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[The environment of the Moscow megalopolis and the problems of parasitic contamination].

Studying parasitic contamination is regarded as an individual research trend for large-scale land and water areas whose natural habitat is greatly modified by man-made influences. On the one hand, parasitic contamination as its particular form acts as a factor that destabilizing the environment, on the other, the man-made deformation of natural biocenoses, which is induced by socioeconomic influences promote its occurrence and manifestations. The investigations of parasitic contamination are beyond the scope of the routine parasitological goals, though they involve their whole package and should be considered as an ecological objective of environmental protection. The cenotic communications of the links of the parasitic systems with the physicochemical and biological ingredients of the habitat predetermine qualitative and quantitative differences of parasitic contamination in the large urban areas and, finally, the dissimilar course of epidemiological, epizootic, and phytototic processes in parasitic diseases in their various sectors. The major factors influencing the levels of the parasitic pollution of the Moscow megalopolis were analyzed. These included various lines of economic activities, the population's living conditions, procedures for manufacturing foodstuffs, demographic changes. In the recent years, the situation in many parasitic infections in man (trichinosis, cryptobiasis, enterobiasis, toxocariasis, etc.), animals (fascioliasis, trichinosis, etc.) and plants (viral, fungal, and nematode diseases). There is an increase in the population of mosquitos, lice, fleas, and other insects which are vectors of dangerous parasitic diseases of man and animals.

Animals↗
PubMed2000

Nest desertion and cowbird parasitism: evidence for evolved responses and evolutionary lag.

Nest desertion with subsequent renesting is a frequently cited response to parasitism by the brown-headed cowbird, Molothrus ater, yet the role of desertion as an antiparasite defence is widely debated. To determine whether desertion represents an evolutionary response to brown-headed cowbird parasitism, we searched the primary literature, yielding data on the desertion frequencies of 60 host populations from 35 species. Species were categorized according to three habitat types (forest, intermediate and nonforest). Because cowbirds prefer open habitat and rarely penetrate deeply into forests, nonforest species have long been exposed to widespread cowbird parasitism, whereas forest species have not. However, due to increased forest fragmentation, forest species are being increasingly exposed to extensive parasitism. The frequency of desertion of parasitized nests was significantly higher in nonforest than forest species, suggesting that the latter experience evolutionary lag. We also considered whether desertion is affected by predation frequency, degree of current or recent sympatry with cowbirds, parasitism frequency, length of host laying season, phylogenetic relationships, and potential cost of cowbird parasitism. None of these variables created biases that could account for the observed difference in desertion frequencies of nonforest and forest species. However, species that incur large costs when parasitized had higher desertion rates among nonforest species but not among forest species. These results indicate that increased nest desertion is an evolved response to cowbird parasitism, as one would otherwise expect no relationship between desertion frequency and thezx costs and length of exposure to cowbird parasitism. Although nearly all hosts have eggs easily distinguished from cowbird eggs, few or none desert in response to cowbird eggs. Instead, desertion may be a response to adult cowbirds. The scarcity of species that desert in response to cowbird eggs suggests that egg recognition is more difficult to evolve than heightened desertion tendencies and that egg recognition quickly leads to ejection behaviour once it does develop. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2001

Relic behaviours, coevolution and the retention versus loss of host defences after episodes of avian brood parasitism.

Most previous studies of brood parasitism have stressed that host defences, such as egg recognition, are lost in the absence of parasitism. Such losses could result in coevolutionary cycles in which parasites shift away from well-defended hosts only to switch back to them later at a time when these hosts have lost much or all of their defences and the parasite's current hosts have built up effective defences. However, the alternative 'single trajectory' model predicts that parasites rarely switch back to old hosts because ex-hosts retain egg recognition for long periods in the absence of parasitism. If true, egg recognition by the host may be a 'relic behaviour', because in the absence of parasitism its adaptive value is close to neutral. Using artificial nonmimetic eggs, I tested for egg recognition in two populations that are currently unparasitized but that are descended from lineages likely to have been parasitized in the past: the grey catbird, Dumetella carolinensis, on Bermuda and the loggerhead shrike, Lanius ludovicianus, in California. Both of these populations showed long-term retention, ejecting nonmimetic eggs at rates of nearly 100%. Because potential present-day selection pressures, such as conspecific parasitism, do not explain this egg recognition, Bermuda catbirds apparently retain recognition from North American conspecifics that were cowbird hosts before colonizing Bermuda and shrikes retain recognition from Old World congeners that were hosts of cuckoos. Retention is also indicated by passerines in California and the Caribbean that had high rejection rates of nonmimetic eggs before coming into contact with cowbirds. These new data suggest that both the coevolutionary cycles and single trajectory models have importance and that rejection behaviour can have insignificant costs, which is consistent with evolutionary lag explanations for the acceptance of parasitic eggs shown by some cuckoo and many cowbird hosts. Copyright 2001 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2006

Parasite diversity of sticklebacks from the Baltic Sea.

