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PubMed1984

Activation of the alternative complement pathway by Leishmania promastigotes: parasite lysis and attachment to macrophages.

When exposed to normal human or guinea pig sera, promastigotes of Leishmania enriettii and L. tropica activate the complement cascade by the alternative pathway and fix C3 on their surfaces. In high (25%) serum concentrations, the result of complement activation is parasite lysis. At lower concentrations (4%), complement fixation results in enhanced parasite binding and uptake into murine peritoneal macrophages. Parasites are lysed in normal guinea pig, C4-deficient guinea pig, normal human, and C2-deficient human sera when they are incubated at 37 degrees C for 30 min. Fetal calf and normal mouse sera are poorly lytic. Lysis requires Mg++ but not Ca++, is mediated by heat labile (56 degrees C, 30 min) component(s), and does not occur when the incubations are maintained at 4 degrees C. Guinea pig serum preadsorbed with promastigotes of L. tropica in EDTA at 4 degrees C for 30 min is fully lytic. Immunofluorescence studies with anti-C3 antibodies show that under these conditions C3 is deposited on the surface of the parasite. The serum-dependent binding of parasites to macrophages is also mediated by heat-labile, nonadsorbable factor(s) present in normal guinea pig and mouse sera, as well as C2-deficient and C4-deficient sera. The serum-dependent macrophage recognition mechanism is trypsin sensitive but relatively resistant to chymotrypsin. Parasites but not macrophages can be presensitized at room temperature with low levels (8%) of serum to enhance their binding to macrophages. Presensitization does not occur at 4 degrees C. These results show that Leishmania promastigotes of several species can fix complement by activating the alternative complement pathway. This may then result either in parasite lysis or in an accelerated uptake of the parasite into phagocytic cells. In vivo, the biologic outcome of infection may reflect a balance between extracellular lysis and enhanced uptake into phagocytic cells.

Animals↗

PubMed1984

Induction of crisis forms in the human malaria parasite Plasmodium falciparum by gamma-interferon-activated, monocyte-derived macrophages.

Previous investigations on the mechanism by which the host mounts an immune response against the human malaria parasite Plasmodium falciparum have not resolved whether cell-mediated responses, in the absence of circulating anti-Plasmodial antibodies, can effect the destruction of the intraerythrocytic parasite. We report that the intraerythrocytic parasite P. falciparum is lethally susceptible to the imposition of oxygen-dependent and oxygen-independent factor(s) released by interferon-gamma-activated, monocyte-derived human macrophages. In addition, trophozoite-schizont stage intraerythrocytic parasites were killed on exposure to small amounts of H2O2 generated in cell-free enzyme assays. Although parasiticidal activity was markedly enhanced by the addition of lactoperoxidase and KI, killing was abrogated by the addition of catalase. The ability of freshly isolated human monocytes, monocyte-derived macrophages (MDM), and lymphokine-activated MDM to kill or inhibit the growth and multiplication of the malaria parasites was assessed. Parasites were killed when exposed to monocytes or lymphokine-activated MDM, but not when exposed to nonactivated macrophages. The capacity to activate MDM for microbicidal activity was abrogated on neutralization of crude lymphokines or recombinant interferon-gamma with a monoclonal antibody prepared against interferon-gamma. The intraerythrocytic parasites surviving the cytotoxicity assay were inhibited in their development and appeared to be degenerating, a characteristic of "crisis" forms. Killing of P. falciparum correlated positively with the magnitude of the oxidative response, as evidenced by the reduction of nitroblue tetrazolium to formazan in the mononuclear phagocytes, and by the detection of secreted H2O2. Of particular interest was the observation that only the later developing stage of the intracellular parasite triggered the respiratory burst in the absence of antibody. A role for oxygen-independent parasiticidal factors was suggested by the finding that lymphokine-activated macrophages from a patient with chronic granulomatous disease were able to partially inhibit the growth of P. falciparum, although oxidative metabolism in these cells was impaired.

Erythrocytes↗

PubMed1981

Babesia divergens: combination of dead and live parasites in an irradiated vaccine.

