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 577 records · Page 32Linked to original sources
PubMed2004

Effect of sodium citrate based anticoagulants on the growth activity of malaria parasites.

OBJECTIVE: To study the effect of anticoagulants based on sodium citrate on the growth activity of malaria parasites. METHODS: The parasites were treated with 3 anticoagulants (ACD, CD and SC), respectively, and the parasitemia was determined to measure the effect of the anticoagulants on the growth of the parasites. Unsynchronized Plasmodium falciparum was treated with the anticoagulants at different concentrations for 3 h at 37 degrees C. Treated erythrocytes were mixed with normal parasites or treated parasites with normal erythrocytes, which was followed by parasitemia determination of the two cultures to determine the cell target of the anticoagulants. Stage-synchronized parasites (ring, trophozoite and schizont) were treated as above to investigate the stage target. P. berghei was also treated with anticoagulants and inoculated in mice to detect the effect of anticoagulants on the animal malaria parasite by counting the parasitemia. RESULTS: All 3 anticoagulants inhibited falciparum parasite growth and ACD had the strongest potency. The treatments of the erythrocyte and the parasite with anticoagulants respectively showed that the anticoagulants targeted the parasites rather than normal erythrocytes. Stage-synchronized parasite treatment suggested anticoagulants primarily inhibited schizonts. The effect of anticoagulants on P. berghei was similar to that on P. falciparum. CONCLUSION: ACD showed the most significant inhibitive effect on the growth of malaria parasites and SC was the best anticoagulant based on sodium citrate for malarial experiments.

Animals↗
PubMed1991

The need for live parasites for long-term immunity in malaria.

All of the results of the various experiments support a role for living, proliferating parasites in the efficient induction of anti-parasitic as well as anti-disease (CM) immunity. Non-proliferating parasites or material from disrupted parasites are poor or non-antigens in this respect. Three possibilities as to why living parasites are important in immunity could be considered: 1. circulating parasites contain insufficient antigen to induce protective immunity, but sufficient antigen can be produced during proliferation; 2. only circulating parasites arrive at critical places (e.g. parts of the white pulp of the spleen) for the presentation of the important antigen or induction of appropriate signals. 3. Architectural changes are needed (i.e. formation of barrie-cell-complexes) for the immune response to be effective. The first possibility explains why exoantigens, as well as live, proliferating parasites are efficient inducers of anti-CM immunity. Since these immunizations have no effect on parasitemia, additional/other immune reaction(s) are needed for anti-parasitic immunity. The important role of the spleen in malaria and malaria immunity is well-known. The second possibility includes the idea that live, proliferating parasites circulate through the spleen continuously where unsatisfactory or infected erythrocytes are removed rather than in the liver. Injected killed parasites or material from them when present in the circulation is to a larger extent taken up by the Kupffer cells from the liver rather than the spleen. Presence and uptake of parasites in the spleen may provide the critical confrontation and/or delivery of signals necessary for the development of immunity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Analysis of human T cell clones specific for conserved peptide sequences within malaria proteins. Paucity of clones responsive to intact parasites.

T cells are thought to be of central importance in malaria immunity. Peptides copying malaria protein sequences often stimulate human CD4+ T cells and it was thought that they represented T cell epitopes present in the parasite and may thus have particular relevance to malaria vaccine development. To verify whether synthetic peptides representing highly conserved regions of parasite Ags may contribute to a malaria vaccine, we searched the data bank for conserved regions of Plasmodium falciparum malaria proteins that were not homologous to known self (human) proteins. We synthesized 24 such peptides representing 11 of the cloned and sequenced malaria asexual stage Ags, which were predicted by algorithms to represent T cell epitopes, and 6 peptides not predicted to be T cell epitopes and used these to generate T cell clones from individuals with an extensive previous history of malaria exposure. The T cell clones responded vigorously to many peptides but only a single clone, specific for a peptide within merozoite surface protein-1, 20-39, VTHESYQELVKKLEALEDAV, and not previously defined to be a T cell epitope responded to malaria parasites by proliferation and secretion of IFN-gamma. This epitope was not revealed by studying parasite-induced T cell lines and is thus subdominant. The clone was able to significantly inhibit parasite growth in vitro. The final step in the inhibition of parasite growth appears to be nonspecific because other activated clones (not specific for malaria sequences) can inhibit parasite growth. Our data suggest that few conserved peptides within malaria parasites can be processed from the intact parasite. However, such peptides that can be processed from malaria parasites may be expected to stimulate parasite-specific T cells that could inhibit parasite growth and as such may be lead candidates for a vaccine aimed at inducing cellular immunity to malaria.

