P < 0.001). Parasites containing visible pigment (MTS: mature trophozoites and schizonts) comprised < 20% of the total parasite count in 10/72 (14%) survivors compared with 31/72 (43%) fatal cases (P < 0.001). Of the 39 patients with > 10(4) MTS/microL, 30 (81%) died. These findings were confirmed in a prospective study of 279 adult Thai patients admitted sequentially with acute falciparum malaria. Only 4 of the 19 fatal cases (21%) had > 50% TR, compared with 130 of 260 (50%) survivors, whereas > 20% MTS were found in 10/19 (53%) fatal cases, compared with 28/108 (27%) severe malaria survivors, and 26/155 (17%) patients with moderately severe malaria (P = 0.001). As a predictor of fatal outcome, the finding of either > 10(4) MTS/microL or > 5 x 10(5) parasites/microL in severe malaria had a sensitivity of 90% (95% confidence interval [CI] = 75-97%) and a specificity of 72% (95% CI = 59-86%). These observations are consistent with the hypothesis that a predominance of mature parasites in the peripheral blood reflects a greater sequestered biomass, and thus more severe disease. Simple microscopical assessment of parasite maturity on an admission blood slide provides important pathophysiological and prognostic information in severe falciparum malaria.

Adult↗

Identification of parasite proteins in a membrane preparation enriched for the surface membrane of erythrocytes infected with Plasmodium knowlesi.

A subcellular fraction enriched in erythrocyte membranes has been isolated from rhesus monkey erythrocytes infected with Plasmodium knowlesi. Infected cells were lysed by centrifugation through a zone of hypotonic buffer and membranes isolated by equilibrium density gradient centrifugation in the same tube. The purified membrane fraction was shown to include the erythrocyte surface membrane by several methods: electron microscopy, identification of Coomassie Blue stained erythrocyte membrane proteins, identification of band 3 with a monoclonal antibody, and identification of radioiodinated cell surface proteins. The resulting ghosts were shown to be specifically reactive with monkey sera against the variant surface antigens of P. knowlesi by indirect immunofluorescence and membrane agglutination. No reactivity was seen with a monoclonal antibody (13C11) against the intracellular schizont surface. A number of metabolically labelled parasite proteins were enriched in this membrane function, including peptides of 277, 208, 173, 153, 134, 109, 80, 60 and 48 kDa and the variant surface antigens of variable molecular mass (180-207 kDa). These proteins were distinct from the major parasite proteins of total infected erythrocytes and isolated merozoites. The major glucosamine labelled glycoprotein of the internal schizont (230 kDa) was not found in this fraction. Moreover, no fragment of this parasite glycoprotein was found in this membrane fraction, indicating that no part of this molecule is transported to the erythrocyte surface. In contrast, the variant antigen of P. knowlesi, known to be on the erythrocyte surface, could be readily identified as peptides unique to specific cloned parasite lines. We propose that the other nine parasite proteins found within this membrane fraction represent a starting point for the identification of other parasite proteins transported to the surface membrane of the infected erythrocyte.

Animals↗

Parasites as biological tags.

Parasites suffer from bad public relations. In The Goodness of Parasitism: A New Hypothesis, Lincicome proclaimed 'Parasitism, one of life's great phenomena, possesses a quality of goodness that has largely been overlooked because man has been so possessed with the disease aspects of this association'. It has been twenty years since Lincicome led the call for parasites' acceptance as admirable organisms, apparently without much success. Here, Mike Moser offers a brief reminder of the virtues of parasites and the benefits of being parasitized.

Journal Article↗

Resistance to Ascaris suum in parasite naïve and naturally exposed growers, finishers and sows.