In the brackish Baltic Sea, the species richness and diversity of parasite communities of three- (Gasterosteus aculeatus) and nine-spined sticklebacks (Pungitius pungitius) were investigated. The studies regarded four localities at the Schleswig-Holstein and Mecklenburg coasts, northern Germany, where salinities were between 10 and 18 per thousand. Species richness was relatively high, attaining 15 parasite species in G. aculeatus and 16 in P. pungitius, which are only surpassed by former investigations that lasted a year or more. An analysis of parasite species identity revealed clear differences in diverse localities referring to different supracommunities. The infracommunity comprised maximally of eight species in G. aculeatus and seven in P. pungitius, which corresponds to former investigations. The mean value of infracommunity with 5.3 parasites is the highest value ever found in small-sized fish. An infracommunity index revealed that the digenean Podocotyle atomon and Magnibursatus caudofilamentosa and the copepod Thersitina gasterostei were the most abundant parasites. The relationship of component community to mean infracommunity can judge about the threshold level, which allows parasite to settle successfully. An important factor to form parasite communities is the season of their appearance, which depends also on their reproduction and on the presence of intermediate hosts. In addition, the choice of prey (for passive infection) and quality of habitats (for active infection) influences the constitution of the parasite communities. The diversity values of parasites were low in all hosts, which is due to the brackish milieu and by different levels of eutrophication, which both create extreme environments. These do not mirror in every case the biodiversity of the respective habitats. The parasite community was in a level of early heterotrophic succession where low diversity is combined with high population density, which is characteristic for extreme environments. Therefore, intraspecific competition dominates and niches are wide. Under this aspect and regard of the actually valid definition that niches are dynamic systems between organisms and environment, the theory of vacant niches of some authors can be rejected.

Animals↗
PubMed1993

Quantification of parasite aggregation: a simulation study.

A simulation study is used to examine the statistical behaviour of estimators of parameters of parasite infection in relation to variation in sample size, the degree of parasite aggregation, and mean parasite burden. The most important patterns to emerge are the associations between estimates of parameters and sample size (= number of host individuals). As sample size decreases values of sample mean parasite burden, its associated variance, and the level of parasite aggregation are all systematically underestimated. The geometric mean of parasite burden and the prevalence of infection appear to be independent of associations with other parasite parameters. Estimates of parameter values may also depend on the underlying frequency distribution, but appear insensitive to variation in the population mean parasite burden. Results are discussed in relation to the interpretation of data derived from field-based studies. In particular, establishing the form of the relationship between host age and mean parasite burden and/or the degree of parasite aggregation. It is typical for sample size to decline as a function of host age within cross-sectional field data. This may give rise to artefactual patterns in the shape of age-aggregation curves in which sample sizes are unequal among host age classes.

Animals↗
PubMed1993

Identification of Plasmodium vivax-like human malaria parasite.

There are four species of human malarial parasite and several monkey ones, and in evolutionary terms the human and non-human primate plasmodia may be related. The tools of molecular biology have lately pointed to the existence of two types of Plasmodium vivax. Using specific oligonucleotides we have identified a human malaria parasite resembling P vivax under the microscope but with circumsporozoite (CS) protein differing from those of P vivax types 1 and 2. The CS protein of this "P vivax-like" malaria parasite is identical to that of P simiovale, a monkey parasite resembling P ovale, a human one, morphologically. Polyclonal serum raised against a partial repeat sequence of the P vivax-like malaria parasite specifically reacted with P simiovale sporozoites but not with those of P vivax types 1 and 2, P ovale, or P simium. Sera collected from people living in malaria endemic regions of Papua New Guinea and Brazil contained antibodies that specifically reacted with the synthetic peptides representing the repeat sequences of CS protein of this P vivax-like parasite. A comparison of the CS protein gene sequences of P simiovale and the P vivax-like malaria parasites with those of other primate parasites, data on serological cross-reactivity, and 18S ribosomal DNA analyses suggest that the new human malaria parasite described here is distinct from P falciparum, P malariae, P vivax, and P ovale, the four known species of human parasite.