Adult↗
PubMed2005

Parasites of the superorganism: are they indicators of ecosystem health?

The concept of ecosystem health is derived from analogies with human health, which subsequently leads to the implication that the ecosystem has organismal properties, a 'superorganism' in the Clementsian sense. Its application and usefulness has been the subject of a contentious debate; yet, the term 'ecosystem health' has captured the public's imagination and woven its way into the current lexicon, even incorporated into public policy. However, the application of parasites as bioindicators of ecosystem health poses a curious conundrum. Perceptions of parasites range from mild distaste to sheer disgust among the general public, the media, environmental managers and non-parasitologists in the scientific community. Nevertheless, the biological nature of parasitism incorporates natural characteristics that are informative and useful for environmental management. The helminths in particular have evolved elegant means to ensure their transmission, often relying on complex life cycle interactions that include a variety of invertebrate and vertebrate hosts. The assemblage of these diverse parasites within a host organism potentially reflect that host's trophic position within the food web as well as the presence in the ecosystem of any other organisms that participate in the various parasite life cycles. Perturbations in ecosystem structure and function that affect food web topology will also impact upon parasite transmission, thus affecting parasite species abundance and composition. As such, parasite populations and communities are useful indicators of environmental stress, food web structure and biodiversity. In addition, there may be useful other means to utilise parasitic organisms based on their biology and life histories such as suites or guilds that may be effective bioindicators of particular forms of environmental degradation. The challenge for parasitology is to convince resource managers and fellow scientists that parasites are a natural part of all ecosystems, each species being a potentially useful information unit, and that healthy ecosystems have healthy parasites.

Animals↗
PubMed2002

Food webs and the transmission of parasites to marine fish.

Helminth parasites of fish in marine systems are often considered to be generalists, lacking host specificity for both intermediate and definitive hosts. In addition, many parasites in marine waters possess life cycles consisting of long-lived larval stages residing in intermediate and paratenic hosts. These properties are believed to be adaptations to the long food chains and the low densities of organisms distributed over broad spatial scales that are characteristic of open marine systems. Moreover, such properties are predicted to lead to the homogenization of parasite communities among fish species. Yet, these communities can be relatively distinct among marine fishes. For benthos, the heterogeneous horizontal distribution of invertebrates and fish with respect to sediment quality and water depth contributes to the formation of distinct parasite communities. Similarly, for the pelagic realm, vertical partitioning of animals with depth will lead to the segregation of parasites among fish hosts. Within each habitat, resource partitioning in terms of dietary preferences of fish further contributes to the establishment of distinct parasite assemblages. Parasite distributions are predicted to be superimposed on distributional patterns of free-living animals that participate as hosts in parasite life cycles. The purpose of this review is first, to summarize distribution patterns of invertebrates and fish in the marine environment and relate these patterns to helminth transmission. Second, patterns of transmission in marine systems are interpreted in the context of food web structure. Consideration of the structure and dynamics of food webs permits predictions about the distribution and abundance of parasites. Lastly, parasites that influence food web structure by regulating the abundance of dominant host species are briefly considered in addition to the effects of pollution and exploitation on food webs and parasite transmission.

Animals↗
PubMed2000

Richness patterns in the parasite communities of exotic poeciliid fishes.