Commercially reared growers, finishers, and sows of Danish Landrace x Yorkshire crossbred were inoculated orally with Ascaris suum at 50 eggs kg-1 body weight. White spots on the serosal surface of livers and total larval recoveries from lungs were recorded 7 days later. The response in pigs originating from a specific pathogen free and parasite free herd (parasite naïve) was observed in the three different age groups and compared with age-matched pigs from a herd maintained in a facility contaminated with A. suum (naturally exposed). The pre-inoculation immune status of the various groups was characterized serologically using antigen preparations derived from various stages of A. suum. Inoculation of all age groups of parasite naïve pigs with A. suum eggs produced relatively high liver white spots and lung larvae, although expression of these counts as a percentage of the inoculum showed a moderate age-related resistance from growers to finishers to sows. In contrast, pigs naturally exposed to A. suum expressed strong immunity to a challenge infection as few or no larvae were detected in the lungs. In addition, growers, finishers, and sows from the naturally exposed herd had significantly higher levels of serum IgG/IgA to several different A. suum antigens compared with pigs from the parasite nave herd. Liver white spots, expressed as a percentage of the inoculum, were highest in growers from the naturally exposed herd but were markedly reduced in finishers and sows from that herd. In fact, few or no white spots were observed in naturally exposed sows, while sows from the parasite-naïve herd had in excess of 300 liver white spots following challenge. These results indicate that commercially raised pigs that are exposed to A. suum develop a strong protective immunity that ultimately produces a complete pre-hepatic barrier to larval migration, while pigs raised parasite free remain susceptible to infection.

Age Factors↗

The use of impregnated curtains does not affect antibody responses against Plasmodium falciparum and complexity of infecting parasite populations in children from Burkina Faso.

In Burkina Faso, where malaria is hyper-endemic and transmission intensity is very high, the majority of malaria-related morbidity and mortality occurs in children less than 5 years of age. A control measure such as the use of insecticide-treated curtains (ITC) significantly reduces transmission of malaria infection. Concerns remain whether reduced transmission intensity may lead to a delay in the development of immunity in younger children and even to a partial loss of already acquired immunity. In this study, the levels of P. falciparum-specific IgG subclasses, the number of infecting parasite clones determined by PCR-based genotyping of the msp2 gene and the parasite density were analysed in 154 asymptomatic children (3-6 years) living in 16 villages (8 with and 8 without ITC) in the vicinity of Ouagadougou, the capital of Burkina Faso. In addition, the parasite inhibitory effects of Ig fractions, prepared from selected children, in co-operation with normal human monocytes were studied. Blood samples from asymptomatic ITC-users showed a significant decrease in P. falciparum prevalence as well as in parasite density. However, no significant difference was observed in P. falciparum-specific antibodies or in parasite multiplicity of infection between the two groups. Furthermore, Ig fractions from children of both groups showed similar levels of inhibitory activity against autologous parasite growth both on their own and in co-operation with monocytes.

Animals↗

Regulation of guanylyl cyclase by intracellular Ca2+ in relation to the infectivity of the protozoan parasite, Leishmania donovani.

A neuronal type Ca2+ stimulated nitric oxide synthase was earlier reported by us to be present in the protozoan parasite Leishmania donovani. As part of nitric oxide-cyclic GMP transduction signaling operative in higher eukaryotes and involved in the long-term potentiation, a soluble guanylyl cyclase has also been detected in this lower eukaryote. However, detailed biochemical characterization revealed the enzyme to be Ca2+ modulated and unstimulated by nitric oxide donors as opposed to higher eukaryotes. The possible role of intracellular Ca2+ level in the regulation of guanylyl cyclase activity as well as L. donovani infectivity was explored by measuring the intracellular survival of the parasites in mammalian macrophages after treatments, which decrease or elevate the intracellular Ca2+. Parasites loaded with intracellular Ca2+ chelators displayed significantly decreased infectivity and cyclic GMP level. In contrast, pretreatment with Ca2+ ionophores, which elevated Ca2+ levels in L. donovani, significantly enhanced the cyclic GMP level as well as the infectivity of the parasites. Moreover, treatment with selective inhibitors of soluble guanylyl cyclase also reduced infectivity, even in cases of calcium ionophore-treated parasites. The gene encoding the soluble guanylyl cyclase was cloned, sequenced and over expressed in bacterial system. The recombinant protein showed enzyme characteristics similar to that obtained in L. donovani promastigote cytosol. Together these results suggest a possible link between guanylyl cyclase, intracellular Ca2+ content and parasite infectivity.