Animals↗
PubMed1984

Oxygen consumption in mosquito larvae parasitized by Romanomermis culicivorax (Nematoda).

The effect of parasitism by Romanomermis culicivorax on the oxygen consumption of three species of mosquito larvae was studied by manometric methods. The Q02 of Culex pipiens, both parasitized and unparasitized, decreased as the host larvae developed from the second to fourth instar. In the early stages there was no significant difference in Q02 in parasitized and unparasitized hosts but the Q02 increased significantly in parasitized fourth instar larvae. The Q02 of parasitized and unparasitized fourth instars of Aedes taeniorhynchus, Anopheles quadrimaculatus and C. pipiens were compared. The Q02 of all parasitized hosts was significantly increased and the Q02 of the two culicine species displayed a dramatic increase in oxygen consumption. The oxygen consumption of the parasitic mermithid larvae was estimated from that obtained earlier for the post-parasitic larvae but did not account for more than 9-36% of the increased Q02 of the parasitized hosts. On this basis it seems probable that the increased metabolic rate as reflected by oxygen consumption of the parasitized mosquito larve was principally a manifestation of the physiological and nutritional stress induced by the mermithid nematodes.

Animals↗
PubMed2006

Drug transport mechanisms in helminth parasites: passive diffusion of benzimidazole anthelmintics.

Anthelmintic molecules must reach their receptors inside target parasites to exert the pharmacological effect. Available data suggest that the main route of entry of antiparasitic drugs into helminth parasites would be through their external surface. However, it is unclear if trans-tegumental/cuticular penetration is the most important way of entry of benzimidazole (BZD) anthelmintics into their target parasites compared to oral ingestion. The relative involvement of active and passive transport mechanisms has not been defined. The goal of the work reported here was to determine the main processes involved in the entry of BZD anthelmintic molecules into the three main classes of helminth parasites. Adult specimens of Moniezia benedeni (cestode), Fasciola hepatica (trematode) and Ascaris suum (nematode) were incubated in Kreb's Ringer Tris buffer (pH 7.4, 37 degrees C) (1g parasite/10 ml incubation medium) for 15, 45, and 90 min, respectively, in the presence of a concentration gradient of either fenbendazole (FBZ), oxfendazole or triclabendazole sulphoxide (TCBZSO) (1-30 mol/ml, n=4). Dead helminth specimens were also incubated with the same drug concentration gradient. Specimens of F. hepatica with the oral route closed off by ligation were incubated with TCBZSO in the presence or absence of bovine serum albumin. After the incubation time elapsed, samples of parasite material were chemically extracted and prepared for high performance liquid chromatography analysis to measure drug/metabolite concentrations. Equivalent drug concentrations were measured within ligated and non-ligated liver flukes, demonstrating that BZD do mainly penetrate by trans-tegumental diffusion. The higher the concentration of BZD molecules in the incubation medium, the greater their concentration recovered within the helminth parasites. High correlation coefficients (>0.98) were obtained between initial drug concentration in the incubation medium and those measured inside the nematode, cestode, and trematode parasites. FBZ concentrations recovered from tissues of dead cestodes/nematodes over time were significantly greater compared to those measured in living parasites. These differences in drug diffusion may be related to the morphological/functional properties of the parasite's external surfaces. The outcome of the work reported here indicates that passive drug transfer through the external helminth surface is the main transport mechanism accounting for BZD accumulation into target parasites.

Animals↗
PubMed2006

Variation in infection parameters among populations within parasite species: intrinsic properties versus local factors.

