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PubMed2005

Parasite species coexistence and limiting similarity: a multiscale look at phylogenetic, functional and reproductive distances.

The factors that control biodiversity have been the focus of numerous recent investigations; these include species interactions, speciation, environmental gradients and heterogeneity, all of these operating differently at each observation scale. We used a null model to examine the influence of two forces shaping the community structure of Dactylogyrus species parasitic on roach (Rutilus rutilus) gills: interspecific competition that might prevent the coexistence of the most similar species and environmental filters that might result in the most similar species coexisting together. The study was carried out on two sets of fish from two different localities in the Morava river basin (Czech Republic) to evaluate the consistency of the results across host populations, and at three different scales of observation to test for the scale dependence of assembly rules. In decreasing order, from largest to smallest, the three spatial scales investigated were: the individual fish, the individual gill arch and individual sections of each gill arch. The similarity between pairs of parasite species was measured using three different criteria: (1) phylogeny, (2) quantitative functional traits consisting of parasite size and morphometric measurements of the attachment organ's sclerotized parts and (3) qualitative attributes of reproductive organs. First, our study reveals a strong conservatism of ecological characters for the nine Dactylogyrus parasite species, in particular regarding the attributes of their copulatory organs. Second, our study did not find any limitation of similarity among coexisting Dactylogyrus species due to interspecific competition, irrespective of the scale and the similarity measures considered. Conversely, our results support the niche filtering hypothesis, preventing the co-occurrence of species too dissimilar from one another. This process is particularly apparent at the scale of the individual fish and for functional traits associated with the hard parts of the parasites' attachment organs. In both localities, the Dactylogyrus species that occur on the same fish individuals tend to have similar values for the haptor dimensions. Our study supports previous studies on monogenean parasite communities indicating a weak influence of competition as a structuring force, but it goes a step further by identifying environmental filtering as a key process shaping these communities.

Animals↗
PubMed2006

Persistence of host and parasite populations subject to experimental size-selective removal.

Predators have the potential to limit the spread of pathogens not only by selecting infected prey but also by shaping prey demographics. We tested this idea with an epidemiological experiment in which we simulated variable levels of size-selective predation on zooplankton hosts and monitored the persistence of host and parasite populations. In the absence of simulated predation, the virulent protozoan Caullerya mesnili frequently drove its host Daphnia galeata to extinction. Uninfected control populations showed lower extinction rates and higher average densities than infected populations in the absence of simulated predation (all of the latter went extinct or remained infected). With a weak removal rate of the largest hosts, the proportion of populations in which the parasite drove the host to extinction decreased, while the number of populations in which the host persisted and the parasite went extinct increased. Host-parasite coexistence was also observed in some cases. With intermediate levels of removal, most of the parasite populations went extinct, while the host populations persisted. With an even higher removal rate, Daphnia were driven to extinction as well. Thus, variation in one factor, size-selective mortality, resulted in four different patterns of population dynamics. Our results highlight the potential role of predation in shaping the epidemiology and community structure of host-parasite systems.

Animals↗
PubMed1990

Marine parasites: an Australian perspective.

A review is given of major studies in marine parasitology in Australia. Aspects discussed include: geographical distribution of parasites in Australian coastal waters and their affinities to parasites of other zoogeographical regions; species diversity in Australian coastal surface and deep waters; use of marine parasites for stock discrimination; use of marine parasites as ecological models; ultrastructural and phylogenetic studies of marine parasites; and effects of marine parasites on their hosts.

Animals↗
PubMed1993

Insemination and population density in Entobdella soleae, a monogenean skin parasite of the common sole, Solea solea.

Immature specimens of the monogenean skin parasite Entobdella soleae, experimentally isolated from other individuals, fail to self-inseminate when maturity is reached and self-insemination has not been recognized during many hours spent observing living parasites. E. soleae lives on the lower surface of its flatfish host, the common sole (Solea solea), in relatively small numbers, most commonly 1, 2 or 3 adults per fish, but in spite of the low density and extensive habitat, freshly collected wild parasites were found to be inseminated. If it is assumed that E. soleae is unable to self-inseminate in the wild, then it seems likely that single isolated parasites on wild soles have lost their partners as a result of death or transfer to another host and that parasites have an efficient way of locating a mating partner. Mathematical modelling indicates that random locomotion with searching movements of the body would lead to mating contacts between 2 individuals on a small sole within the reproductive life-time of the parasites, but is unlikely to maximize reproductive output because it cannot ensure that mating will occur soon after sexual maturity is achieved. It is suggested that pheromonal attraction may ensure early meetings and that the thin stagnant layer of sea water between the lower surface of the relatively inactive sole and the sea bottom is an ideal environment for the operation of such a system and may account for the preference of adult E. soleae for the host's lower surface.