Three species of poeciliids (Gambusia holbrooki, Xiphophorus helleri and X. maculatus) and 15 species of ecologically similar native freshwater fishes (mainly eleotrids, ambassids, melanotaeniids and retropinnids) were examined for parasite richness to investigate parasite flux, qualitative differences, quantitative differences and the structuring factors in parasite communities in the 2 fish types in Queensland, Australia. Theory suggests that poeciliids would harbour depauperate parasite communities. Results supported this hypothesis; poeciliids harboured more species-poor parasite infracommunities and regional faunas than natives (P < 0.0001), despite greater sampling effort for the former. Cluster analysis of presence/absence data for poeciliids and the 6 most-sampled native fishes revealed that parasite communities of the 2 fish groups are qualitatively distinct; the proportion of parasite species with complex life-cycles was lower in poeciliids than in native species, and Myxosporea, Microspora, Coccidia and parasitic Crustacea were all absent from poeciliids. Limited exchange of parasite species has occurred between natives and poeciliids. Logistic ordinal regression analysis revealed that fish origin (exotic or native), environmental disturbance and host sex were all significant determinants of parasite community richness (P < 0.05). Theoretical modelling suggests that poeciliids are at a competitive advantage over native fishes because of their lack of parasites.

Animals↗
PubMed1985

Nutritional aspects of parasitic infection.

The nutritional basis of the ecological relationship between parasites and their hosts is reviewed using examples of the parasitic infections of man whenever possible. Two important points are discussed first: the distinction between parasitic infection and parasitic disease, and the concepts of synergism or antagonism between undernutrition and parasitic disease. The effects of parasites on the nutritional status of the host are examined in four ways. First, in terms of the ways in which parasites can disturb nutritive processes by effects on physical activity to obtain food, and by effects on food consumption, digestion and absorption. Secondly, in terms of the nutritional cost of an infection to a parasitised host. Thirdly, in terms of the feeding, nutrition and metabolism of parasites. Finally, in terms of damage to the tissues of the host caused by parasites. Two other sections deal briefly with the transmission of parasites in food and the effects of food on parasites.

Animals↗
PubMed1996

Comparative analysis of the metazoan parasite communities of leatherjackets, Oligoplites palometa, O. saurus, and O. saliens (Osteichthyes:Carangidae) from Sepetiba Bay, Rio de Janeiro, Brazil.

One hundred and fifty-seven specimens of leatherjackets, 84 specimens of Oligoplites palometa (Cuvier), 37 specimens of O. saurus (Bloch & Schneider), and 36 specimens of O. saliens (Bloch) captured at the Sepetiba Bay, State of Rio de Janeiro, between March of 1991 and November of 1992, were necropsied to study their communities of metazoan parasites. All fishes studied were parasitized by one or more metazoan species. Eighteen parasite species were found in O. palometa and 13 parasite species were found in O. saurus and O. saliens, respectively. The digeneans were the majority of the parasite specimens collected, with 90.3%, 82.2%, and 87.7% in O. palometa, O. saurus, and O. saliens, respectively. The Simpson index was lower than 0.25 for the 3 host species, showing an absence of concentration for dominance. The similarity coefficients among the parasite communities of the 3 fish species was above 66%. The parasites of the 3 host species showed typical overdispersed pattern of distribution. Four cases of positive correlation between host's total length and prevalence and parasite intensity were found. The majority of the species did not show influence of host sex. The 3 host species had similar parasite diversity, which was not correlated with the host's total body length and there was no significant difference between male and female hosts. Oligoplites palometa and O. saurus each had one pair of ectoparasite species sharing a positive association and with a positive correlation between their intensities. No pairs of associated species were found in O. saliens. Parasites were found along the entire extension of the gastrointestinal tract of the 3 host species. The parasite communities of O. palometa, O. saurus, and O. saliens are defined as isolationists because there are few evidences of interspecific association or covariation. The presence of larval stages of cestodes and nematodes suggests that the three species of Oligoplites are at an intermediate level in the marine trophic web.

Animals↗
PubMed2003

Interactions between parasitized and unparasitized conspecifics: parasitoids modulate competitive dynamics.

Parasitism influences many aspects of a host's behavior and physiology. Therefore, parasitism is also likely to influence the competitive ability of the host. Field populations of phytophagous insects are often a mix of parasitized and unparasitized conspecifics and the inclusion of parasitism in their competitive dynamics may alter expected outcomes. We investigated the influence of parasitism by the hymenopteran parasitoid Phanerotoma franklini Gahan on the competitive interactions among larvae of its host Acrobasis vaccinii Riley. We found that parasitized larvae were poorer competitors and required less food to complete development compared to unparasitized larvae. To examine the influence of parasitism on the competitive dynamics of this system, we constructed an individual-based model parameterized with our laboratory data. The model examined the role of resource availability and parasitism rate on larval survival. The model suggests that parasitized larvae (and, hence parasitoids) experience higher levels of mortality from competition than unparasitized larvae. Further, the model also suggests that the decreased consumption of resources by parasitized larvae results in a decline in the occurrence of competition as the parasitism rate increases. We suggest that these observations may be general to many parasitoid-host systems.

