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PubMed2001

Coevolution in host-parasite systems: behavioural strategies of slave-making ants and their hosts.

Recently, avian brood parasites and their hosts have emerged as model systems for the study of host-parasite coevolution. However, empirical studies of the highly analogous social parasites, which use the workers of another eusocial species to raise their own young, have never explicitly examined the dynamics of these systems from a coevolutionary perspective. Here, we demonstrate interpopulational variation in behavioural interactions between a socially parasitic slave-maker ant and its host that is consistent with the expectations of host-parasite coevolution. Parasite pressure, as inferred by the size, abundance and raiding frequency of Protomognathus americanus colonies, was highest in a New York population of the host Leptothorax longispinosus and lowest in a West Virginia population. As host-parasite coevolutionary theory would predict, we found that the slave-makers and the hosts from New York were more effective at raiding and defending against raiders, respectively, than were conspecifics from the West Virginia population. Some of these variations in efficacy were brought about by apparently simple shifts in behaviour. These results demonstrate that defence mechanisms against social parasites can evolve, and they give the first indications of the existence of a coevolutionary arms race between a social parasite and its host.

Animals↗
PubMed2002

Intraspecific brood parasitism can increase the number of eggs that an individual lays in its own nest.

Intraspecific brood parasitism involves laying eggs in the nest of another individual of the same species without subsequently caring for the eggs or hatchlings. Where individuals lay in their own nest as well as parasitically, previous works predicted that parasitism leads to fewer eggs being laid in an individual's own nest, compared with the equivalent situation without parasitism. This is predicted to occur both to reduce the effects of competition from parasitically laid individuals and because parasitism can be used to reduce competition between siblings. Here, we present a quantitative model of this situation. This model indicates that the brood-reduction prediction does not hold universally. For some plausible parameter combinations, parasitism causes an increase rather than a decrease in the number of eggs laid by an individual in its own nest. This occurs because parasitism becomes a less profitable tactic as more eggs are laid by nest owners due to increasing within-nest competition. Increasing clutch size will also increase competition between the host's own offspring, but can still be advantageous if the induced reduction in parasitism is sufficient.

Animals↗
PubMed2001

Positive genetic correlation between parasite resistance and body size in a free-living ungulate population.

Parasite resistance and body size are subject to directional natural selection in a population of feral Soay sheep (Ovis aries) on the island of St. Kilda, Scotland. Classical evolutionary theory predicts that directional selection should erode additive genetic variation and favor the maintenance of alleles that have negative pleiotropic effects on other traits associated with fitness. Contrary to these predictions, in this study we show that there is considerable additive genetic variation for both parasite resistance, measured as fecal egg count (FEC), and body size, measured as weight and hindleg length, and that there are positive genetic correlations between parasite resistance and body size in both sexes. Body size traits had higher heritabilities than parasite resistance. This was not due to low levels of additive genetic variation for parasite resistance, but was a consequence of high levels of residual variance in FEC. Measured as coefficients of variation, levels of additive genetic variation for FEC were actually higher than for weight or hindleg length. High levels of additive genetic variation for parasite resistance may be maintained by a number of mechanisms including high mutational input, balancing selection, antagonistic pleiotropy, and host-parasite coevolution. The positive genetic correlation between parasite resistance and body size, a trait also subject to sexual selection in males, suggests that parasite resistance and growth are not traded off in Soay sheep, but rather that genetically resistant individuals also experience superior growth.

Alleles↗
PubMed2000

Cryptosporidium parvum induces host cell actin accumulation at the host-parasite interface.