Within any parasite species, variation among populations in standard infection parameters (prevalence, intensity and abundance) is an accepted fact. The proportion of hosts infected and the mean number of parasites per host are not fixed values across the entire geographic range of any parasite species. The question is whether this inter-population variation occurs within a narrow, species-specific range and is thus driven mainly by the biological features of the parasite, or whether it is substantial and unpredictable, leaving population parameters at the mercy of local conditions. Here, the repeatability of estimates of prevalence, intensity and abundance of infection was assessed across populations of the same parasite species, for 77 metazoan parasite species of Canadian freshwater fishes. Overall, parameter values from different populations of the same parasite species were more similar to each other and more different from those of other species, than expected by chance alone. Much of the variation in parameter values in the dataset was associated with differences between parasite species, rather than with differences among populations within species. This was particularly true for intensity and abundance of infection; in contrast, prevalence values, while somewhat repeatable among populations of the same species, still showed considerable variation. Among the higher taxa investigated (monogeneans, trematodes, cestodes, nematodes, acanthocephalans, copepods), there was no evidence that species of one taxon display intrinsically greater variation in population parameters than species of other taxa. Overall, the results suggest that intensity and abundance of infection are real species characters, though somewhat variable. This conclusion supports the view that the biological features of parasite species can potentially override local environmental conditions in driving parasite population dynamics.

Animals↗
PubMed2006

Isotype patterns of immunoglobulins: hallmarks for clinical status and tissue parasite density in Brazilian dogs naturally infected by Leishmania (Leishmania) chagasi.

The role of anti-leishmanial immune response underlying the susceptibility/resistance during canine visceral leishmaniasis (CVL) has been recognized throughout ex vivo and in vitro investigations. Recently, we demonstrated that immunoglobulin levels (Igs), as well as the parasite load are relevant hallmarks of distinct clinical status of CVL. To further characterize and upgrade the background on this issue, herein, we have evaluated, in Leishmania (Leishmania) chagasi naturally infected dogs, the relationship between tissue parasitism (skin, bone marrow, spleen, liver and lymph node), the CVL clinical status (asymptomatic (AD), with no suggestive signs of the disease; oligosymptomatic (OD), with maximum three clinical signs-opaque bristles; localized alopecia and moderate loss of weight; symptomatic (SD), serologically positive with severe clinical signs of visceral leishmaniasis), and the humoral immunological profile of anti-Leishmania immunoglobulins (IgG, IgG1, IgG2, IgM, IgA and IgE). Our major statistically significant findings revealed distinct patterns of tissue parasite density within L. chagasi-infected dogs despite their clinical status, pointing out the spleen and skin as the most relevant sites of high parasitism during ongoing CVL. Parasite density of bone marrow and spleen were the most reliable parasitological markers to decode the clinical status of CVL. Moreover, the parasite density of bone marrow better correlates with most anti-Leishmania Igs reactivity. Additionally, a prognostic hallmark for canine visceral leishmaniasis was found, highlighting strong correlation between IgG1 and asymptomatic disease, but with IgA, IgE and IgG2 displaying better association with symptomatic disease. The new aspects of this study highlighted pioneer findings that correlated the degree of tissue parasite density (low (LP), medium (MP) and high (HP) parasitism) with distinct patterns of anti-Leishmania Igs reactivity. In this scope, our data re-enforce the anti-Leishmania IgG but with IgA reactivity as the better marker for overall tissue parasitism. The association between clinical status, Ig profile and the tissue parasitism support a novel investigation on the impact of humoral immune response and susceptibility/resistance mechanism during ongoing CVL.

Animals↗
PubMed2002

Metabolic and symbiotic interactions in amino acid pools of the pea aphid, Acyrthosiphon pisum, parasitized by the braconid Aphidius ervi.

Aphidius ervi Haliday (Hymenoptera, Braconidae) is an endophagous parasitoid of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera, Aphididae). This parasitoid strongly redirects host reproduction and metabolism to favour nutrition and development of its juvenile stages. Parasite-regulated biosynthesis and mobilization of nitrogen metabolites determine a significant increase of host nutritional suitability. The aim of the present study was mainly to investigate the temporal changes of A. pisum amino acid pools, as affected by A. ervi parasitism, and to assess the role of the aphid bacterial endosymbiont Buchnera in determining the observed changes. In parasitized aphids, we observed a very significant increase in total free amino acids, compared with synchronous non-parasitized controls, starting from day 4 after parasitization (+51%). This trend culminated with more than doubling the control value (+152%) on day 6 after parasitization. However, a significant "parasitism" effect was observed only for 10 of the 28 amino acids detected. Tyrosine accumulation was the most prominent parasitoid-induced alteration, with a fourfold increase over control levels registered on day 6. In parasitized hosts, the amino acid biosynthetic capacity of Buchnera was unaltered, or even enhanced for the phenolic pool, and contributed greatly to the definition and maintainance of host free amino acid pools. The hypertyrosinemic syndrome was not dependent on food supply of the aromatic nucleus but was induced by parasitism, which likely enhanced the aromatic shuttle mediating phenylalanine transfer from bacteria to the host tissues, where tyrosine conversion occurs. This process is likely associated with a selective disruption of the host's functions requiring tyrosine, leading to the remarkable accumulation of this amino acid. The possible mechanisms determining these parasitism-induced host alterations, and their nutritional significance for the developing parasitoid larva, are discussed.