Two experiments were carried out to investigate the hypothesis that the protective effect of an irradiated Babesia divergens vaccine was due to the combined inoculation of large numbers of dead parasites and small number of live ones. In the first experiment it was demonstrated that animals receiving 10(8) parasites irradiated at 25 kilorads had more severe B divergens reactions than animals in a previous experiment which had received 10(10) parasites irradiated at 24, 28 or 32 kilorads. In the second experiment it was shown that the simultaneous inoculation of 10(10) parasites killed by irradiation at 50 kilorads and 10(8) parasites irradiated at 25 kilorads resulted in the suppression of the relatively severe reactions induced by inoculation of the 25 kilorad-irradiated parasites alone. It was also shown that the simultaneous inoculation of 10(10) parasites irradiated at 50 kilorads and 10(4) live parasites similarly suppressed the anticipated reactions of the calves. These results indicated that the hypothesis was correct under the conditions of the experiment.

Animals↗

PubMed1993

Morphological and physiological consequences of parasites encysted in the bulbus arteriosus of an estuarine fish, the sheepshead minnow, Cyprinodon variegatus.

The contribution of parasites to host population regulation is undefinable without knowledge of parasite effects on individual host performance and survival. Effects are best determined by examining performance of differentially parasitized hosts under the varying environmental conditions that characterize the host's habitat. The sheepshead minnow, Cyprinodon variegatus, an estuarine fish, is heavily parasitized in the bulbus arteriosus by the heterophyid trematode Ascocotyle pachycystis in semi-enclosed shallow bodies of water in northwestern Florida. Laboratory experiments were conducted to examine the morphological and physiological effects of parasitization of these fish. Differentially parasitized fish were compared for differences in ventricle weight and swimming performance. Parasitized fish ventricles were hypertrophied due to mechanical blockage of normal blood flow by metacercariae in the bulbus. Swimming performance generally was reduced by the presence of parasites, which had their most significant negative effect at cold temperatures and low dissolved oxygen levels.

Analysis of Variance↗

PubMed1997

Evolutionary constraints on population structure: the parasites of Fundulus zebrinus (Pisces:Cyprinodontidae) in the South Platte River of Nebraska.

Population and community descriptor values (parasites per host, prevalence per parasite species, variance/mean ratios, species density, and diversity indices) for the 7-species parasite community of 61 relatively homogeneous samples of Fundulus zebrinus (Pisces: Cyprinodontidae) in the South Platte River of Nebraska, U.S.A., taken over a 14-yr period, are reported. South Platte River streamflow fluctuates over 2 orders of magnitude on several time scales-monthly, annually, and over multiple year wet-dry cycles. Relatively homogeneous sampling of a single host species with several parasite species provided a system that allowed assessment of the contribution of evolved parasite life cycles to population structure in an everchanging environment. No significant negative species-to-species associations were observed. Species abundance, order of abundance, and diversity were affected most strongly by streamflow, with high water reducing prevalence and abundance of larval trematode parasites. Each parasite species had its characteristic long- and short-term patterns of variation in population descriptor values, with mostly long-term stability superimposed on sometimes extreme short-term fluctuations of descriptor values. The differences in these characteristic patterns were considered products primarily of the evolved life cycle traits and transmission mechanisms operating in the common fluctuating environment. The parasite community as a whole showed resilience, returning to preperturbation diversity following extended periods of high water.

Animals↗

PubMed1997

Botfly (Diptera:Oestridae) parasitism of Ord's kangaroo rats (Dipodomys ordii) at Suffield National Wildlife Area, Alberta, Canada.

During field study of Ord's kangaroo rat (Dipodomys ordii) at Suffield National Wildlife Area, Alberta, Canada, a high prevalence of parasitism by botfly (Diptera: Oestridae) larvae was observed. Botflies have not previously been documented as parasites of kangaroo rats. Botfly parasitism could have a significant impact on the growth, survival, and reproduction of Ord's kangaroo rat, which is considered a vulnerable species in Canada. Therefore, it is important to investigate how botfly parasitism varies with season and with gender or age of host. In 1995, 525 individual kangaroo rats were caught by nightlighting and live trapping for a total of 952 capture records. Upon capture, each kangaroo rat was ear-tagged and thoroughly examined for parasites and wounds. Third-instar botfly (Cuterebra polita) larvae were observed in kangaroo rats between 16 June and 23 August. Prevalence was 34% based on 454 kangaroo rats sampled during that time, whereas the mean intensity was 2.3 larvae per infested host (n = 156, range = 1-11). In contrast to some other studies of botfly parasitism of rodents, there were no gender or age biases in either prevalence or intensity of infestation. The index of dispersion was 2.8, indicating that the parasites were aggregated in hosts. Botfly parasitism could be an important factor affecting northern populations of kangaroo rats; future investigations into the potential effects of botfly larvae on host fitness are warranted.

