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PubMed2000

Plasmodium falciparum-infected erythrocytes: qualitative and quantitative analyses of parasite-induced knobs by atomic force microscopy.

We used the combination of an atomic force microscope and a light microscope equipped with epifluorescence to serially image Plasmodium falciparum-infected erythrocytes. This procedure allowed us to determine unambiguously the presence and developmental stage of the malaria parasite as well as the number and size of knobs in singly, doubly, and triply infected erythrocytes. Knobs are not present during the ring stage of a malaria infection but a lesion resulting from invasion by a merozoite is clearly visible on the erythrocyte surface. This lesion is visible into the late trophozoite stage of infection. Knobs begin to form during the early trophozoite stage of infection and have a single-unit structure. Our data suggest the possibility that a two-unit structure of knobs, which was reported by Aikawa et al. (1996, Exp. Parasitol. 84, 339-343) using atomic force microscopy, appears to be a double-tipped image. The number of knobs per unit of host cell surface area is directly proportional to parasite number in both early and late trophozoite stages. These results indicate that knob formation by one parasite does not influence knob formation by other parasites in a multiply infected erythrocyte. In addition, knob volume is not influenced by either parasite stage or number at the late trophozoite stage, indicating that the number of component molecules per knob is constant throughout the parasite maturation process.

Animals↗
PubMed1998

The Coexistence of Competing Parasites. Part II-Hyperparasitism and Food Chain Dynamics.

Hyperparasitism is a widespread interaction in natural communities, but has to date received little attention in the theoretical literature. In this paper, we compared canonical models for food chains (resource-prey-predator systems) and host-parasite-hyperparasite interactions. We focus on microparasites, so the dynamical variables are the abundances of host individuals in different classes (e.g. with or without a particular parasite), and assume that the parasite is the only factor regulating a host population. Analysis of a "donor-controlled" model in which the primary parasite regulates host population growth, but with no additional demographic impact of the hyperparasite, suggests that intrinsic growth rate r of the host population is a fundamental parameter governing persistence of the hyperparasite. We then examine a model in which the hyperparasite can affect host births, deaths, and rate of recovery from the primary parasite. A wide range of outcomes are possible. For instance, hyperparasites can stabilize inherently unstable host-parasite systems, or destabilize stable systems. Persistence at a stable equilibrium often requires that the host intrinsic growth rate r lie within defined bounds; at low r, the hyperparasite may not be able to persist (in stable systems), whereas at high r the system is unstable and the host population grows in an unbounded fashion. We conclude by sketching directions for future work, and suggesting some possible practical implications of our results.Copyright 1998 Academic Press

Journal Article↗
PubMed1987

Treatment of fish parasites. 2. Effects of praziquantel, niclosamide, levamisole-HCl, and metrifonate on monogenea (Gyrodactylus aculeati, Diplozoon paradoxum).

In research for successful treatment of fish parasitized by monogeneans, four substances (Praziquantel, Niclosamide, Levamisole-HCl, and Metrifonate) were tested in vivo against Gyrodactylus aculeati parasitizing the skin of sticklebacks (Gasterosteus aculeatus). Fish were incubated in water containing different solutions of the drugs. Praziquantel, Niclosamide and Levamisole-HCl were effective against Gyrodactylus aculeati. Praziquantel caused irreversible lesions in the parasite tegument (beginning with 1 microgram/ml and 90 min exposure). Niclosamide was effective in a narrow concentration range of 0.075-0.1 microgram/ml (90 min). Levamisole-HCl was effective in a concentration range of 20-50 micrograms/ml for 120 min. Like Praziquantel, Niclosamide and Levamisole-HCl led to damage of the parasite tegument. The opisthaptor region and the openings of the cephalic glands were most severely affected. Furthermore, the effects of Niclosamide, Levamisole-HCl and Metrifonate on Diplozoon paradoxum parasitizing the gills of chubs (Squalius cephalus) and breams (Abramis brama) were investigated. Levamisole-HCl (10 micrograms/ml) and Niclosamide (0.2 microgram/ml) were effective against Diplozoon paradoxum after an exposure of 90 min and 45 min in vitro. The parasites were severely affected along the midbody. Metrifonate caused a lysis of the tegument and a strong secretion of slime. It is suggested that chemotherapy against Gyrodactylus sp. may be accomplished with 10 mg Praziquantel/l for 3 h during storage in smaller tanks. Niclosamide (0.1 mg/l for 90 min), or Levamisole-HCl (50 mg/l for 120 min) may be used alternatively. Concentrations of Niclosamide and Levamisole-HCl have to be calculated with accuracy, since fish only tolerate a very narrow range of these drugs (Niclosamide: 0.1 mg/l for 120 min; Levamisole-HCl: 50 mg/l for 120 min).