Journal Article↗
PubMed1984

Serotonin receptors in parasitic worms.

It is evident from the above review that during the last two decades a great deal of interest in investigating the action of serotonin in parasitic worms has been shown by parasitologists as well as by scientists from several other disciplines. What we have initially reported concerning the effect of serotonin on motility and carbohydrate metabolism of F. hepatica has been pursued on several other parasitic worms. The studies so far indicate that serotonin stimulates motility of every species tested among the phylum Platyhelminthes. The indoleamine also stimulates glycogenolysis in the few flatworm parasites that have been investigated. The information in nematodes is scanty and the role of serotonin in these parasites is still open for experimentation. Recent biochemical investigations on F. hepatica and S. mansoni demonstrated that serotonin and related compounds utilize a common class of receptors in plasma membrane particles which I designate as 'serotonin receptors'. These receptors are linked to an adenylate cyclase that catalyses the synthesis of the second messenger, cyclic 3',5'-AMP. Serotonin and its congeners increase the concentration of cyclic AMP in intact parasites whereas antagonists inhibit such an effect. Cyclic AMP stimulates glycogenolysis, glycolysis and some rate-limiting glycolytic enzymes. It activates a protein kinase that may be involved in activation of glycogen phosphorylase and phosphofructokinase. Serotonin-activated adenylate cyclase in S. mansoni is activated early in the life of the schistosomule. The possibility is discussed that the availability of cyclic AMP through serotonin activation in these parasites may be a prelude to the development processes that take place in the parasite. The different components of the serotonin-activated adenylate cyclase in the parasite are the same as those that have been previously described for the host. Binding characteristics of the receptors indicate that the receptors in F. hepatica appear to be different from those that have been described in the host. The discovery of these receptors and their differences from those in the host offer a new site which is amenable to pharmacological manipulation. The search for new agents that influence serotonin receptors in these parasites could be included in a strategy for the development of new chemotherapeutic agents against these parasites.

Adenylyl Cyclases↗
PubMed1991

Influence of pollution on parasites of aquatic animals.

We have tried to draw attention to an increasing body of evidence (from several publications) that parasites of fish might be useful indicators of pollution. Several types of pollutants, including domestic sewage, pesticides, polychlorinated biphenyls, heavy metals, pulp and paper effluents, petroleum aromatic hydrocarbons, acid rain, and others, are known to affect aquatic animals. Many of the latter are parasitized and, under natural environmental conditions, most fish parasites are believed to cause little or no harm. However, chronic exposure to pollutants over a period of time causes biochemical, physiological and behavioural host changes that ultimately can influence the prevalence and intensity of parasitism. Some of these changes include host nutrition, growth and reproduction. Macroscopic lesions might not always be apparent, but subtle disorders in several specific tissues and organs might occur. Pollutants might promote increased parasitism in aquatic animals, especially fish, by impairing the host's immune response or favouring the survival and reproduction of the intermediate hosts. Alternatively, decreased parasitism might ensue through toxicity of the pollutant to free-living stages and intermediate hosts or by alteration of the host's physiology. Experimental studies indicate that the numbers of ectoparasites such as trichodinid ciliates and monogeneans increase significantly on the gills following exposure to a pollutant, and this is supported by field data on other ciliates and monogeneans where evidence of pollution has been clearly demonstrated. There is also evidence that endoparasitic protozoons, such as myxozoons, microsporans and haematozoons, all of which are capable of proliferating in their hosts, increase substantially in prevalence and intensity when interacting with pollutants. The period of patency might also be prolonged in haematozoan infections. Most reports of pollution effects on endoparasites suggest increased parasitism in fish hosts. This also applies to fish living in areas which receive thermal effluents. Parasites might in turn enhance their hosts' susceptibility to pollutants, and information in support of this view is accumulating. Finally, immunosuppression represents one of the underlying mechanisms influencing increased parasitism. Thus, while published information suggests more than a casual connection between fish parasites and pollution, further research is needed to establish the cause-and-effect relationship and at the same time take cognizance of histopathological effects of the toxic agents and their concentrations in water. Areas for future research are recommended.