Animals↗
PubMedDate not supplied

Immunogenetic and evolutionary influences on the host-parasite relationship.

Immunogenetic aspects of the host-parasite relationship between the laboratory mouse and the parasitic nematode Trichinella spiralis are reviewed. Variation in the capacity of hosts to express an effective protective immunity is associated primarily with variation in inflammatory responsiveness. Analysis of the contributions of T lymphocytes, cytokines, and myeloid precursor populations to variation in one particular inflammatory component, eosinophilia, is described. Variation in parasite immunogenicity at the level of host responsiveness to different parasite isolates is described briefly. Variations in host-protective immunity, immunopathology, and parasite immunogenicity are discussed in terms of evolutionary pressures selecting for optimal host and parasite survival in a stable symbiosis.

Animals↗
PubMed1987

The interaction of a Trypanosoma cruzi surface protein with Vero cells and its relationship with parasite adhesion.

Previous studies have shown that adhesion to fibroblastic cells of cell culture-derived trypomastigotes of Trypanosoma cruzi probably occurs through a ligand-receptor interaction. The results now obtained indicate that solubilization with a mild detergent ('Chaps', 0.8%) of 125I-surface proteins of trypomastigotes, followed by detergent removal and interaction of the solubilized proteins with a monolayer of intact Vero cells, brings about binding to the cells of a parasite surface protein, which exhibits a molecular weight of 83,000 and isoelectric point of 8.1-8.6 upon two-dimensional polyacrylamide gel electrophoresis. This polypeptide was detected in extracts of highly adherent, extracellularly incubated parasites, but not in extracts of poorly adhesive, recently released trypomastigotes. The detergent-free extracts of incubated trypomastigotes inhibit attachment of live parasites to Vero cells, while extracts of fresh trypomastigotes are nearly ineffective. Binding of the parasite polypeptide to the cells is stimulated by parasite trypsinization or activation in the presence of tunicamycin, and it is inhibited by the presence of mannan or by Vero cell trypsinization, thus showing a similar behaviour to that observed for parasite attachment to Vero cells under these conditions. These results suggest that the surface membranes of activated, highly adherent T. cruzi trypomastigotes contain an 83 kDa polypeptide which acts as a lectin-like protein that can interact with the surface of Vero fibroblasts, probably through mannose residues of a glycoprotein receptor of the host cell.

Adhesiveness↗
PubMed1984

The economics of parasitic diseases: research priorities.

Parasitic diseases are primarily diseases of poverty. At serious risk are individuals, communities and countries least able to afford the costs of treatment or prevention. In turn, economic development projects which aim to increase income levels may lead to negative results because of increased transmission of parasitic diseases often results. In attempting to analyse the economic consequences of parasitic diseases and the economics of their control, economists have usually relied on the tools of cost-benefit analysis, cost-effectiveness analysis and financial analysis. These efforts are briefly reviewed in the paper. The results have been subject to considerable criticism because of conceptual and methodological problems. For example, most studies have not taken into account the epidemiology and natural history of the disease in estimating the associated economic losses, thereby leading to inappropriate conclusions. The UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases through its Social and Economic Research Scientific Working Group (SER-SWG) is promoting research on the economics of parasitic diseases. In an attempt to improve the usefulness and reliability of such studies, conceptual and methodological approaches have been suggested which are reported on here. To improve the research design of these projects, a conceptual framework is proposed which consists of four components: (1) baseline social, cultural and economic conditions influencing disease transmission; (2) resources already invested in the health system and investments in other related sectors such as agriculture, housing, water supply and sanitation; (3) health consequences resulting from (1) and (2); and (4) social and economic consequences resulting from (3). A key concern in relation to the framework is to determine the most useful basis for linking results from studies of one component to another so as to analyse more systematically the impacts of disease on individuals and society. Such studies are inherently interdisciplinary and close collaboration of economists with medical scientists and disease control programme staff is needed to ensure completeness and reliability of input data and results. Results from these studies could be used to inform national decision-makers about the social and economic consequences of the parasitic diseases and their control and, thus, should strengthen support for increased investment to reduce the parasitic disease burden in developing countries.