Animals↗
PubMed1986

IgE response in Strongyloides ratti-infected rats with special reference to the life cycle of the parasite.

Parasite-specific IgE antibody response was examined in Strongyloides ratti-infected rats. The results showed that the parasite-specific IgE antibody response was generated after a primary infection. However, repeated infections rather depressed the level of parasite-specific IgE antibody in the serum. Immunization limited to specific stages of the parasite revealed that stimulation of parasite-specific IgE antibody was related to the intestinal adult stage. On the other hand, depression of IgE titers was related to the tissue-migrating larval stage. The capacity of the each stage of the parasite to induce specific IgE response may be related to the variable results of the IgE responses in human strongyloidiasis.

Animals↗
PubMed1992

Rapid transport of the acidic phosphoproteins of Plasmodium berghei and P. chabaudi from the intraerythrocytic parasite to the host membrane using a miniaturized fractionation procedure.

A miniaturized procedure for the separation of the host erythrocyte membrane from malarial parasites based on saponin lysis and density-gradient centrifugation with Percoll is described. The procedure requires only 20-35 microliters packed infected erythrocytes, is simple to perform, needs no sophisticated equipment, and can be completed in less than 2 h. Analysis of the isolated erythrocyte membranes and parasites using marker enzymes and electron microscopy revealed that both the purity and the yield of these fractions were relatively high. Erythrocyte membrane proteins, including spectrin, ankyrin, and band 4.1, were not found on the parasitophorous vacuolar membrane, which remained associated with some but not all of the isolated parasites. Application of this method to pulse-chase experiments indicated that the acidic phosphoproteins of Plasmodium berghei and P. chabaudi were rapidly transported from the parasite to the erythrocyte membrane immediately after their synthesis. The rapid export of these acidic phosphoproteins from the parasite distinguishes them from other proteins exported by the malarial parasite.

Animals↗
PubMed1982

Bovine fascioliasis in Nigeria--intercurrent parasitic and bacterial infections.

The bacterial and parasitic infections associated with field cases of bovine fascioliasis due to Fasciola gigantica were investigated; 47.6% of infected cattle had blood parasites, 61.9% had faecal-borne parasites and 85.8% had positive bacterial isolates in the bile in contrast to 13.3% with blood parasites, 71.1% with faecal-borne parasites and 28.9% positive for bile bacteria among uninfected cattle. Trypanosoma spp., Babesia, Paramphistomum and Schistosoma were the most commonly found parasites associated with fascioliasis. On the other hand Staphylococcus pyogenes, Escherichia coli and mixed infections of these with other Enterobacteriaceae were the common bacteria isolated from the bile of infected cattle. The parasitaemia of Babesia was significantly higher in infected than uninfected cattle but there was no significant difference in strongyle egg count between the 2 groups of cattle.

Animals↗
PubMed2002

Indirect effects of heavy metals on parasites may cause shifts in snail species compositions.