Animals↗
PubMed1997

Economics of gastrointestinal parasitism of cattle.

Understandably, cattle are raised for profit, as beef and/or dairy. Anything that negates that equation results in a loss to the producer and to the livestock economy. Thus, parasites negatively affect the economy of the industry. Worldwide, gastrointestinal nematode parasites, especially Ostertagia ostertagi, and those of the respiratory tract (Dictyocaulus viviparus) have a potentially major impact on herd health. In the past 10-15 years, anthelmintic (AH) drug development and the strategic use of AH have positively balanced the economic equation, so that overall, parasitism in cattle is often observed or determined to be subclinical or economical. Other control measures, such as better pasture management, are also being developed to enhance herd health and the cattle economy. The determination of the economic impact of parasitism has thus become less apparent, to the extent that measures, such as performance parameters, must be used to measure differences between treated and untreated animals or herds. These include weight gain, reproduction, lactation and forage use. To determine the effectiveness of control measures, field trials are designed to measure these parameters by the demonstration of improved performance. Because these trials are conducted in a competitive mode, results are often debated by competitors and by the scientific community because of study design. Variables must then be taken into consideration in the interpretation of results. It is now well known that, with the generation of new AH and appropriately-timed administration, parasitism of well-managed herds has been reduced to subclinical levels. Thus, we are now in the process of fine-tuning the positive effect of these control measures for enhanced production. Understandably, beef and dairy producers have 'production of high quality commodities' at a cost-effective level as a common goal. Successful cattlemen calculate expenditures and income by line item including veterinary expenses and cost and labor in administration of AH. Return is based on performance. Again, nematode parasites can disturb the equation enough to make production less profitable or even unprofitable. Most USA beef cattle producers believe that worm parasites do have an effect on cattle health and production so that 77% use AH and the market impact is that AH have become integrated into cattle herd health programs. However, to be most cost-effective, programs must be strategic but flexible with scheduling tailored for the region and the cattle operation. Other technologies should eventually provide rapid identification of worm populations by species and numbers and recognition of individual animal response to parasites and inheritance of that trait by their progeny. Computerized programs for analysis of seasonality of the epidemiology of gastrointestinal parasites and of herd performance could predict appropriate timing and cost benefit for control measures. Modes of AH administration are being developed which are more reliable and convenient in terms of delivery and labor. Control measures must also include better pasture management with less impact on the environment and to justify investment in land. In addition, successful producers are better educated, more cost-conscious, consumer-oriented, sensitive to the environment and attuned to the economics of parasitism.

Animals↗
PubMed1999

Cysteine protease inhibitors as chemotherapy for parasitic infections.

Analysis of the evolution, localization and biologic function of papain family cysteine proteases in metazoan and protozoan parasites has provided important and often surprising insights into the biochemistry and cellular function of this diverse enzyme family. Furthermore, the relative lack of redundancy of cysteine proteases in parasites compared to their mammalian hosts makes them attractive targets for the development of new antiparasitic chemotherapy. The treatment of experimental models of parasitic diseases with cysteine protease inhibitors has provided an important 'proof of concept' for the use of cysteine protease inhibitors in vivo. Evidence has now accumulated that cysteine protease inhibitors can selectively arrest replication of a microbial pathogen without untoward toxicity to the host. Furthermore, this can be achieved with reasonable dosing schedules and oral administration of the drug. Initial studies have confirmed the efficacy of cysteine protease inhibitors in treatment of Trypanosoma cruzi, Plasmodium falciparum and Leishmania major. Work on Trypanosoma brucei, the agent of African trypanosomiasis, is preliminary but also promising. Target validation studies have shown that biotinylated or radiolabeled irreversible inhibitors specifically bind to the cysteine protease targets thought to represent the major activity within the parasite. In the case of T. cruzi, the effect of inhibitors appears to be predominantly in blocking protease processing. Transfection studies using variant constructs have supported this model. Finally, the generation of null mutants for the multiple protease genes in Leishmania mexicana has provided the first genetic support for the key role of this enzyme family in parasite virulence. Safety studies in rodents and analysis of uptake of inhibitors by parasites and host cells suggest that the selectivity of inhibitors for the parasite targets may reside in the lack of redundancy of parasite proteases, the higher concentration of host proteases in intracellular compartments, and differential uptake of inhibitors by parasites. Attempts to elicit resistance to cysteine protease inhibitors in parasite cultures suggest that mechanisms of induced resistance are independent of resistance to the traditional antiparasitic agents. This suggests that cysteine protease inhibitors may provide an alternative to traditional therapy in drug-resistant organisms.