Animals↗
PubMed2005

Brood parasitism by brown-headed cowbirds and the expression of sexual characters in their hosts.

Interspecific brood parasites may use the secondary sexual characters of the hosts to decide which species to parasitize. Hence, species with conspicuous and well-recognisable traits may have higher chances of becoming parasitised. Using North American birds and their frequent brood parasite, the brown-headed cowbird Molothrus ater, we tested the relationship between features of song and plumage coloration of hosts and the frequency of brood parasitism while controlling for several potentially confounding factors. Relying on two sets of analysis, we focused separately on the evolutionary view of the parasite and the host. From the cowbird's perspective, we found that males of heavily parasitized species posit songs with low syllable repertoire size, shorter inter-song interval and have brighter plumage. From the host's perspective, a phylogenetic analysis revealed similar associations for features of song, but not for plumage characteristics that were unrelated to brood parasitism. These comparative findings may imply that brood parasites choose novel hosts based on heterospecific signals; and/or host species working against sexual selection escape from brood parasitism by evolving inconspicuous sexual signals. Although our data do not allow us to distinguish between these two evolutionary scenarios, our results suggest that selection factors mediating cowbird parasitism via host recognition by heterospecific signals may have an important role in the evolutionary relationship between brood parasites and their hosts.

Animals↗
PubMed2004

Antigenic glycans in parasitic infections: implications for vaccines and diagnostics.

Infections by parasitic protozoans and helminths are a major world-wide health concern, but no vaccines exist to the major human parasitic diseases, such as malaria, African trypanosomiasis, amebiasis, leishmaniasis, schistosomiasis, and lymphatic filariasis. Recent studies on a number of parasites indicate that immune responses to parasites in infected animals and humans are directed to glycan determinants within cell surface and secreted glycoconjugates and that glycoconjugates are important in host-parasite interactions. Because of the tremendous success achieved recently in generating carbohydrate-protein conjugate vaccines toward microbial infections, such as Haemophilus influenzae type b, there is renewed interest in defining parasite-derived glycans in the prospect of developing conjugate vaccines and new diagnostics for parasitic infections. Parasite-derived glycans are compelling vaccine targets because they have structural features that distinguish them from mammalian glycans. There have been exciting new developments in techniques for glycan analysis and the methods for synthesizing oligosaccharides by chemical or combined chemo-enzymatic approaches that now make it feasible to generate parasite glycans to test as vaccine candidates. Here, we highlight recent progress made in elucidating the immunogenicity of glycans from some of the major human and animal parasites, the potential for developing conjugate vaccines for parasitic infections, and the possible utilization of these novel glycans in diagnostics.

Animals↗
PubMed2005

Patterns of host specificity and transmission among parasites of wild primates.

Multihost parasites have been implicated in the emergence of new diseases in humans and wildlife, yet little is known about factors that influence the host range of parasites in natural populations. We used a comprehensive data set of 415 micro- and macroparasites reported from 119 wild primate hosts to investigate broad patterns of host specificity. The majority (68%) of primate parasites were reported to infect multiple host species, including animals from multiple families or orders. This pattern corresponds to previous studies of parasites found in humans and domesticated animals. Within three parasite groups (viruses, protozoans and helminths), we examined parasite taxonomy and transmission strategy in relation to measures of host specificity. Relative to other parasite groups, helminths were associated with the greatest levels of host specificity, whereas most viruses were reported to infect hosts from multiple families or orders. Highly significant associations between the degree of host specificity and transmission strategy arose within each parasite group, but not always in the same direction, suggesting that unique constraints influence the host range of parasites within each taxonomic group. Finally characteristics of over 100 parasite species shared between wild primates and humans, including those recognised as emerging in humans, revealed that most of these shared parasites were reported from multiple host orders. Furthermore, nearly all viruses that were reported to infect both humans and non-human primates were classified as emerging in humans.