We studied the direct and indirect effects of pollution on the distributions and abundances of two closely related species of pulmonate freshwater snails. Physella columbiana is more numerous at heavy metal-polluted lakes, and Lymnaea palustris is more numerous at reference lakes. Both species are present at all sites, as are predatory bluegill sunfish (Lepomis macrochirus). The direct effects examined included the snails' growth and reproduction in both the presence and absence of heavy metals and their short-term survival when exposed to large concentrations of heavy metals. The indirect effects were the species' ability to elude capture by sunfish and the diversity and abundance of parasites within the snails. We found that heavy metals had little direct effect on growth and reproduction and that both species acquired similar levels of metals in their tissues. Interestingly, P. columbiana (the more abundant species in polluted lakes) actually exhibited higher recruitment in the absence of metals than did L. palustris (reference lakes). L. palustris has life history characteristics that favor increased growth and reduced reproduction. These characteristics resulted in decreased predation of adults by gape-limited predators and a greater ability to cope with heavy parasite burdens. P. columbiana exhibited slower growth, which resulted in increased predation although higher reproduction rates may compensate.The major effect of heavy metals on species distributions was indirect on the snails' parasites. Parasites appeared to be very susceptible to metals, and this resulted in lower parasite diversity and intensities at polluted sites for both species of snails. P. columbiana may only be able to outcompete L. palustris at polluted sites due to the indirect effects of heavy metals; the negative effect of heavy metals on parasites, and a proposed negative effect of metals on the foraging ability of sunfish that favors the faster-reproducing P. columbiana.

Animals↗
PubMed2002

The FAR proteins of parasitic nematodes: their possible involvement in the pathogenesis of infection and the use of Caenorhabditis elegans as a model system to evaluate their function.

Parasitic nematodes secrete a structurally novel class of fatty acid and retinol-binding (FAR) protein into the surrounding tissues of the host. These proteins are of interest because they may play an important role in scavenging fatty acids and retinoids from the host that are essential for the survival of the parasite and also because the localised depletion of such lipids may have immunomodulatory effects that compromise the host immune response. Research into the biological function(s) of the FAR proteins has been severely hampered by the difficulties associated with the life-cycle propagation of parasitic nematodes and the current intractability of the parasites to reverse-genetic studies. The genome of the free-living nematode Caenorhabditis elegans, however, encodes eight FAR-like proteins, and in this review we compare the FAR proteins of C. elegans and parasitic nematodes, and we discuss the suitability of C. elegans as a model system to investigate the biological function(s) of the FAR proteins of parasitic nematodes.

Amino Acid Sequence↗
PubMed2002

Traffic pathways of Plasmodium vivax antigens during intraerythrocytic parasite development.

We investigated the secretory traffic of a Plasmodium vivax antigen (Pv-148) synthesised by the parasite during the blood cycle, exported into the host cell cytosol and then transported to the surface membrane of the infected erythrocyte. Studies of the ultrastructure of erythrocytes infected with P. vivax showed that intracellular schizogony is accompanied by the generation of parasite-induced membrane profiles in the erythrocyte cytoplasm. These structures are detectable soon after the parasite invades the erythrocyte and develop an elaborate organisation, leading to a tubovesicular membrane (TVM) network, in erythrocytes infected with mature trophozoites. Interestingly, the clefts formed stacked, flattened cisternae resembling a classical Golgi apparatus. The TVM network stained with the fluorescent Golgi marker Bodipy-ceramide. Specific immunolabelling showed that Pv-148 was transferred from the parasite to the erythrocyte surface membrane via the clefts and the TVM network. These findings suggest that the TVM network is part of the secretory pathways involved in parasite protein transport across the Plasmodium-infected erythrocyte and that Pv- 148 may represent a marker that links the parasite with the host cell cytoplasm and, in turn, with the extracellular milieu.

Animals↗
PubMed2002

Accumulation of human waterborne parasites by zebra mussels (Dreissena polymorpha) and Asian freshwater clams (Corbicula fluminea).