Animals↗
PubMed2006

Engineering broad root-knot resistance in transgenic plants by RNAi silencing of a conserved and essential root-knot nematode parasitism gene.

Secreted parasitism proteins encoded by parasitism genes expressed in esophageal gland cells mediate infection and parasitism of plants by root-knot nematodes (RKN). Parasitism gene 16D10 encodes a conserved RKN secretory peptide that stimulates root growth and functions as a ligand for a putative plant transcription factor. We used in vitro and in vivo RNA interference approaches to silence this parasitism gene in RKN and validate that the parasitism gene has an essential function in RKN parasitism of plants. Ingestion of 16D10 dsRNA in vitro silenced the target parasitism gene in RKN and resulted in reduced nematode infectivity. In vivo expression of 16D10 dsRNA in Arabidopsis resulted in resistance effective against the four major RKN species. Because no known natural resistance gene has this wide effective range of RKN resistance, bioengineering crops expressing dsRNA that silence target RKN parasitism genes to disrupt the parasitic process represents a viable and flexible means of developing novel durable RKN-resistant crops and could provide crops with unprecedented broad resistance to RKN.

Animals↗
PubMed2004

Host sex and local adaptation by parasites in a snail-trematode interaction.

One of the leading theories for the evolutionary stability of sex in eukaryotes relies on parasite-mediated selection against locally common host genotypes (the Red Queen hypothesis). As such, parasites would be expected to be better at infecting sympatric host populations than allopatric host populations. Here we examined all published and unpublished infection experiments on a snail-trematode system (Potamopyrgus antipodarum and Microphallus sp., respectively). A meta-analysis demonstrated significant local adaptation by the parasite, and a variance components analysis showed that the variance due to the host-parasite interaction far exceeded the variance due to the main effects of host source and parasite source. The meta-analysis also indicated that asexual host populations were more resistant to allopatric sources of parasites than were (mostly) sexual host populations, but we found no significant differences among parasite populations in the strength of local adaptation. This result suggests that triploid asexual snails are more resistant to remote sources of parasites, but the parasite has, through coevolution, overcome the difference. Finally, we found that the degree of local adaptation did not depend on the genetic distance among host populations. Taken together, the results demonstrate that the parasites are adapted, on average, to infecting their local host populations and suggest that they may be a factor in selecting against common host genotypes in natural populations.

Adaptation, Physiological↗
PubMed1991

Nosocomial transmission and infection control aspects of parasitic and ectoparasitic diseases. Part III. Ectoparasites/summary and conclusions.

As a rule, both the standard of hygiene and sanitation prevalent in hospitals in the United States and the rarity of parasitic diseases compared to viral, bacterial, and fungal infections, reduce the hazard of nosocomial acquisition of parasites to relatively trivial levels. However, abetted by the resultant low index of suspicion on the part of clinical staff, certain parasitic microorganisms may at times cause significant morbidity and even mortality in both normal and immunocompromised patients, as summarized in this review. Also, the nosocomial acquisition of parasites may be somewhat underappreciated because the incubation period for clinical illness may be days to weeks and thus a hospital-acquired infection may not be recognized as such, particularly if the parasite is endemic locally. Parasitic diseases have been a much more significant problem in certain special facilities, such as custodial institutions for the mentally ill or retarded, where crowding, poor environmental sanitation, and low levels of personal hygiene have in the past allowed the rapid dissemination and endemic occurrence of a large variety of parasitic infections. It is likely that nosocomial transmission of parasites may be an even greater problem in some hospitals in the tropics, where strict hygienic standards are costly or otherwise more difficult to maintain, and where often an increased proportion of the patient population harbors one or more parasites. However, the exact magnitude of the problem in tropical hospitals is also more difficult to determine because nosocomial acquisition of a parasitic infection may not be distinguished easily versus exogenous infection or reactivation of latent infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