Animals↗
PubMed1999

The optimal strategy for brood-parasitism: how many eggs should be laid in the host's nest?

We consider the optimal strategy for intra-specific brood-parasitism, especially with respect to the number of eggs laid by the parasitic individual in the nest of non-parasitic individual, in particular, a host that does not reject the parasite's eggs. With a fundamental mathematical model, assuming that the survival probability of the parasite's offspring in the nest of the host is significantly smaller than that in parasite's own nest, we determine the optimal number of eggs laid in the nest of host that maximizes the expected reproductive fitness of the parasite. We show that the invasion success of brood-parasitism could significantly depend on the total number of eggs laid by the parasite in a breeding season, and that the successfully invading brood-parasitism could realize maximum fitness with a specific number of parasite's eggs laid in the nest of the host.

Animals↗
PubMed2003

Habitat overlap and gastrointestinal parasitism in sympatric African bovids.

Gastrointestinal parasite infections are widespread among wild ungulates. Because many of these parasites infect multiple host species, inter-specific interactions among hosts potentially play an important role in parasite transmission dynamics in ungulate communities. In this study, the effects of inter-specific contact on parasitism rates in 11 sympatric African bovids was examined using habitat overlap among species as a measure of cross-species contact rates. Across individual hosts, strongyle nematode abundance increased with increasing numbers of bovid species occupying a habitat. Furthermore, comparative analyses show a positive association between strongyle prevalence and level of habitat overlap across taxa. These findings suggest that among sympatric bovids, contact between species contributes significantly to the transmission of generalist nematode parasites. For a more host-specific parasite group, coccidia, parasite abundance and individual probability of infection declined in hosts living in bovid rich habitats. This pattern may reflect enhanced interspecific competition among parasites in these areas. Finally, similar to strongyle abundance, individual parasite richness also increased among hosts occupying habitats with higher numbers of bovid species. No association between habitat overlap and parasite richness was detected at higher taxonomic scales, however, which suggests that contact between host species may not contribute to parasite colonization of new host taxa.

Animals↗
PubMed2005

Ecological impacts of the microsporidian parasite Pleistophora mulleri on its freshwater amphipod host Gammarus duebeni celticus.

The microsporidian parasite, Pleistophora mulleri, infects the abdominal muscle of the freshwater amphipod Gammarus duebeni celticus. We recently showed that P. mulleri infection was associated with G. d. celticus hosts being more vulnerable to predation by the invasive amphipod Gammarus pulex. Parasitized G. d. celticus also had a reduced ability to prey upon other co-occurring amphipods. We suggested the parasite may have pervasive influences on host ecology and behaviour. Here, we examine the association between P. mulleri parasitism and parameters influencing individual host fitness, behaviour and interspecific interactions. We also investigate the relationship between parasite prevalence and host population structure in the field. In our G. d. celticus study population, P. mulleri prevalence was strongly seasonal, ranging from 8.5% in summer to 44.9% in winter. The relative abundance of hosts with the heaviest parasite burden increased during summer, which coincided with high host mortality, suggesting that parasitism may regulate host abundance to some degree. Females were more likely to be parasitized than males and parasitized males were paired with smaller females than unparasitized males. Parasitism was associated with reduction in the host's activity level and reduced both its predation on the isopod Asellus aquaticus and aggression towards precopula pairs of the invasive G. pulex. We discuss the pervasive influence of this parasite on the ecology of its host.

Amphipoda↗
PubMed1990

Effects of host age, host density and parent age on reproduction of the filth fly parasite Urolepis rufipes (Hymenoptera: Pteromalidae).