Cryptosporidium parvum is an intracellular protozoan parasite that causes a severe diarrheal illness in humans and animals. Previous ultrastructural studies have shown that Cryptosporidium resides in a unique intracellular compartment in the apical region of the host cell. The mechanisms by which Cryptosporidium invades host intestinal epithelial cells and establishes this compartment are poorly understood. The parasite is separated from the host cell by a unique electron-dense structure of unknown composition. We have used indirect immunofluorescence microscopy and confocal laser scanning microscopy to characterize this structure. These studies indicate that host filamentous actin is assembled into a plaque-like structure at the host-parasite interface during parasite invasion and persists during parasite development. The actin-binding protein alpha-actinin is also present in this plaque early in parasite development but is lost as the parasite matures. Other actin-associated proteins, including vinculin, talin, and ezrin, are not present. We have found no evidence of tyrosine phosphorylation within this structure. Molecules known to link actin filaments to membrane were also examined, including alpha-catenin, beta-catenin, plakoglobin, and zyxin, but none was identified at the host-parasite junction. Thus, Cryptosporidium induces rearrangement of the host cell cytoskeleton and incorporates host cell actin and alpha-actinin into a host-parasite junctional complex.

Actins↗
PubMed2003

Transfected Plasmodium knowlesi produces bioactive host gamma interferon: a new perspective for modulating immune responses to malaria parasites.

Transgenic pathogenic microorganisms expressing host cytokines such as gamma interferon (IFN-gamma) have been shown to manipulate host-pathogen interaction, leading to immunomodulation and enhanced protection. Expression of host cytokines in malaria parasites offers the opportunity to investigate the potential of an immunomodulatory approach by generating immunopotentiated parasites. Using the primate malaria parasite Plasmodium knowlesi, we explored the conditions for expressing host cytokines in malaria parasites. P. knowlesi parasites transfected with DNA constructs for expressing rhesus monkey (Macaca mulatta) IFN-gamma under the control of the heterologous P. berghei apical membrane antigen 1 promoter, produced bioactive IFN-gamma in a developmentally regulated manner. IFN-gamma expression had no marked effect on in vitro parasite development. Bioactivity of the parasite-produced IFN-gamma was shown through inhibition of virus cytopathic effect and confirmed by using M. mulatta peripheral blood cells in vitro. These data indicate for the first time that it is feasible to generate malaria parasites expressing bioactive host immunomodulatory cytokines. Furthermore, cytokine-expressing malaria parasites offer the opportunity to analyze cytokine-mediated modulation of malaria during the blood and liver stages of the infection.

Animals↗
PubMed1998

Metabolic changes of the malaria parasite during the transition from the human to the mosquito host.

Plasmodium falciparum is an obligate human parasite that is the causative agent of the most lethal form of human malaria. Transmission of P. falciparum to a new human host requires a mosquito vector within which sexual replication occurs. P. falciparum replicates as an intracellular parasite in man and as an extracellular parasite in the mosquito, and it undergoes multiple developmental changes in both hosts. Changes in the environment and the activities of parasites in these various life-cycle stages are likely to be reflected in changes in the metabolic needs and capabilities of the parasite. Most of our knowledge of the metabolic capabilities of P. falciparum is derived from studies of the asexual erythrocytic cycle of the parasite, the portion of the parasite life cycle found in infected humans that is responsible for malarial symptoms. Efforts to control transmission and to understand the sometimes unique biology of this parasite have led to information about the metabolic capabilities of sexual and/or sporogonic stages of these parasites. This review focuses on comparing and contrasting the carbohydrate, nucleic acid, and protein synthetic capabilities of asexual erythrocytic stages and sexual stages of P. falciparum.

Animals↗
PubMed2005

DNA vaccines against tropical parasitic diseases.

Parasitic diseases caused by protozoan and helminth parasites are among the leading causes of morbidity and mortality in tropical and subtropical regions of the world. Unfortunately, at present, there is no vaccine against any human parasitic disease. Conventional vaccine methods have largely failed against parasitic infections. This is due, in part, to the complexity of the parasite life cycle, the ability of the parasite to evade the immune system, and difficulties in identifying and eliciting the desired protective immune responses. The discovery of DNA vaccines has renewed hope for vaccine development against parasites. In the last decade, DNA vaccines were successful in inducing at least partial protection against several parasitic diseases. This review discusses the latest developments in DNA vaccines against tropical parasitic diseases.

Animals↗
PubMed1990

Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease. 4--The reflection of parasite stock in the responsiveness of different vector species to chronic infection with different Trypanosoma cruzi stocks.