Amino Acid Sequence↗

Toxoplasma gondii grown in human cells uses GalNAc-containing glycosylphosphatidylinositol precursors to anchor surface antigens while the immunogenic Glc-GalNAc-containing precursors remain free at the parasite cell surface.

Toxoplasma gondii is a ubiquitous parasite that infects nearly all warm-blooded animals. Developmental switching in T. gondii, from the virulent tachyzoite to the relatively quiescent bradyzoite stage, is responsible for the disease propagation after alteration of the immune status of the carrier. The redifferentiation event is characterized by an over expression of a tachyzoite specific set of glycosylphosphatidylinositol anchored surface antigens and free GPIs. T. gondii grown in animal cells uses two glycosylphosphatidylinositol precursors to anchor the parasite surface proteins. The first form has an N-acetylgalactosamine residue bound to a conserved three-mannosyl core glycan, while the second structure contains an additional terminal glucose linked to the N-acetylgalactosamine side branch. Sera from persons infected with T. gondii reacted only with the glucose-N-acetylgalactosamine-containing structure. Here we report that T. gondii cultured in human cells uses predominantly the N-acetylgalactosamine-containing structure to anchor the parasite surface antigens. On the other hand, glycosylphosphatidylinositol structures having an additional terminal glucose are found exclusively on the parasite cell surface as free glycolipids participating in the production of cytokines that are implicated in the pathogenesis of T. gondii. We also provide evidence that such free glycosylphosphatidylinositols are restricted mainly to the lipid microdomains in the parasite cell surface membrane and mostly associated with proteins involved in the parasite motility as well as invasion of the host cell.

Animals↗

Membrane transformation during malaria parasite release from human red blood cells.

Three opposing pathways are proposed for the release of malaria parasites from infected erythrocytes: coordinated rupture of the two membranes surrounding mature parasites; fusion of erythrocyte and parasitophorus vacuolar membranes (PVM); and liberation of parasites enclosed within the vacuole from the erythrocyte followed by PVM disintegration. Rupture by cell swelling should yield erythrocyte ghosts; membrane fusion is inhibited by inner-leaflet amphiphiles of positive intrinsic curvature, which contrariwise promote membrane rupture; and without protease inhibitors, parasites would leave erythrocytes packed within the vacuole. Therefore, we visualized erythrocytes releasing P. falciparum using fluorescent microscopy of differentially labeled membranes. Release did not yield erythrocyte ghosts, positive-curvature amphiphiles did not inhibit release but promoted it, and release of packed merozoites was shown to be an artifact. Instead, two sequential morphological stages preceded a convulsive rupture of membranes and rapid radial discharge of separated merozoites, leaving segregated internal membrane fragments and plasma membrane vesicles or blebs at the sites of parasite egress. These results, together with the modulation of release by osmotic stress, suggest a pathway of parasite release that features a biochemically altered erythrocyte membrane that folds after pressure-driven rupture of membranes.

Animals↗

In vitro activity of the beta-carboline alkaloids harmane, harmine, and harmaline toward parasites of the species Leishmania infantum.

Harmane, harmine, and harmaline were investigated for their in vitro antileishmanial activity toward parasites of the species Leishmania infantum. Harmane and Harmine displayed a moderate antiproliferative activity toward human monocytes and exerted a weak antileishmanial activity toward both the promastigote and the amastigote forms of the parasite. Their mechanism of action on the promastigote form of the parasite involved interactions with DNA metabolism leading to an accumulation of parasites in the S-G(2)M phases of the cell-cycle. Harmaline, at the contrary, was deprived from toxicity toward human cells and Leishmania promastigotes, however it exerted a strong antileishmanial activity toward the intracellular amastigote form of the parasite. This property was shown to partly result from the capacity of the molecule to prevent parasite internalization within macrophages by inhibiting Leishmania PKC activity.