Communicable Disease Control↗
PubMed2005

Host regulation and release of parasitism-specific proteins in the system Toxoneuron nigriceps-Heliothis virescens.

The braconid wasp Toxoneuron nigriceps induced qualitative and quantitative changes in the protein composition of the moth Heliothis virescens host hemolymph. Total protein concentration was found to be higher in parasitized host 4 days after parasitism as compared to control hosts, mainly due to changes in a particular group of proteins. Host proteins with a molecular mass of 173 and 72 kDa were found in higher levels in the hemolymph of parasitized larvae as control hosts approached pupation, while an 80 kDa peptide was found in reduced concentration in the hemolymph of parasitized hosts. Levels of these three peptides were maintained throughout parasitoid development, while two of them (173 and 72 kDa) were cleared from the host hemolymph close to pupation. Besides the regulation of host proteins, three parasitism-specific proteins (PSPs) were released into the host hemolymph. Two of them (PSP1-MW=116 kDa, pI=6.3; PSP2-MW=114 kDa, pI=6.2) first appeared in the hemolymph of parasitized hosts soon after pupation of control host and increased in concentration as the parasitoid developed. The third PSP (PSP3-MW=56 kDa, pI=5.8) was produced towards the end of parasitoid larval development, close to parasitoid egression. Database searches based on the amino acid composition and amino terminal sequence of PSP1 and PSP2 did not produce any significant matches, while PSP3 was identified as a putative chitinase. Incubation of host derived tissues, parasitoid larvae and teratocytes in 35S conditioned media suggested PSPs were a product of teratocytes. The role of the regulation of host proteins and release of PSPs by teratocytes for the successful development of T. nigriceps are discussed.

Amino Acid Sequence↗
PubMed2006

Quantitative isolation and in vivo imaging of malaria parasite liver stages.

The liver stages of Plasmodium, the causative agent of malaria, are the least explored forms in the parasite's life cycle despite their recognition as key vaccine and drug targets. In vivo experimental access to liver stages of human malaria parasites is practically prohibited and therefore rodent model malaria parasites have been used for in vivo studies. However, even in rodent models progress in the analysis of liver stages has been limited, mainly due to their low abundance and associated difficulties in visualisation and isolation. Here, we present green fluorescent protein (GFP)-tagged Plasmodium yoelii rodent malaria parasite liver infections in BALB/c mice as an excellent quantitative model for the live visualisation and isolation of the so far elusive liver stages. We believe P. yoelii GFP-tagged liver stages allow, for the first time, the efficient quantitative isolation of intact early and late liver stage-infected hepatocyte units by fluorescence activated cell sorting. GFP-tagged liver stages are also well suited for intravital imaging, allowing us for the first time to visualise them in real time. We identify previously unrecognised features of liver stages including vigorous parasite movement and expulsion of 'extrusomes'. Intravital imaging thus reveals new, important information on the malaria parasite's transition from tissue to blood stage.

Animals↗
PubMed2005

Parasitization of Manduca sexta larvae by the parasitoid wasp Cotesia congregata induces an impaired host immune response.