Zebra mussels (Dreissena polymorpha) and Asian freshwater clams (Corbicula fluminea) are nonindigenous invasive bivalves present in North American fresh waters that are frequently contaminated with human enteric parasites, Cryptosporidium parvum and Giardia lamblia. Six-week laboratory exposure of D. polymorpha and Corbicula fluminea to both parasites seeded daily at concentrations reported from surface waters demonstrated efficient removal of Cryptosporidium parvum oocysts and G. lamblia cysts by both bivalve species. The number of parasites in mollusk tissue progressively increased in relation to the concentration of waterborne contamination, and decreased after cessation of the contamination. Oocysts outnumbered cysts in the tissue of both bivalves, and more parasites were identified in D. polymorpha than in Corbicula fluminea; overall 35.0% and 16.3% of the parasites seeded, respectively. Because C. fluminea and D. polymorpha can accumulate human waterborne parasites in proportion to ambient concentrations, these species of bivalves can be effective bioindicators of contamination of freshwater habitats with Cryptosporidium and Giardia.

Animals↗
PubMed2006

Effect of rSAG-1(P30) immunisation on the circulating and tissue parasites in guinea pigs as determined by quantitative PCR.

The efficacy of immunisation with Toxoplasma gondii recombinant protein (rSAG-1) was evaluated in the guinea pig model. For the infectious challenge, two strains, namely, strain C56 (10,000 tachyzoites) and strain 76K (100 cysts), were used to infect a group of 32 guinea pigs each. The circulating, cerebral and pulmonary parasite loads were determined with the real-time polymerase chain reaction (PCR) after immunisation. With the C56 strain, immunisation showed high activity with a reduction of greater than 1 log of the circulating and tissue parasite loads. Thus, there was a significantly lower circulating parasite load in the rSAG-1 + adjuvant group (0.5+/-1.5 Eq parasites/ml) as compared to that in the control group (67+/-110 Eq parasites/ml; p<0.05). In the same manner, the cerebral parasite load was much lower in the rSAG-1 + adjuvant group (10+/-20 Eq parasites/g) than that in the control group (339+/-291 Eq parasites/g; p<0.01). On the other hand, with the 76K strain, the effect of immunisation was much less and that only on the pulmonary parasite load [p(lung)<0.05]. This could be due to the use of different strains and stages of the parasite and/or the difference in the route of administration for challenge. The quantitative PCR technique used has shown a good correlation with animal inoculation, and when associated with the guinea pig model, it seems to be a useful and reproducible technique for future vaccine studies.

Adjuvants, Immunologic↗
PubMed2005

Plasmodium (Haemamoeba) cathemerium gene sequences for phylogenetic analysis of malaria parasites.

The DNA sequence information on avian malaria parasites of the genus Plasmodium is quite limited. At present, sequences of only 6 out of 34 valid species are available. However, sequence data of avian malaria parasites are particularly important with regard to the resolution of the phylogenetic relationships of the most virulent human malaria agent, Plasmodium falciparum. The question as to whether P. falciparum originates from avian or from mammalian parasites would contribute to our understanding of its biology and would probably facilitate the interpretation of experimental results. To add to the body of molecular data, we sequenced three genes (cytochrome b, 18 SSU rRNA, caseinolytic protease C) of different organellar origin of one of the most widespread avian malaria parasites, Plasmodium (Haemamoeba) cathemerium, which once used to be an important laboratory in vivo model in human malaria research. The analysis of the new P. cathemerium sequences in direct comparison with the rodent parasite P. berghei and the four human malaria parasites by pairwise distance calculation do not suggest a closer relationship of P. cathemerium to P. falciparum than to the other species involved.

Animals↗
PubMed2001

Parasite-specific antibody and cellular immune responses in human infected with Necator americanus and Oesophagostomum bifurcum.