Animals↗

How do obligate parasites evolve? A multi-gene phylogenetic analysis of downy mildews.

Plant parasitism has independently evolved as a nutrition strategy in both true fungi and Oomycetes (stramenopiles). A large number of species within phytopathogenic Oomycetes, the so-called downy mildews, are defined as obligate biotrophs since they have not, to date, been cultured on any artificial medium. Other genera like Phytophthora and Pythium can in general be cultured on standard or non-standard agar media. Within all three groups there are many important plant pathogens responsible for severe economic losses as well as damage to natural ecosystems. Although they are important model systems to elucidate the evolution of obligate parasites, the phylogenetic relationships between these genera have not been clearly resolved. Based on the most comprehensive sampling of downy mildew genera to date and a representative sample of Phytophthora subgroups, we inferred the phylogenetic relationships from a multi-gene dataset containing both coding and non-coding nuclear and mitochondrial loci. Phylogenetic analyses were conducted under several optimality criteria and the results were largely consistent between all the methods applied. Strong support is achieved for monophyly of a clade comprising both the genus Phytophthora and the obligate biotrophic species. The facultatively parasitic genus Phytophthora is shown to be at least partly paraphyletic. Monophyly of a cluster nested within Phytophthora containing all obligate parasites is strongly supported. Within the obligate biotrophic downy mildews, four morphologically or ecologically well-defined subgroups receive statistical support: (1) A cluster containing all species with brownish-violet conidiosporangia, i.e., the genera Peronospora and Pseudoperonospora; (2) a clade comprising the genera with vesicular to pyriform haustoria (Basidiophora, Benua, Bremia, Paraperonospora, Plasmopara, Plasmoverna, Protobremia); (3) a group containing species included in Hyaloperonospora and Perofascia which almost exclusively infect Brassicaceae; (4) a clade including the grass parasites Viennotia oplismeni and Graminivora graminicola. Phylogenetic relationships between these four clades are not clearly resolved, and neither is the position of Sclerospora graminicola within the downy mildews. Character analysis indicates an evolutionary scenario of gradually increasing adaptation to plant parasitism in Peronosporales and that at least the most important of these adaptive steps occurred only once, including major host shifts within downy mildews.

Animals↗

Foodborne protozoan parasites.

This report addresses Cryptosporidium, Giardia, Cyclospora, and more briefly, Toxoplasma as the main parasitic protozoa of concern to food production worldwide. Other parasitic protozoa may be spread in food or water but are not considered as great a risk to food manufacture. The protozoan parasites Cryptosporidium, Giardia, and Cyclospora have proven potential to cause waterborne and foodborne disease. Toxoplasma gondii has been considered a risk in specific cases, but humans are not its primary host. Cryptosporidium and Giardia are widespread in the environment, particularly the aquatic environment, and major outbreaks of cryptosporidiosis and giardiasis have occurred as a result of contaminated drinking water. Large outbreaks of waterborne cyclosporiasis have not been identified. Cryptosporidium, Giardia, and Cyclospora have potential significance in the preparation and consumption of fresh produce and in catering practice, in which ready-to-eat foods may be served that have not received heat treatment. None of the three organisms Cryptosporidium, Giardia, and Cyclospora has been shown to be a problem for heat processed food or tap water that has undergone appropriate treatment at a water treatment works. All three are sensitive to standard pasteurisation techniques. Although humans are not a primary host for T. gondii, the potential exists for both waterborne and foodborne toxoplasmosis. Parasitic protozoa do not multiply in foods, but they may survive in or on moist foods for months in cool, damp environments. Their ecology makes control of these parasites difficult. For general control of parasitic protozoa in the food chain, the following steps are necessary: - Follow good hygienic practice in food service and catering industries.- Minimise dissemination of cysts and oocysts in the farming environment and via human waste management.- Include these microorganisms in Hazard Analysis Critical Control Point (HACCP) plans of water suppliers, industries or sectors that use fresh produce, and operations in which contaminated process or ingredient water could end up in the product (e.g., where water supplies may become contaminated).