During oviposition, the parasitoid wasp Cotesia congregata injects polydnavirus, venom, and parasitoid eggs into larvae of its lepidopteran host, the tobacco hornworm, Manduca sexta. Polydnaviruses (PDVs) suppress the immune system of the host and allow the juvenile parasitoids to develop without being encapsulated by host hemocytes mobilized by the immune system. Previous work identified a gene in the Cotesia rubecula PDV (CrV1) that is responsible for depolymerization of actin in hemocytes of the host Pieris rapae during a narrow temporal window from 4 to 8h post-parasitization. Its expression appears temporally correlated with hemocyte dysfunction. After this time, the hemocytes recover, and encapsulation is then inhibited by other mechanism(s). In contrast, in parasitized tobacco hornworm larvae this type of inactivation in hemocytes of parasitized M. sexta larvae leads to irreversible cellular disruption. We have characterized the temporal pattern of expression of the CrV1-homolog from the C. congregata PDV in host fat body and hemocytes using Northern blots, and localized the protein in host hemocytes with polyclonal antibodies to CrV1 protein produced in P. rapae in response to expression of the CrV1 protein. Host hemocytes stained with FITC-labeled phalloidin, which binds to filamentous actin, were used to observe hemocyte disruption in parasitized and virus-injected hosts and a comparison was made to hemocytes of nonparasitized control larvae. At 24h post-parasitization host hemocytes were significantly altered compared to those of nonparasitized larvae. Hemocytes from newly parasitized hosts displayed blebbing, inhibition of spreading and adhesion, and overall cell disruption. A CrV1-homolog gene product was localized in host hemocytes using polyclonal CrV1 antibodies, suggesting that CrV1-like gene products of C. congregata's bracovirus are responsible for the impaired immune response of the host.

Animals↗
PubMed2005

In vivo imaging of malaria parasites--recent advances and future directions.

A new view into the life of malaria parasites is now possible owing to recent advances in imaging techniques and to the generation of tagged parasites. Insights into how parasites interact with their insect vectors and mammalian hosts have been gained by the study of various parasitic forms in their natural environment. Quantitative analysis of Plasmodium ookinete motility has revealed different modes of motility in parasite invasion of the mosquito gut and the extrusion of invaded gut cells from the epithelium. Similar analysis with Plasmodium sporozoites has revealed the importance of parasite motility in transmission from the mosquito vector to the mammalian host.

Animals↗
PubMed2006

Inflammatory lesion and parasite load are inversely associated in Leishmania amazonensis infected mice genetically selected according to oral tolerance susceptibility.

Two strains of mice selected according to extreme phenotypes of susceptibility and resistance to oral tolerance (TS and TR mice, respectively) were infected with 1 x 10(7) Leishmania amazonensis promastigotes and studied comparatively. TS mice developed a minor pathology while permitting parasite growth with the presence of increased IL-4, IL-10 and IFN-gamma, and lower NO and IL-2 levels and delayed-type hypersensitivity (DTH). In contrast, in TR mice, footpad swelling was increased but parasite growth was reduced. They produced lower IL-4, IL-10 and IFN-gamma but increased NO, IL-2 levels, DTH, activated spleen macrophages and periarteriolar lymphoid sheaths. The results suggest that the tolerogenic TS mouse profile, with higher IL-10 production, impaired lesion development but also avoided macrophage leishmanicidal activity, maintaining in this manner a silent parasite load. On the other hand, the TR mouse profile contributed to lesion progression with controlled parasite load. To directly address the influence of oral tolerance on infection, mice were gavaged with OVA, and 7 days afterwards were infected and challenged to bystander suppression with OVA in the same footpad. In TR mice gavaged with 25 mg OVA the inflammatory lesion was largely enhanced, while with 5 mg OVA the lesion was diminished. In TS mice the footpad swelling was always lower. However, the bystander effect did not modify the establishment of infection; and similarly to the control non-bystander mice, parasite clearance was maintained in TR and prevented in TS mice. Therefore, a better comprehension of immunoregulation of innate and adaptive immunity in the early stages of infection is necessary for the development of protocols preventing inflammation and contributing to the elimination of parasites.

Administration, Oral↗
PubMed2004

The role of Steinernema feltiae body-surface lipids in host-parasite immunological interactions.

Interactions between entomopathogenic nematodes (Steinernema feltiae) and insect host (Galleria mellonella) immune system were investigated. We focused on the immunosuppressive properties of the parasite cuticle and on its interaction with hemolymph humoral components. Effects of parasite cuticle against host proPO system enzymatic cascade were evaluated a short time after infection. The presence of parasite cuticles decreased both normal and LPS-elicited proPO system activity, suggesting that S. feltiae body surface plays a key role in the early parasitation phase, probably interfering with host proPO activation pathways. The data obtained showed that cuticle lipidic compounds are able to interact with host humoral components, removing them from the hemolymph. The depletion of these molecules, arbitrarily named host-interacting proteins (HIPs), seems to be responsible of the drastic decrease in proPO system activity. Moreover, hemolymph HIPs showed LPS-binding properties and parasite cuticle cross-reacted with anti-LPS antibodies. Finally, we also assessed the involvement of parasite body surface on immunoevasion strategies of S. feltiae against host cell-mediated encapsulation processes. We conclude that S. feltiae body surface is responsible for short-term immunosuppression and immunoevasion processes; since it is able to sequester host hemolymph compounds involved in proPO system activation and this process could be responsible for a molecular disguise strategy against cellular encapsulation.