In this study parasite-specific antibody, cellular reactivity and Thl-type or Th2-type cytokine responses were investigated in humans concurrently infected with Necator americanus and Oesophagostomum bifurcum. The prospects for O. bifurcum-specific serodiagnosis based on IgG4 and IgE were evaluated. IgG4 showed low specificity for O. bifurcum due to antigen cross-reactivity with N. americanus, while IgE specifically distinguished between hookworm and O. bifurcum, and, in doubly infected patients, levels of O. bifurcum-specific as well as N. americanus-specific IgE were significantly elevated compared to those with N. americanus mono-infections. Cellular immunity was not strictly dominated by a Thl- or Th2- type reactivity. In co-infected patients cellular unresponsiveness to parasite antigens was observed, while cellular production of tumour necrosis factor alpha (TNF-alpha) and gamma-interferon (IFN-gamma) was greater in those doubly infected. Th2-type cytokines (interleukin-5 and interleukin-10) were produced in equal amounts by peripheral blood mononuclear cells from individuals with mono- and coinfections. Such mixed Thl-type and Th2-type immune responsiveness associated with persisting gastrointestinal parasitic nematodes may reflect a state of infection at which parasite-induced inflammatory and enteropathogenic responses co-exist, and furthermore, helminth coinfection will not only suppress parasite-specific cellular responsiveness but may also direct cytokine production towards a "permissive Th1-type cytokine profile" that favours parasite persistence.

Adolescent↗
PubMed2005

Plant population size and isolation affect herbivory of Silene latifolia by the specialist herbivore Hadena bicruris and parasitism of the herbivore by parasitoids.

Habitat fragmentation can affect levels of herbivory in plant populations if plants and herbivores are differentially affected by fragmentation. Moreover, if herbivores are top-down controlled by predators or parasitoids, herbivory may also be affected by differential effects of fragmentation on herbivores and their natural enemies. We used natural Silene latifolia populations to examine the effects of plant population size and isolation on the level of herbivory by the seed predating noctuid Hadena bicruris and the rate of parasitism of the herbivore by its parasitoids. In addition, we examined oviposition rate, herbivory and parasitism in differently sized experimental populations. In natural populations, the level of herbivory increased and the rate of parasitism decreased with decreasing plant population size and increasing degree of isolation. The number of parasitoid species also declined with decreasing plant population size. In the experimental populations, the level of herbivory was also higher in smaller populations, in accordance with higher oviposition rates, but was not accompanied by lower rates of parasitism. Similarly, oviposition rate and herbivory, but not parasitism rate, increased near the edges of populations. These results suggests that in this system with the well dispersing herbivore H. bicruris, habitat fragmentation increases herbivory of the plant through a behavioural response of the moth that leads to higher oviposition rates in fragmented populations with a reduced population size, increased isolation and higher edge-to-interior ratio. Although the rate of parasitism and the number of parasitoid species declined with decreasing population size in the natural populations, we argue that in this system it is unlikely that this decline made a major contribution to increased herbivory.

Animals↗
PubMed2006

Brood parasitism increases provisioning rate, and reduces offspring recruitment and adult return rates, in a cowbird host.

Interspecific brood parasitism in birds presents a special problem for the host because the parasitic offspring exploit their foster parents, causing them to invest more energy in their current reproductive effort. Nestling brown-headed cowbirds (Molothrus ater) are a burden to relatively small hosts and may reduce fledgling quality and adult survival. We documented food-provisioning rates of one small host, the prothonotary warbler (Protonotaria citrea), at broods that were similar in age (containing nestlings 8-9 days old), but that varied in composition (number of warbler and cowbird nestlings) and mass, and measured the effect of brood parasitism on offspring recruitment and adult returns in the host. The rate of food provisioning increased with brood mass, and males and females contributed equally to feeding nestlings. Controlling for brood mass, the provisioning rate was higher for nests with cowbirds than those without. Recruitment of warbler fledglings from unparasitized nests was 1.6 and 3.7 times higher than that of fledglings from nests containing one or two cowbirds, respectively. Returns of double-brooded adult male and female warblers decreased with an increase in the number of cowbirds raised, but the decrease was more pronounced in males. Reduced returns of warbler adults and recruitment of warbler fledglings with increased cowbird parasitism was likely a result of reduced survival. Cowbird parasitism increased the warblers' investment in current reproductive effort, while exerting additional costs to current reproduction and residual reproductive value. Our study provides the strongest evidence to date for negative effects of cowbird parasitism on recruitment of host fledglings and survival of host adults.