Previous studies (1982, 1987) have emphasized the superiority of sylvatic vector species over domestic species as xenodiagnostic agents in testing hosts with acute or chronic infections by T. cruzi "Y" stock. The present study, which is unique in that it contains data on both infectivity rates produced by the same stock in 11 different vector species and also the reaction of the same vector species to seven different parasite stocks, establishes the general validity of linking efficiency of xenodiagnosis to the biotope of its agent. For example, infectivity rates produced by "São Felipe" stock varied from 82.5% to 98.3% in sylvatic vectors but decreased to 42.5% to 71.3% in domestic species. "Colombiana"stock produced in the same sylvatic vectors infectivity rates ranging from 12.5% to 45%. These shrank to 5%-22.5% in domestic bugs. The functional role of the biotope in the vector-parasite interaction has not been elucidated. But since this phenomenon has been observed to be stable and easy to reproduce, it leads us to believe that the results obtained are valid. Data presented also provide increasing evidence that the infectivity rates exhibited by bugs from xenodiagnosis in chronic hosts, are parasite stock specific. For example, infectivity rates produced by "Berenice", "Y", "FL" and "CL" varied in R. neglectus from 26.3% to 75%; in P. megistus from 56.3% to 83.8%; in T. sordida from 28.8% to 58.8% in T. pseudomaculata from 41.3% to 66.3% and in T. rubrovaria from 48.8% to 85%. Data from xenodiagnosis in the same hosts, carrying acute infections by the same parasite stocks, gave the five sylvatic vectors a positive rating of approximately 100%, thus suggesting that the heavy loads of parasites circulating in the acute hosts obscured the characteristic interspecific differences for the parasite stock. Nonetheless these latter were revealed in the same hosts with chronic infections stimulated by very low numbers of the same parasite stocks. Certain observations here described lead us to speculate as to the possibility of further results from other parasite stocks, allowing the association of the infectivity rates produced in bugs by different parasite stocks with the isoenzymic patterns revealed by these stocks.

Animals↗
PubMed2003

Interspecific parasite exchange in a mixed colony of birds.

Studies of avian host-parasite interactions rarely include consequences of relationships among hosts for either the host or parasite species. In this study, we examine the ectoparasitic burden of adult and nestling European bee-eaters (Merops apiaster) and rock sparrows (Petronia petronia) in a mixed colony. We found that (1) each bird species had its own species of lice; (2) hematophagous mites parasitized both adults and nestlings of both bird species; (3) Carnus hemapterus, a common parasite of nestling bee-eaters, also infested rock sparrow nestlings, a species not previously described as a host for this dipteran; and (4) whereas C. hemapterus did not show high host specificity within the colony, the emergence of adult flies was synchronized with the start of hatching in bee-eater nests. We suggest that coexistence of these 2 bird species results in parasite exchange, bee-eaters obtaining mites from sparrows and sparrows becoming infested by C. hemapterus. Differences in the detrimental effects of parasite transfer for each host species may result in a process of apparent competition mediated by shared parasites. Interspecific parasite exchange is an important aspect of host-parasite relationships in mixed colonies, which requires further attention.

Animals↗
PubMed2006

Ecological fitting as a determinant of the community structure of platyhelminth parasites of anurans.

Host-parasite associations are assumed to be ecologically specialized, tightly coevolved systems driven by mutual modification in which host switching is a rare phenomenon. Ecological fitting, however, increases the probability of host switching, creating incongruences between host and parasite phylogenies, when (1) specialization on a particular host resource is a shared characteristic of distantly related parasites, and (2) the resource being tracked by the parasite is widespread among many host species. We investigated the effect of ecological fitting on structuring the platyhelminth communities of anurans from a temperate forest and grassland in the United States and tropical dry and wet forests in Mexico and Costa Rica. The six communities all exhibit similar structure in terms of the genera and families inhabiting the frogs. Parasite species richness is highly correlated with the amount of time a host spends in association with aquatic habitats, a conservative aspect of both parasite and host natural history, and determined in a proximal sense by host mobility and diet breadth. The pattern of parasite genera and families within host genera across the regions examined is consistent with the prediction that ecological fitting by phylogenetically conservative species, coupled with historical accidents of speciation and dispersal, should be evidenced as a nested-subset structure; the shared requirement for aquatic habitats of tadpoles provides a baseline assemblage to which other parasite taxa are added as a function of adult host association with aquatic habitats. We conclude that parasite communities are structured by both ecological fitting and coevolution (mutual modification), the relative influences of which are expected to vary among different communities and associations.