Animals↗
PubMed2004

Role of calreticulin from parasites in its interaction with vertebrate hosts.

Although parasites range from protozoan to complex, evolutionary advanced arthropods, in general, a hallmark of parasite life cycles is their ability to adapt to changes in temperature, pH and host defense strategies. Calreticulin, a calcium-binding protein, highly conserved and multifunctional, is present in every cell of higher organisms, except erythrocytes. The surprising array of calreticulin-associated functions include lectin-like chaperoning, calcium storage and signaling, modulation of gene expression, cell adhesion, enhancement of phagocytosis of C1q or collectin opsonized apoptotic cells, inhibition of angiogenesis and tumoral growth, inhibition of perforin pore formation in T and NK cells, and inhibition of C1q-dependent complement activation. Likewise, calreticulin is present in a wide spectrum of sub cellular compartments. Parasite calreticulin shows a surprisingly high degree of conservation within the framework of its functional domains. Its role within the parasite/host relationship needs to be assessed further, in particular with regard to its impact on parasite infectivity, by helping to evade from its hosts' immune response. With special emphasis on calreticulin from Trypanosoma cruzi, the intracellular protozoan agent of American trypanosomiasis (Chagas' disease), we wish to exemplify and highlight the various implications of parasite calreticulin, within the pathophysiology of parasite-mediated human and animal disease.

Animals↗
PubMed2003

Benzimidazole-resistant beta-tubulin alleles in a population of parasitic nematodes (Cooperia oncophora) of cattle.

Three anthelmintic classes with distinct mechanisms of action are commercially available. Selection of nematode populations resistant to all these drugs has occurred, particularly in trichostrongyloid parasites of sheep. Anthelmintic resistance in cattle parasites has only recently been recognized and appears to be less pronounced, even though very similar species infect both hosts. To understand the bases for differences in the rate of resistance development in sheep versus cattle parasites, it is important to first demonstrate that the same kinds of resistance alleles exist in both. The benzimidazoles (BZ), which have been used for more than 40 years, were chosen as an example. BZ-sensitive (BZ(S)) and BZ-resistant (BZ(R)) nematodes that parasitize sheep have been distinguished at the molecular level by a single nucleotide change in the codon for amino acid 200 of a beta-tubulin gene, a switch from TTC (phenylalanine) to TAC (tyrosine). PCR primers were designed to completely conserved regions of trichostrongyloid beta-tubulin genes and were used to amplify DNA fragments from Haemonchus contortus (cDNA from a BZ(S) and a BZ(R) library) as positive controls. The technique was then extended to the cattle parasites, Cooperia oncophora and Ostertagia ostertagi (from genomic DNA). Sequence analysis proved the presence of amplified BZ(S) alleles in all three species and BZ(R) alleles in the BZ(R) population of H. contortus. Based on these data, nested PCR primers using the diagnostic T or A as the most 3' nucleotide were designed for each species. Conditions for selective PCR were determined. To demonstrate feasibility, genomic DNA was recovered from individual H. contortus L(3) larvae from both BZ(S) and BZ(R) populations. Genomic DNA was also isolated from >70 individual adult male C. oncophora collected from a cattle farm in New Zealand with reported BZ resistance. Allele-specific PCR discriminated among heterozygotes and homozygotes in both species. This method could find utility in studying the molecular epidemiology of BZ resistance in cattle parasites and for defining the variables that limit the development and spread of anthelmintic resistance in this host.

Alleles↗
PubMed2004

Phylogeny of Lasius ants based on mitochondrial DNA and morphology, and the evolution of social parasitism in the Lasiini (Hymenoptera: Formicidae).