Age Factors↗
PubMed2006

Pollination niche overlap between a parasitic plant and its host.

Niche theory predicts that species which share resources should evolve strategies to minimise competition for those resources, or the less competitive species would be extirpated. Some plant species are constrained to co-occur, for example parasitic plants and their hosts, and may overlap in their pollination niche if they flower at the same time and attract the same pollinators. Using field observations and experiments between 1996 and 2006, we tested a series of hypotheses regarding pollination niche overlap between a specialist parasitic plant Orobanche elatior (Orobanchaceae) and its host Centaurea scabiosa (Asteraceae). These species flower more or less at the same time, with some year-to-year variation. The host is pollinated by a diverse range of insects, which vary in their effectiveness, whilst the parasite is pollinated by a single species of bumblebee, Bombus pascuorum, which is also an effective pollinator of the host plant. The two species therefore have partially overlapping pollination niches. These niches are not finely subdivided by differential pollen placement, or by diurnal segregation of the niches. We therefore found no evidence of character displacement within the pollination niches of these species, possibly because pollinators are not a limiting resource for these plants. Direct observation of pollinator movements, coupled with experimental manipulations of host plant inflorescence density, showed that Bombus pascuorum only rarely moves between inflorescences of the host and the parasite and therefore the presence of one plant is unlikely to be facilitating pollination in the other. This is the first detailed examination of pollination niche overlap in a plant parasite system and we suggest avenues for future research in relation to pollination and other shared interactions between parasitic plants and their hosts.

Animals↗
PubMed2001

Effect of oral washes on the diagnosis of Pneumocystis carinii pneumonia with a low parasite burden and on detection of organisms in subclinical infections.

This study was designed to assess the efficacy of using oral washes (OWs) to diagnose Pneumocystis carinii pneumonia (PCP) in patients with a low parasite burden and to detect cases of subclinical infection. A total of 104 paired induced sputum (IS) samples and OWs from 104 HIV-seropositive patients and 32 OWs from immunocompetent healthy controls were studied. All of the control samples were negative. Fifty-two IS specimens were positive for Pneumocystis carinii, and 26 of these cases were also detected in the OWs using conventional stain or polymerase chain reaction. Twenty-four of the PCP cases had a high or a moderate parasite load and 28 had a low parasite load; among them, Pneumocystis carinii was detected in the OWs of 15 and 11 cases, respectively. Fifteen of the 104 IS samples studied belonged to patients who were asymptomatic carriers or who had a subclinical infection, and Pneumocystis carinii was detected in the OWs of 4 of these cases. The parasite was not detected in 37 IS samples and in 74 OWs. The results of this study indicate that in patients with a low pulmonary parasite burden, the number of organisms reaching the oral cavity is insufficient for reliable detection in OWs. Thus, OWs are less useful than IS samples for detecting Pneumocystis carinii in cases of pneumonia in which a low parasite burden and/or subclinical infection are present.

AIDS-Related Opportunistic Infections↗
PubMed1987

Schistosoma mansoni: migration potential of normal and radiation attenuated parasites in naive guinea pigs.

Compressed tissue autoradiography using [75Se]selenomethionine labelled parasites has been used to investigate the migration potential of normal and radiation attenuated cercariae of Schistosoma mansoni in naive guinea pigs. By Day 14 after infection. 44% of normal parasites were detected as reduced silver foci in the liver; this value corresponded well with the number of liver parasites recovered by retrograde perfusion of the hepatic portal system on Day 42 (42% of the challenge). In contrast, cercariae subjected to 50 krad of gamma irradiation failed to migrate out of the skin. The migration capacity of 20 krad irradiated parasites was less severely affected in that about half of the challenge parasites reached the lungs, but virtually none moved to the liver. These data are discussed in relation to the kinetics of immunity induced in guinea pigs by infection or vaccination with normal or radiation attenuated parasites.

Animals↗