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At least 109 records · Page 6Linked to original sources
PubMed2003

The effect of birdsfoot trefoil (Lotus corniculatus) and chicory (Cichorium intybus) on parasite intensities and performance of lambs naturally infected with helminth parasites.

Conventionally, farmers rely upon the routine use of anthelmintics to control helminth parasites and their use has proved highly cost-effective. However, several factors, including the emergence of helminths resistant to pharmaceutical anthelmintics, are forcing farmers to seek alternative approaches to parasite control. Studies in New Zealand have shown that some alternative forages may reduce parasitic infestation in sheep. In the current study, it was found that under UK environmental conditions lambs with naturally acquired helminth infections grazing chicory (Cichorium intybus) and birdsfoot trefoil (Lotus corniculatus) had fewer helminth parasites than sheep grazing ryegrass/white clover (Lolium perenne/Trifolium repens). Twelve pure-bred Lleyn male lambs grazed replicated 0.5ha plots of birdsfoot trefoil, chicory or ryegrass/white clover for 5 weeks. Liveweight and faecal egg counts (FECs) were determined weekly and eight lambs per forage were slaughtered at the end of the trial to determine total helminth intensities. Lambs grazing birdsfoot trefoil had a lower FEC on day 7 (P<0.05) and fewer total adult helminths than those grazing the other forages on day 35 (P<0.01). Lambs grazing chicory did not have significantly lower FEC than lambs grazing other forages but these lambs were found to have fewer total adult abomasal helminths than lambs grazing ryegrass/white clover (P<0.001). As the performance of grazing lambs is inversely correlated with the intensity of helminth parasites, these alternative forages could be used to improve the liveweight gain of lambs produced in the UK. Overall, the results support the contention that alternative forages could have a positive role in the control of helminth parasites in sheep, subject to successful agronomic development and integration of these forages into whole farm systems.

Abomasum↗
PubMed2000

Trypanosoma cruzi infection and the rat central nervous system: proliferation of parasites in astrocytes and the brain reaction to parasitism.

Chagas' disease, caused by the protozoan Trypanosoma cruzi, is characterized by an acute phase in which parasites circulate in the blood and proliferate in several cell types, especially muscle cells. A life-long chronic phase follows the acute phase. In young patients, the acute phase is more severe, and meningoencephalitis frequently occurs in children before 2 years of age. Parasites have been rarely observed in neurons but their presence inside glial cells has been reported without characterization of the glial cell type. The cells involved in the brain reaction to the parasites and the time course of this reaction remain to be studied. Therefore, using suckling and juvenile rats and different T. cruzi populations, we aimed at determining the brain target for parasite proliferation and the cells involved in the brain reaction. Around the middle of the acute phase, histological and ultrastructural findings indicated that T. cruzi proliferates in astrocytes, forming nests devoid of enclosing membrane as described for non-glial cells. The brain nodular reaction comprised astrocytes, microglia, macrophages and neutrophils. Resting microglia was devoid of parasites in contrast to macrophages and neutrophils that probably participate in parasite removal. Suckling animals were significantly more affected, the numbers of nests and nodules varying with inoculum size. Histoquantitative analysis showed higher number of nests at the parasitemic peak (day 13) and drastic fall at day 20 post-inoculation. The highest number of nodules occurred at day 20 with drastic reduction at day 30. Recovery from histopathological alterations occurred even in surviving younger animals.

Age Factors↗
PubMed2001

The role of mucins in host-parasite interactions: Part II - helminth parasites.

Some parasites express mucin-like molecules. These have possible roles in attachment and invasion of host cells and in the avoidance of host immune processes. Enzymes of parasite origin might also facilitate infection, either by degrading host mucus barriers or by generating binding sites on host cells. Host mucins have roles in preventing parasite establishment or in parasite expulsion. They, in turn, might be exploited by parasites, either as sources of fuel or binding sites, or as host-finding targets. Here, we describe the biochemical properties of mucins and mucin-like molecules in relation to interactions (established and putative) between helminth parasites and their hosts.