Phylogeny of ants of the tribe Lasiini (Lasius, Acanthomyops, Prenolepis, Euprenolepis, Paratrechina, Pseudolasius, and Myrmecocystus) was analysed using 81 morphological, ecological, and behavioural characters (for 41 species) and mitochondrial DNA sequences (COI, COII, tRNA-Leu; for 19 species). The free-living subgenus Lasius s. str. is paraphyletic with respect to the rest of genus; the traditional "genus" Acanthomyops should be considered a part of Lasius s. lat.; free-living subgenus Cautolasius is a member of the clade of socially parasitic Lasius ants (=Chtonolasius+Acanthomyops+Austrolasius+Dendrolasius). The tree topology is congruent with two alternative scenarios of origin of the temporary social parasitism: (i) a single origin of the parasitic strategy in a derived subclade of Lasius and a secondary loss of this trait in Cautolasius, (ii) a parallel origin of the social parasitism within the clade of hypogeic Lasius ants (in Chtonolasius, and in Acanthomyops+Dendrolasius+Austrolasius). Emery's rule in the strict sense does not apply to this group because most parasites exploit any ecologically available, even phylogenetically distant host species. The parasitic strategy in Lasius could have originated from the aggressive interactions between cofounding queens during pleometric colony founding and/or from the secondary queen adoption.

Animals↗
PubMed1998

Some gastro-intestinal parasites of zoonotic (public health) importance commonly observed in old world non-human primates in Kenya.

A study was undertaken to categorise some gastro-intestinal (GIT) parasites commonly observed in Kenyan non-human primates (NHPs) on the basis of their health implications for humans. Six species of locally available non-human primates, namely olive baboons (Papio cyanocephalus anubis), Vervet monkey (Cercopithecus aethiops), Sykes monkey (Cercopithecus mitis), Black and white colobus (Colobus abyssinicus), Debrazzas monkey (Cercopithecus neglectus) and Grey and Black mangabeys (Cercocebus torquatus and Cercocebus albigena) which were imported from Zaire (Democratic Republic of Congo) were sampled. Simple laboratory methods involving microscopic examination of stained faecal smears were used. Wet faecal smears stained with iodine and unstained controls were used for conventional parasites while acid fast staining was employed to detect Cryptosporidium oocysts. Both helminths and protozoan parasites were detected in varying rates in all primate species. Trichuris sp. was the most frequent helminth followed by Strongyloides fulleborni, Strongyles sp. and Schistosoma mansoni in that order. Entamoeba coli was the most common protozoan followed, respectively, by Balantidiun coli and Entamoeba histolytica. All primate species examined were infected with all the parasites listed except the black and white colobus. Cryptosporidium was found in both clinically normal and diarrhoeic baboons and vervets. Most taxa of parasites observed could prejudice human welfare directly through infection and causation of illness and indirectly through increased cost of livestock production and decreased availability of animal proteins. The potential of some of the agents to cause opportunistic infections in immuno-compromised persons was suggested as a likely threat to man's well-being. This would warrant such person's exemption from high risk operations at primate and other animal facilities in developing countries. Further, specific studies are needed to provide data on the epidemiology, socio-economic impact and pathogenicity of the primate parasites to other species of animals and man.

Animals↗
PubMed2002

Vampires, Pasteur and reactive oxygen species. Is the switch from aerobic to anaerobic metabolism a preventive antioxidant defence in blood-feeding parasites?

Several species of parasites show a reduction of their respiratory activity along their developmental cycles after they start to feed on vertebrate blood, relying on anaerobic degradation of carbohydrates to achieve their energy requirements. Usually, these parasites choose not to breathe despite of living in an environment of high oxygen availability such as vertebrate blood. Absence of the 'Pasteur effect' in most of these parasites has been well documented. Interestingly, together with the switch from aerobic to anaerobic metabolism in these parasites, there is clear evidence pointing to an increase in their antioxidant defences. As the respiratory chain in mitochondria is a major site of production of reactive oxygen species (ROS), we propose here that the arrest of respiration constitutes an adaptation to avoid the toxic effects of ROS. This situation would be especially critical for blood-feeding parasites because ROS produced in mitochondria would interact with pro-oxidant products of blood digestion, such as haem and/or iron, and increase the oxidative damage to the parasite's cells.

Anaerobiosis↗