Animals↗

Heritable transgenesis of Parastrongyloides trichosuri: a nematode parasite of mammals.

Germline transformation of a parasitic nematode of mammals has proven to be an elusive goal. We report here the heritable germline transformation of Parastrongyloides trichosuri, a nematode parasite whose natural hosts are Australian possums of the genus Trichosurus. This parasite can undergo multiple free-living life cycles and these replicative cycles can be maintained indefinitely in the laboratory. Transformation was achieved by microinjection of DNA into the ovary syncytium of either free-living or parasitic adult females. By selecting for the transgenic progeny of successive free-living life cycles, it was possible to establish and maintain transgenic lines. All three transgenic lines tested were shown capable of establishing patent infections in possums and to transmit the functional transgene to their progeny. The transgene, driven by the Pt hsp-1 promoter, was constitutively expressed in intestinal cells at all stages of both parasitic and free-living life cycles, although gene silencing appears to occur in some transgenic progeny. This is the first report of heritable transgenesis in a parasitic nematode of a mammal and we discuss a variety of previously inaccessible experimental avenues that will now be possible with this powerful model system.

Animals↗

Quantitative chromatographic determination of several benzimidazole anthelmintic molecules in parasite material.

A specific, precise and accurate high-performance liquid chromatographic (HPLC) analytical method has been developed for the quantitative determination of different benzimidazole (BZD) anthelmintics in parasite material (Moniezia benedeni). Mebendazole (MBZ), oxibendazole (OBZ), flubendazole (FLBZ), albendazole (ABZ) ricobendazole (RBZ), albendazole sulphone (ABZSO(2)), fenbendazole (FBZ), oxfendazole (OFZ) and fenbendazole sulphone (FBZSO(2)) were measured simultaneously in M. benedeni, a sheep and cattle cestode parasite used as a model of the biological matrix. The recovery, linearity, precision, accuracy, limits of detection and quantification of the method were determined. Drug extraction from the parasite's tissue homogenate was performed using methanol (liquid phase extraction), and after solvent evaporation, the residual material was cleaned up by solid phase extraction prior to analysis by reversed-phase HPLC. The resolution of all the BZD molecules assayed was obtained on a C(18) reversed-phase (5 microm, 250 mm x 4.6 mm) column using acetonitrile and ammonium acetate as the mobile phase and ultraviolet (UV) detection at 292 nm. Regression analyses for all the BZD compounds assayed were linear at concentrations ranging from 1.61 to 64.21 nmol/100mg protein (triplicate determinations) showing correlation coefficients greater than 0.9922. The developed method is efficient for the simultaneous determination of several benzimidazole anthelmintic molecules in parasite material and useful for the ex vivo and in vivo characterisation of the kinetics of drug uptake/diffusion in target parasites, which seems to be relevant to optimise parasite control both in human and veterinary medicine.

Animals↗

A new parasite that infects eggs of the mud crab, Scylla serrata, in Australia.

The mud crab, Scylla serrata, is currently being evaluated for its feasibility for mass aquaculture in Australia. As part of the evaluation process, pathogens that can affect this species need to be identified. This research note describes a possible new parasite that infects the eggs of S. serrata. The parasite was discovered in two separate cases (three months apart) in a broodstock research program and appears to cause 100% egg mortality. The parasite consists of a cluster of cells with rhizoids that appear to function as an anchorage and a feeding organ. The individual cells range from 3 to 6 microm with a single nucleus. The parasite could not be classified to a phylum by morphology alone. However, BLAST analysis of the DNA sequence from a PCR amplicon generated using universal 18S ribosomal RNA gene primers indicated similarity to pathogenic thraustochytrids, Dermocystidium sp. and Rhinosporidium seeberi. All except R. seeberi are protistan parasites of fish and crustaceans. A neighbour-joining phylogenetic tree confirmed the homology with the thraustochytrids; however, further molecular techniques need to be exploited for absolute classification of this new parasite.