Alberta↗

PubMed1997

Vaccine development against Theileria parasite.

Bovine piroplasmosis caused by Theileria sergenti is a major cause of economical loss in grazing cattle in Japan. We found that parasite stocks and isolates consist of genetically and antigenically mixed population. To differentiate parasite populations bearing 2 allelic forms of p32, an immunodominant piroplasm surface protein, 2 sets of oligonucleotide primers were designed to amplify either of the 2 alleles by polymerase chain reaction (PCR). By using this allele-specific PCR, we found that the majority of T. sergenti-infected calves in Japan harbored mixed parasite populations with C and I type parasites. Amino acid sequence of p32 contains Lys-Glu-Lys (KEK) motif which is one of tripeptide necessary for malaria parasite to invade erythrocytes. We produced 2 vaccine candidates, recombinant baculovirus p32 and synthetic peptide containing KEK motif. Immunization of either recombinant p32 or synthetic peptide containing a KEK sequence with adjuvant resulted in low parasitemia and reduced the clinical symptoms compared to control calves. Interestingly, parasites with a p32 allelic form corresponding to one used as the immunogen were suppressed. Therefore, a cocktail vaccine containing KEK peptides derived from C and I type parasites is desired for control Theileria parasite infection in Japan.

Amino Acid Sequence↗

PubMed1998

Colonization and seasonality of goby (Gobiidae, Teleostei) parasites from the southwestern Baltic Sea.

A comparative parasitology study of gobiid fishes from two sites on the western Baltic Sea was done to get information on the quality of the respective environments. The parameters used were the infracommunity, the species numbers and abundance with respect to the size classes of the hosts, and the abundance with respect to the seasons. The hosts, Gobius niger, Gobiusculus flavescens, Pomatoschistus minutus, and P. pictus, were caught at Blank Eck (Kiel Bight) and Dahmeshöved (Lübeck Bight) during 1992 and 1993. The infracommunities of Dahmeshöved attained higher rates of prevalence of helminth parasites than did those of Blank Eck, as was valid in all host specimens harboring one or two parasite species. The group bearing three parasite species was present in Dahmeshöved but absent in Blank Eck. Parasite species numbers, which were similar in the two sites, increased from the smallest to the largest hosts but changed with growth. With one exception, this result is also valid for the abundance, which clearly differed between the hosts and between the sites. Whereas species numbers as well as abundance rates were low in spring, they increased in summer. The results reveal that the composition of infracommunities depends on the local parasite fauna and on the strength of general host defense mechanisms, whereas that of the component community is dependent on the susceptibility of hosts to single parasite species and on the density of intermediate parasite stages. This is also the reason for the stronger infestation of hosts from Dahmeshöved as opposed to those from Blank Eck, where the degree of eutrophication is lower and, therefore, fewer herbivorous intermediate hosts can exist.

Animals↗

PubMed2005

Parasites and salinity: costly tradeoffs in a threatened species.

Parasites and environmental conditions can have direct and indirect effects on individuals. We explore the relationship between salinity and parasites in an endemic New Mexico State threatened fish, the White Sands pupfish (Cyprinodon tularosa). Spatial variation in salinity limits the distribution of the endemic springsnail (Juturnia tularosae) within Salt Creek, a small desert stream. The springsnail is the presumed intermediate host for trematodes that infect the White Sands pupfish, and trematode prevalence and intensity in pupfish are positively associated with the springsnail. Salinity and parasites both have negative impacts on pupfish, but in areas of high salinity, pupfish can effectively escape parasites. Pupfish trematodes were absent from sites lacking snails. At the upstream site, the absence of parasites and lower variance in salinity were correlated with larger pupfish that were in better condition than pupfish at either the middle or lower sites. Springsnails were present in the middle section, an area with moderate salinity, and all pupfish had trematodes (median abundance 847 trematodes/fish). Lipid levels and condition were lowest in fish from the middle site. Additionally, fewer older fish indicated an increased mortality rate. At the lower site, springsnails were absent due to high salinity; pupfish trematode abundance was much lower (six trematodes/fish), and fish condition was intermediate. An additional experiment revealed that snail activity and survival were significantly reduced at high salinities commonly present at the lower site. Although both high salinity and parasites significantly affect pupfish, parasites might be more detrimental.