Animals↗
PubMed1988

Tissue parasitic diseases in Korea.

Parasitic disease is still important subject in the field of infectious diseases in Korea considering it's number and morbidity. Recently there was conspicuous reduction of parasitic disease in terms of soil-transmitted nematodiasis, but parasitism affecting organs other than intestinal tract is still a considerable problem. This survey covers the parasitic diseases cross-sectioned at a pathology laboratory of a referral hospital, trying to elucidate the significance of its relative frequency and also to describe some histopathological changes made by different parasites. Entire pathological materials of parasitic diseases, that were referred, examined and confirmed at the Department of Pathology, Seoul National University Hospital from 1968 to 1987, were used for the study. There was a total of 594 cases of tissue parasitic diseases. This number accounted for 0.33 per cent of total accessions of surgical pathology. There occurred average 30 cases of tissue parasitic disease each year at this Hospital. Protozoal diseases were constituted of 15 cases of amebiasis, 7 cases of leishmaniasis (imported) and 5 cases of Pneumocystis carinii infections. Among helminthic infections cysticercosis was the most common (425 cases), and was followed by paragonimiasis (35 cases), sparganosis (31 cases), clonorchiasis (32 cases) and ascariasis (16 cases). In addition there were 4 cases of anisakiasis, 2 cases of fascioliasis, 2 cases of echinococcosis (imported) and a case of strongyloidiasis and a case of metagonimiasis respectively. It is emphasized that imported parasitic diseases such as leishmaniasis and hydatid disease become steadily found nowadays. Schistosomiasis is another possible imported disease, but not found in this series. And certain cestodiasis particularly cysticercosis and sparganosis should be the subjects of epidemiologic re-evaluation in view of steady occurrence of their morbidity.

Adult↗
PubMed1999

Efficacy of various chemotherapeutic agents on the growth of Spironucleus vortens, an intestinal parasite of the freshwater angelfish.

Seven chemotherapeutic agents (dimetridazole, metronidazole, pyrimethamine, albendazole, fenbendazole, mebendazole and magnesium sulfate) were examined for growth inhibition on the cultivation of Spironucleus vortens. Dimetridazole and metronidazole were effective in inhibiting the parasite's growth. At concentrations of 1 microgram ml-1 or higher, both dramatically decreased numbers of parasites. At 24 h exposure, 33% of parasites were inhibited when exposed to dimetridazole or metronidazole at concentrations of 2 and 4 micrograms ml-1, respectively. Dimetridazole at 4 micrograms ml-1 or higher concentrations decreased the number of organisms to 50% or less after 48 h exposure. During the same period of time, the numbers of parasites decreased to 50% or less when exposed to metronidazole at 6 micrograms ml-1 or higher. Pyrimethamine at concentrations of 1 to 10 micrograms ml-1 was not effective in inhibiting the parasite's growth. Albendazole and fenbendazole at concentrations of 0.1 and 0.5 microgram ml-1 were similar in inhibiting the growth of the organism. Both compounds suppressed parasite growth at concentrations of 1.0 microgram ml-1 or higher after 24 h exposure. Mebendazole inhibited the parasite's growth at concentrations of 0.5 microgram ml-1 or higher. At 72 h exposure, 45 to 50% of the parasites were inhibited when exposed to mebendazole at concentrations higher than 0.5 microgram ml-1. Magnesium sulfate at concentrations of 70 mg ml-1 or higher also suppressed the growth of parasites after 24 h exposure. These results indicate that dimetridazole, metronidazole and mebendazole are the most effective chemotherapeutic agents in vitro at inhibiting the growth of S. vortens.