Animals↗
PubMed2004

Parasite dose, prevalence of infection and local adaptation in a host-parasite system.

Parasites have been found to be more infective to sympatric hosts (local adaptation) in some systems but not in others. The variable nature of results might arise due to differences in host and/or parasite migration rates, parasite virulence, specificity of infection, and to differences in the dose-response functions. We tested this latter possibility by manipulating the dose of trematode (Microphallus sp.) eggs on sympatric and allopatric host populations (Potamopyrgus antipodarum). We found that infection rapidly increased to a high asymptote (0.88 +/- 0.02, 1 S.E.) in the sympatric host population, but infections were low and surprisingly unrelated to dose in the allopatric host. We also found that host survival and growth rate were not negatively affected by increasing parasite dose in either population. These results suggest that defences in the allopatric host were not overwhelmed at high parasite doses, and that any life-history costs of defence are not plastic responses to parasite dose.

Adaptation, Biological↗
PubMed1999

Richness and diversity of parasite communities in European eels Anguilla anguilla of the River Rhine, Germany, with special reference to helminth parasites.

A total of 121 European eels (Anguilla anguilla) from 2 sampling sites on the River Rhine were investigated in respect of their parasite communities. Special attention was given to the swim bladders, intestines, gills and fins of the fish. Twelve different parasite species were found to live in and on the eels. Data from each sampling site were kept separate. Parasites found in descending order of prevalence were: Anguillicola crassus, Trypanosoma granulosum, Myxobolus sp., Paratenuisentis ambiguus, Pseudodactylogyrus sp., Bothriocephalus claviceps, Myxidium giardi, Pomphorhynchus laevis, Trichodina sp., Raphidascaris acus, Acanthocephalus lucii and Acanthocephalus anguillae. Significantly different prevalences were reported for L3 larvae of A. crassus, adult P. ambiguus, B. claviceps and Myxobolus sp. at the 2 sampling sites. The highest number of parasite species was recorded from the intestine, which contained up to 6 different helminths. The coexistence of the acanthocephalans P. laevis and P. ambiguus, which showed clear patterns of distribution within the intestine of the respective hosts, was reported for the first time. Up to 3 different helminth species were found in the intestine of individual fish. Among those, acanthocephalans were the most prevalent worms with the eel-specific parasite P. ambiguus as the dominant species not only of the intestinal but also of the total component communities. Both infra and component communities exhibited low diversity and were dominated by this single species. The evenness reached only approximately 50% or less and it remained unclear why the helminth communities of the eels from the River Rhine with its huge catchment area exhibit such a low parasite diversity and high dominance.

Air Sacs↗
PubMed1996

Parasite-host coevolution and geographic patterns of parasite infectivity and host susceptibility.

Ebert (1994) has proposed the rule that parasites are, with few exceptions, more infective to sympatric hosts than to allopatric hosts. We test this rule using field data for schistosome infections of planorbid snails and find that, although sympatric parasite-host combinations do tend to be more compatible, there are exceptions where particular allopatric parasite-host populations are significantly more compatible. We develop a mathematical model of the dynamics of the parasite-host interaction where parasite infectivity and host susceptibility are defined by the matching of genotypes in a diploid system, The model predicts dynamic polymorphisms where parasite allele frequencies track host allele frequencies but with a lag. Because of this lag, it is possible for allopatric combinations to be more compatible than sympatric combinations. Any 'rule' that precludes this possibility is unlikely to prove robust.

Alleles↗
PubMed1975

Parasite reproductive strategy and evolution of castration of hosts by parasites.