Urolepis rufipes Ashmead, a pteromalid wasp, was recently discovered parasitizing house fly and stable fly pupae in eastern Nebraska dairies. Studies have been conducted on the biology of this parasite to evaluate its potential as a biological control agent of stable flies (Stomoxys calcitrans (L.] and house flies (Musca domestica L.). House fly pupae were suitable as hosts for U.rufipes at all ages; however, significantly higher parasitism occurred on host pupae aged 96-120 h. Parasite-induced mortality (host mortality without progeny production) was higher than for other pteromalid parasites of filth flies under similar conditions. Parasitism increased with parasite--host ratio at 20 degrees C; however, the opposite was noted at 30 degrees C for parasite--host ratios ranging from 5:50 to 50:50. Fly eclosion decreased as parasite--host ratio increased at 20 degrees C, and no host eclosion occurred at the highest parasite--host ratios (20:50 and 50:50) at 30 degrees C. Females produced an average of 18.6 female and 7.6 male progeny. 88% of the progeny were produced during the first 6 days post parental eclosion. The short life span, low progeny emergence rate and high per cent host eclosion, in comparison with other parasite species, suggests that the Nebraska strain of U.rufipes may not an effective biological control agent of house flies.

Age Factors↗
PubMed2002

Modulating the modulators: parasites, neuromodulators and host behavioral change.

Neuromodulators can resculpt neural circuits, giving an animal the behavioral flexibility it needs to survive in a complex changing world. This ability, however, provides parasites with a potential mechanism for manipulating host behavior. This paper reviews three invertebrate host-parasite systems to examine whether parasites can change host behavior by secreting neuromodulators. The parasitic wasp, Cotesia congregata, suppresses host feeding partly by inducing the host (Manduca sexta) to increase the octopamine concentration in its hemolymph. The increased octopamine concentration disrupts the motor pattern produced by the frontal ganglion, preventing the ingestion of food. Polymorphus paradoxus (Acanthocephalan) alters the escape behavior of its host, Gammarus lacustris (Crustacea), possibly through an effect on the host's serotonergic system. The trematode Trichobilharzia ocellata inhibits egg-laying in its snail host (Lymnaea stagnalis), partly by inducing the host to secrete schistosomin. Schistosomin decreases electrical excitability of the caudodorsal cells. The parasite also alters gene expression for some neuromodulators within the host's central nervous system. In at least two of these three examples, it appears that the host, not the parasite, produces the neuromodulators that alter host behavior. Producing physiologically potent concentrations of neuromodulators may be energetically expensive for many parasites. Parasites may exploit indirect less energetically expensive methods of altering host behavior. For example, parasites may induce the host's immune system to produce the appropriate neuromodulators. In many parasites, the ability to manipulate host behavior may have evolved from adaptations designed to circumvent the host's immune system. Immune-neural-behavioral connections may be pre-adapted for parasitic manipulation.

Animals↗
PubMed2004

Intestinal parasites prevalence and related factors in school children, a western city sample--Turkey.

BACKGROUND: Intestinal parasitic infections are amongst the most common infections worldwide. Epidemiological research carried out in different countries has shown that the social and economical situation of the individuals is an important cause in the prevalence of intestinal parasites. Previous studies in Turkey revealed a high prevalence of intestinal parasitic infection. The objectives of the current study were to determine the prevalence of intestinal parasitic infections in Aydin among 7-14 years old school children and to identify associated socio-demographic and environmental factors, behavioral habits and also related complaints. METHODS: Multistage sampling was used in the selection of the study sample. A questionnaire, cellulose adhesive and a stool specimen examination were done. RESULTS: A total of 456 stool specimens were collected. 145 students (31.8%) were infected with one or more intestinal parasites. 29 (6.4%) of the students were infected more than one parasite, 26 (5.7%) with two parasites and 3 (0.7%) with three parasites. The three most common were E. vermicularis, G. intestinalis and E. coli. Intestinal parasite prevalence was higher in rural area, in children with less than primary school educated mother, in children who use hands for washing anal area after defecation, and in children who use toilet paper sometimes or never. The relation between child health and mother education is well known. Children were traditionally taught to wash anal area by hand. Toiler paper usage was not common and might be due to low income or just a behavioral habit also. Most of the complaints of the study population were not significantly related with the intestinal parasitic infection. CONCLUSIONS: Intestinal parasitic infection is an important public health problem in Aydin, Turkey. Rural residence, mother education less than primary school, sometimes or never usage of toilet paper, and washing anal area by hands after defecation were the significant associations. Interventions including health education on personal hygiene to the students and to the parents, especially to mothers are required. The ratio of uneducated women should be declined with specific programs. A multisectoral approach is needed.

Adolescent↗