Animals↗

Sudanese mucosal leishmaniasis: isolation of a parasite within the Leishmania donovani complex that differs genotypically from L. donovani causing classical visceral leishmaniasis.

Mucosal leishmaniasis, which is a sporadic disease in the Sudan, was shown by isoenzyme characterization and PCR to be caused by Leishmania donovani. However, it was not clear if the parasite was exactly the same strain as that causing visceral leishmaniasis (VL), or of a different strain. We utilized a new generation of molecular DNA markers, minisatellites and kinetoplast DNA, for rapid characterization of the parasite. The results show that the genotypes of some of the parasites causing VL are different from those causing mucosal leishmaniasis. The L. donovani isolates causing visceral disease, as well as post-kala-azar mucosal leishmaniasis (PKML), have been shown to possess characteristic haplotypes. However, sequencing of a portion of the cytochrome oxidase II (COII) gene indicates that the parasite that invades the oral mucosa is divergent from other parasites causing VL. It appears to possess features of a more ancestral parasite with pronounced sequence homology to L. major. This agrees with earlier studies where isolates of mucosal leishmaniasis have been shown to possess an isoenzyme profile distinct from L. donovani and a different geographical distribution, albeit often overlapping with that of L. donovani.

Aged↗

Parasite-derived trans-sialidase binds to heart tissue in Trypanosoma cruzi-infected animals.

Trypanosoma cruzi is an obligate intracellular protozoan parasite that actively penetrates into non-phagocytic mammalian cells. To accomplish this, the parasite relies on the binding of cell surface ligands. It is reported herein that the T. cruzi trans-sialidase (TS), which is exposed on the parasite surface, binds to mouse heart cells, and should therefore be further studied as a possible cell penetration-related ligand. In addition, as has been proposed elsewhere, the binding of T. cruzi to tissues may turn them into targets for parasite-specific immune reactions. Washed heart sections from T. cruzi-infected mice were subjected to immunoenzymatic staining with antisera against whole T. cruzi and with polyclonal or monoclonal antibodies against TS. The anti-TS antibodies stained both parasites and uninfected heart cells in the vicinity of T. cruzi nest remains/trypomastigotes. On the other hand, an anti-T. cruzi serum, which did not recognize TS, only stained the parasites. In addition, normal heart sections from uninfected nude mice were shown to react with both enzymatically active and inactive recombinant TS molecules, probably through their amino-terminal region, since a recombinant TS lacking this region failed to bind.

Animals↗

Parasite genetics and the immune host: recombination between antigenic types of Eimeria maxima as an entrée to the identification of protective antigens.

The genomes of protozoan parasites encode thousands of gene products and identification of the subset that stimulates a protective immune response is a daunting task. Most screens for vaccine candidates identify molecules by capacity to induce immune responses rather than protection. This paper describes the core findings of a strategy developed with the coccidial parasite Eimeria maxima to rationally identify loci within its genome that encode immunoprotective antigens. Our strategy uses a novel combination of parasite genetics, DNA fingerprinting, drug-resistance and strain-specific immunity and centres on two strains of E. maxima that each induce a lethal strain-specific protective immune response in the host and show a differential response to anti-Eimeria chemotherapy. Through classical mating studies with these strains we have demonstrated that loci encoding molecules stimulating strain-specific protective immunity or resistance to the anti-coccidial drug robenidine segregate independently. Furthermore, passage of populations of recombinant parasites in the face of killing in the immune host was accompanied by the elimination of some polymorphic DNA markers defining the parent strain used to immunise the host. Consideration of the numbers of parasites recombinant for the two traits implicates very few antigen-encoding loci. Our data provide a potential strategy to identify putative antigen-encoding loci in other parasites.

Animals↗