A modification of the Euler equation is used to describe a simple parasite life history in which survival decreases with age at a rate determined by mortality of the parasitized host. The advantages of castration of hosts by parasites are discussed using the modified equation in which castration is equivalent to reducing parasite virulence in the host to near zero or zero. It is suggested that castrating parasites can infest a wider range of hosts with higher mortality rates and that within parasite groups having castrating and noncastrating species, the former should infest hosts with higher mortality rates and relatively larger gonads.

Ecology↗
PubMed1999

Parasitism increases offspring size in a damselfly: experimental evidence for parasite-mediated maternal effects.

The effects of parasites on host fitness and the fitness effects of maternal effects are widely discussed. In this study, I conducted an experiment linking both aspects. I manipulated the ectoparasite load (Acari: Arrenurus cuspidator) of damselflies, Coenagrion puella, and found that larvae from mothers with high parasite loads were larger (assessed by head width) than larvae from mothers with low parasite loads. Furthermore, there was a negative correlation between the number of eggs laid and parasite load. Parasitized mothers thus seemed to have fewer, but probably better, offspring. The ecological significance of these parasite-mediated maternal effects remains to be tested. However, size-dependent cannibalism almost certainly has important consequences for population dynamics. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2003

Transmission dynamics of a trematode parasite: exposure, acquired resistance and parasite aggregation.

This paper examines the relative importance of exposure and susceptibility to the infection of rainbow trout ( Oncorhynchus mykiss) with the trematode parasite Diplostomum spathaceum under natural conditions. A total of 93 individually marked, similarly aged fish were introduced into three cages at regular time intervals and the intensity of infection in individuals recorded by counting parasites in live fish using ophthalmic techniques. Fish introduced into the cages became infected faster than fish that were already in the cages, indicating that fish developed resistance to infection after repeated exposure. Fish kept in the cages experienced similar levels of exposure and the distribution of parasites between these fish was not significantly different from a random distribution. In contrast, parasites from 16 Finnish wild roach populations were highly aggregated. The differences between the caged fish and the wild fish indicate that the aggregated distribution in wild fish might be determined by variations in exposure rather than variations in susceptibility between fish. This is one of the few studies to demonstrate the development of resistance in fish against the parasite under natural conditions, and to attempt to separate exposure and susceptibility as causative agents of parasite aggregation.

Animals↗
PubMedDate not supplied

Pasteuria thornei sp. nov. and Pasteuria penetrans sensu stricto emend., mycelial and endospore-forming bacteria parasitic, respectively, on plant-parasitic nematodes of the genera Pratylenchus and Meloidogyne.

Descriptions are presented of two members of the Pasteuria penetrans group of mycelial and endospore-forming bacteria, parasitic on plant-parasitic nematodes. In one case, the epithet P. penetrans sensu stricto emend. has now been limited to members of this group with cup-shaped sporangia and ellipsoidal endospores, parasitic primarily on the root-knot nematode Meloidogyne incognita. The second organism, with rhomboidal sporangia and nearly spherical endospores, which is parasitic primarily on the root-lesion nematode Pratylenchus brachyurus, is assigned to P. thornei sp. nov. An updated and emended description is offered of the genus Pasteuria Metchnikoff 1888 emend. The relationships are analysed among these two nematode parasites and the type species of this genus, P. ramosa Metchnikoff 1888, a parasite of cladoceran invertebrates. Because none of these microbes has been publicly reported to have been cultivated axenically, these relationships are based mainly on morphological, developmental, and pathological criteria.

Animals↗
PubMed1997

Parasitism-induced Effects on Host Growth and Metabolic Efficiency in Tobacco Hornworm Larvae Parasitized by Cotesia congregata.