Albendazole↗
PubMed1996

Comparison of two methods for enumerating malaria parasites in thick blood films.

Calculation of parasite densities is important for estimating herd immunity to malaria, and for determining end points in field trials for interventions such as malaria vaccines, impregnated bed nets, and chemosuppression. Two methods of enumeration were compared: method 1, in which 100 consecutive high-power fields (HPFs) are examined, and if they all contain at least one parasite, the number per field is then counted in 10-100 of these fields according to density; and method 2, in which the actual number of parasites present in 100 consecutive fields are counted. The first method significantly underestimates parasite density in samples in which less than all high-power fields are parasite-positive. A correction of method 1 is suggested, which results in a parasite density, which is comparable with that obtained using method 2. The correction factor estimated was 2(-In(1 - p)), where p is the proportion of positive HPFs. The correction factor presented will allow accurate estimate of parasite densities per volume of blood even if only the proportion of parasite-positive high-power fields containing at least one parasite are counted.

Animals↗
PubMed2001

Gender variations in the prevalence of parasitic infections and the level of awareness in adolescents in rural Nepal.

The study was conducted in rural school adolescent children to investigate the awareness and its association in parasitic infections in boys and girls. Of the 182 children examined 119 (65.3%) were male and 63 (34.6%) were female, age ranged 12-20 years with median age 15 years. Out of 182 stool samples examined 73 (40%) were found to be positive for parasites in which two or more parasites were found in 10 stool samples. Giardia lamblia 33 (18.1%) was the predominant parasite followed by hook worm 27 (14.8%) Entamoeba histolytica 13 (7.1%), Ascaris lumbricoides 05 (2.7%), Hyminolepis nana 02 (2.2%) and Trichuris trichiuria 01 (0.5%). Thirty-one (49.2%) in 63 females and 40 (33.6%) of the 119 males were positive for parasitic infections. The prevalence of worm infection was significantly higher in female children than male (p < or = 0.05). In contrast to the high parasitic prevalence rate in females they possessed significantly higher levels of awareness about parasitic infections. Out of 119 males 99 (83.2%) and 61 (96.8%) of the 63 females (p < or = 0.05) knew that worms suck food from host body. Similarly, 62.2% of males and 96.85 of females (p < or = 0.05) knew that parasites suck blood from human body. More study should be carried out to find out the gender difference in parasitic infection and level of exposure to risk factors.

Adolescent↗
PubMed2001

Parasitic contaminants in food.

There is a wide variety of food products that may be contaminated with one or more parasites and consequently enabling transmission to human beings. The prevalence of specific parasites in food supplies varies between countries and regions. Sources of food-borne products contaminated with parasites are pigs, cattle, fish, crabs, crayfish, snails, frogs, snakes and aquatic plants. One of the major factors influencing the prevalence of parasitic infections in the population is the habit, and traditional popularity of eating raw or inadequately cooked foods. The parasites that may be acquired by eating these foods are nematodes, trematodes, cestodes and protozoa. The major genera of parasites are Trichinella, Gnathostoma, Angiostrongylus, Anisakis, Paragonimus, Clonorchis, Opisthorchis, Fasciola, Fasciolopsis, Echinostoma, Taenia, Spirometra and Toxoplasma. These food-borne parasitic infections are public health problems worldwide. The contamination of food affects many including humans, livestock industry, agriculture, and food manufacturing and processing. Unsafe foods must be condemned and destroyed. Today there is increasing travel hence there is the risk of humans' acquiring food-borne parasitic infections through eating native food often raw. Moreover, the consumption of imported livestock and foods, especially from endemic areas of food-borne parasitic zoonoses, can be the cause of infection. Awareness should be heightened wherever and whenever raw or inadequately cooked food are consumed.

Animals↗
PubMed2001

Parasitic and bacterial contamination in collards using effluent from treated domestic wastewater in Chiang Mai, Thailand.