Parasitism by the braconid wasp Cotesia congregata affects the growth of Manduca sexta larvae in a parasitoid 'dose-dependent' fashion. Following parasitization of fourth-instar larvae, more heavily parasitized larvae grew larger compared to those containing fewer parasitoids due to an increase in host dry weight. The differences in host mass appeared to arise after oviposition. A 'dose-dependent' enhancement of host dry weight would appear nutritionally beneficial for the parasitoids developing in more 'crowded' hosts. The efficiencies of conversion of ingested and digested food to body mass and the approximate digestibility of the diet ingested by the host caterpillar did not vary significantly with clutch size although parasitoids took slightly longer to develop in the more heavily parasitized hosts. Larval parasitoids developing in the presence of many competitors weighed up to 50% less than those developing in hosts with fewer endoparasitoids, although the weight of adult female parasitoids did not vary significantly with wasp clutch size. The maximum number of emerging wasps was 200 parasitoids, possibly representing the host's 'carrying capacity' for larvae parasitized in the fourth-instar. The ratio of emerging to non-emerging parasitoids decreased as parasitoid clutch size increased, with few or none emerging from very heavily parasitized hosts containing more than 400 parasitoids. Copyright 1997 Elsevier Science Ltd. All right reserved

Journal Article↗
PubMed1978

The effect of variations in host and parasite density on the level of parasitization of Lymnaea truncatula by Fasciola hepatica.

Groups of the snail Lymnaea truncatula, maintained at a range of spatial densities, were exposed to different densities of miracidia of Fasiola hepatica. The resulting degree of parasitization was measured 3--4 weeks after infection. The relationship between parasite densities and parasitization appeared to be curvilinear. The lower than expected parasitization at high parasite densities could be explained by the multiple infection of some snails by two or more miracidia. The level of parasitization was not related exponentially to the temperature at which infection was carried out. This was thought to be due to the inverse relationship between miracidial longevity and swimming speed, with respect to temperature. A depth of free water overlying a mud surface was an absolute requirement for miracidia to successfully infect snails.

Animals↗
PubMed2003

Infectivity and attenuation of Leishmania donovani promastigotes. II: Association of the loss of parasite infectivity with the terminal galactosylation of precursor acceptors present in virulent parasites by the developmentally regulated galactosyltransferase.

The beta1-4 galactosyltransferase enzyme of the Leishmania donovani promastigotes, was found to be developmentally regulated and expressed only in the attenuated parasites. The enzymatic product of soluble determinants of virulent promastigotes and the galactosyltransferase enzyme was found to stimulate the macrophage burst activity but inhibit in vitro intracellular parasitism. In contrast, removal of terminal galactose moieties from soluble determinants of attenuated parasites resulted in the inhibition of macrophage respiratory burst activity but did not now inhibit intracellular parasitism. We propose that the terminal galactosylation of acceptor substrates present in virulent parasites by the developmentally regulated galactosyltransferase is associated with loss of parasite virulence.

Animals↗
PubMed2007

Growth of the protozoan parasite Entamoeba histolytica in 5-azacytidine has limited effects on parasite gene expression.

BACKGROUND: In higher eukaryotes DNA methylation regulates important biological functions including silencing of gene expression and protection from adverse effects of retrotransposons. In the protozoan parasite Entamoeba histolytica, a DNA methyltransferase has been identified and treatment with 5-azacytidine (5-AzaC), a potent inhibitor of DNA methyltransferase, has been reported to attenuate parasite virulence. However, the overall extent of DNA methylation and its subsequent effects on global gene expression in this parasite are currently unknown. RESULTS: In order to identify the genome-wide effects of DNA methylation in E. histolytica, we used a short oligonucleotide microarray representing 9,435 genes (approximately 95% of all annotated amebic genes) and compared the expression profile of E. histolytica HM-1:IMSS parasites with those treated with 23 microM 5-AzaC for up to one week. Overall, 2.1% of genes tested were transcriptionally modulated under these conditions. 68 genes were upregulated and 131 genes down regulated (2-fold change; p-value < 0.05). Sodium-bisulfite treatment and sequencing of genes indicated that there were at least two subsets of genes with genomic DNA methylation in E. histolytica: (i) genes that were endogenously silenced by genomic DNA methylation and for which 5-AzaC treatment induced transcriptional de-repression, and (ii) genes that have genomic DNA methylation, but which were not endogenously silenced by the methylation. We identified among the genes down regulated by 5-AzaC treatment a cysteine proteinase (2.m00545) and lysozyme (52.m00148) both of which have known roles in amebic pathogenesis. Decreased expression of these genes in the 5-AzaC treated E. histolytica may account in part for the parasites reduced cytolytic abilities. CONCLUSION: This work represents the first genome-wide analysis of DNA-methylation in Entamoeba histolytica and indicates that DNA methylation has relatively limited effects on gene expression in this parasite.