Thailand often has inadequate water supply for agriculture during the dry season. The reuse of treated wastewater treatment plants could solve this problem. Treatment of domestic wastewater of Chiang Mai municipality by the aerated lagoon system (AL) releases more than 25,000 m3 of treated water everyday. The reuse of wastewater in agriculture is an efficient use of water, especially in tropical countries or in drought zones. The objective of this study is to demonstrate the possibility of using treated wastewater in growing edible vegetables, ie collards (kale), without pathogenic parasite and bacterial contamination. Collards (Brassica oleracea var acephala) were grown using either the treated wastewater from the aerated lagoon system (AL) or ground water (GW). Three cropping times were scheduled in February, May and July, 2000. Samples of water from AL system and GW were taken two times per month (the consecutive weeks) from February to July and examined for bacteria and parasites. Irrigation water (IW) that was normally used in agriculture was also collected, at the same time of the AL and GW collection, for bacteria and parasite investigation. A soil sample was taken before and after each crop for parasite examination. Collards were also collected at the end of the crop for parasite investigation. The results showed that GW seems to be a clean water since no pathogenic bacteria were found although small amount of Escherichia coli was noted in May. For AL and IW, similar number and types of bacteria were found. They were Aeromonas sobria, A. hydrophila, E. coli, Citrobacter freundii, Pseudomonas aeruginosa, non-pathogenic type of Vibrio cholerae. The small number of Salmonella enteritidis gr E was found in AL in April. After investigating 12 samples in 6 months of each kind of water, ie GW, Al, and IW, no parasite was found. Only unidentified free living nematodes were found in IW but those parasites are non pathogenic. A small number of unidentified free living nematodes (UFLN), a natural parasite, were found in soil after cropping. After each cropping time, similar number of hookworm was found in the plots which used either GW or AL. Collards grown by using either GW or AL showed no harmful parasite contamination. We conclude that the effluent from wastewater treatment, using aerated lagoon system, of Chiang Mai municipality could be safely used for growing collards.

Agriculture↗
PubMed2002

[Malnutrition and its association with intestinal parasitism among children from a village in the Colombian Amazonian region].

Intestinal parasites and malnutrition cause high morbidity among children in developing countries. A study to establish the associations between intestinal parasitism and undernourishment was undertaken in a village in the Colombian Amazon region. Two hundred thirty seven children each provided four stool samples for parasitic analysis. Anthropometric indices were calculated based on height and weight (HAZ), weight and age (WAZ) and height and weight (WHZ) using the international growth standards recommended by the World Health Organization. Of the 237 children, 86.1% were carrying parasites, 54% had 2 or more parasites, 30% were stunted, 10% were underweight, and 2.5% were wasting. HAZ and WAZ indices were inversely related to age and number of parasites. Socioeconomic status was positively correlated with the number of parasites and inversely related to the HAZ index (p < 0.05). In conclusion, frequencies of undernourishment and intestinal parasites among the sample population were higher than the national average for Colombia. As previous studies have indicated, age, intestinal parasitism and socio-economic level are variables significantly related to nutritional state.

Adolescent↗
PubMed2003

Malaria parasites and red blood cells: from anaemia to transmission.

Malaria parasites, Plasmodium spp., invade and exploit red blood cells during their asexual expansion within the vertebrate host. The parasite has evolved a suite of adaptive mechanisms enabling optimal exploitation of the host blood cell environment, avoiding host destruction, maintaining a parasite reservoir of infection and producing sexual transmission stages to infect mosquitoes. The highly variable nature of the host blood environment, both over the course of an infection and as a result of other parasitic infections, has selected for the evolution of considerable phenotypic plasticity in the parasite's response to its environment, particularly those phenotypes concerning transmission of the parasite to mosquitoes. With the evolution of human society, human malaria disease is becoming an increasingly urban problem. This imposes different selection pressures on the parasite. The extent to which the parasite is truly plastic over the short term rather than adaptive over the long term will determine the urban epidemiology of malaria and is essential for developing appropriate control methods. Understanding the adaptive nature of malaria parasites is thus vital for anticipating the future visage of urban human malaria.

Adaptation, Biological↗