Animals↗
PubMed1993

A host-parasite model yielding heterogeneous parasite loads.

Many models of parasitic infections lead to an approximately Poisson distribution of parasites among hosts, in stark contrast to the highly over-dispersed distributions that are usually encountered in practice. In this paper, a model is analyzed which, while assuming all individuals to be alike, can still lead to a very heterogeneous distribution of parasites among the host population. The model can be viewed as a very simple mean field interacting particle system, with the particles corresponding to the individual hosts, which behaves like an associated deterministic system when the number of hosts is large. The deterministic system describes the evolution over time of the proportions of the population with different parasite loads and its equilibria are interpreted as typical distributions of parasites among hosts. Despite its simplicity, the model is complicated enough mathematically to leave a number of open problems.

Animals↗
PubMed2000

Emerging parasite zoonoses: the role of host-parasite relationship.

Human-parasite relationships have played an essential role in the emergence or re-emergence of some parasitic diseases. These interactions are due to numerous causes. Some are linked to humans (immunodeficiencies due to AIDS among other causes, treatments, nosocomial contaminations, genetic predisposition), others concern the parasite (particular genotypes having modified their parasitic specificity). Several of these causes were predominant in the emergence of parasitoses such as cryptosporidiasis, microsporidioses or, to a certain point, pneumocystosis, the transmission of which has become zoonotic or even anthroponotic, inter-human. Re-emergent diseases (toxoplasmosis, leishmaniasis, giardiasis, strongyloidiasis, scabies) had already been described in human pathology, but their frequency or symptomatology have been drastically modified. In this case also, the unbalanced host-parasite relationship is largely responsible but it can not be dissociated from other causes, especially environmental and nutritional.

Animals↗
PubMed2004

Immune response to fleas in a wild desert rodent: effect of parasite species, parasite burden, sex of host and host parasitological experience.

We studied immune responses of the jird Meriones crassus to different flea species belonging to the same family. We used jirds maintained in an outdoor enclosure (enclosure; N=18) and parasitized by fleas Xenopsylla conformis mycerini and Xenopsylla ramesis, and also jirds born in the laboratory to previously parasitized mothers (laboratory animals; N=23). We asked (i) whether cross-immunity to different fleas occurs, (ii) whether there is a sex difference in immune responses to flea parasitism and (iii) whether the severity of the immune responses depends on parasite load. In the enclosure animals, immune response to antigen from the unfamiliar flea Synosternus cleopatrae pyramidis did not differ from those to antigens from the familiar fleas. In contrast, laboratory rodents demonstrated no difference in the immune response between S. c. pyramidis antigen and either the phytohemagglutinin treatment or controls, although their responses to antigens of fleas familiar to their mothers (X. c. mycerini and X. ramesis) were significantly higher than those to antigen of S. c. pyramidis and phytohemagglutinin. The results clearly demonstrated that (i) cross-reactivity in rodent responses to different flea species occurred for enclosure but not for laboratory jirds and (ii) immune-naïve animals whose mothers were parasitized by fleas had some degree of immunity against fleas. The only sex difference in immunological parameters was the higher level of circulating immune complexes in females than in males. Only phagocytic activity was affected by flea burden, decreasing with an increase in flea numbers.

Analysis of Variance↗