Animals↗

PubMed1993

A multimedia relational database program for parasite identification.

Parasites are responsible for human and animal diseases causing suffering and economic loss all over the world. Parasite identification is an important step in treating and combating parasitic diseases. This task can be assisted by computer programs. Until now computer based systems for parasite identification were fixed tree-decision programs which had no updating or expansion capacity and no ability for optimal searching algorithms. A new program was developed by using a multimedia relational database management system with a graphical environment. This program can incorporate expert knowledge in its relational structure and identify the parasites by using its structured query language. Also, the program has the ability for partial identification by presenting the parasites that match the available incomplete information. In addition, the program can handle images and sound to present pictures and relevant information on the identified parasites. The advantages of the new program are its friendly graphical user interface and its unlimited capacity to incorporate new knowledge.

Algorithms↗

PubMed1989

Molecular vaccines against animal parasites.

Vaccines against parasites have been significantly more difficult to develop than vaccines for other infectious agents. However much has been published within the very recent past which indicates that it is not only possible to induce protective immune responses to a broad range of parasites of veterinary importance with subunit materials but it appears that cross-isolate and cross-species immunogens may be obtainable. Advances in molecular immunology now provide technical approaches to vaccine design which directly address the question of improving the immunogenicity of parasite vaccines and the very wide potential range of prospective live vectors for recombinant vaccine antigens help to ensure the availability of practical commercial vaccine vectors for the future. From the technical-scientific aspect therefore the feasibility for developing molecular parasite vaccines for animal health is sound. On the commercial side, the need to keep discovering novel and effective parasiticidal drugs because of resistance development presents a major financial and research burden. Growing concerns on drug residues and environmental issues mitigates in favour of controlling parasitic diseases by biological methods among which vaccines would appear to be pre-eminently suitable. It is conceivable that we are now coming to the end of the era in which animal parasites are controlled very well by prophylactic chemotherapy and slowly moving into an era where vaccination will prevail. The deployment of molecular parasite vaccines in animal health can be envisaged within five years.

Animals↗

PubMed2005

Infection of naïve, free-living brushtail possums (Trichosurus vulpecula) with the nematode parasite Parastrongyloides trichosuri and its subsequent spread.

Despite the importance of spatial processes in host-parasite interactions, parasite dispersal has been the subject of few experimental studies. Introduced marsupial common brushtail possums (Trichosurus vulpecula) are a major environmental and agricultural pest in New Zealand. Parastrongyloides trichosuri, an intestinal rhabdiasoid nematode parasite specific to possums, is being evaluated as a self-disseminating delivery system for engineered fertility control vaccines. This study addressed whether an artificial infection could be established in a naïve, free-living possum population, by measuring the post-release dynamics of possum-parasite interactions at the release site, and by following the spread of the parasite into surrounding possum populations. Infection was established efficiently by applying infective larvae to the skin of possums on a single occasion. All experimentally infected possums recaptured 3 weeks after infection had parasite eggs in their faeces. Over the subsequent 2.5 years, infection spread steadily over an area of about 6000 ha. Infection persisted at the original release site for the 3.5 years of the study and at a nearby site infected by natural spread for more than 3 years. Seasonal changes in faecal egg counts were similar at the two sites. The rapid establishment of the parasite and its spread provide additional support for its ongoing development as a vaccine delivery system.

Animals↗

PubMed2005

Speciation in parasites: a population genetics approach.

Parasite speciation and host-parasite coevolution should be studied at both macroevolutionary and microevolutionary levels. Studies on a macroevolutionary scale provide an essential framework for understanding the origins of parasite lineages and the patterns of diversification. However, because coevolutionary interactions can be highly divergent across time and space, it is important to quantify and compare the phylogeographic variation in both the host and the parasite throughout their geographical range. Furthermore, to evaluate demographic parameters that are relevant to population genetics structure, such as effective population size and parasite transmission, parasite populations must be studied using neutral genetic markers. Previous emphasis on larger-scale studies means that the connection between microevolutionary and macroevolutionary events is poorly explored. In this article, we focus on the spatial fragmentation of parasites and the population genetics processes behind their diversification in an effort to bridge the micro- and macro-scales.

Animals↗

PubMed2006

Steroid hormone related male biased parasitism in chamois, Rupicapra rupicapra rupicapra.

Parasites are linked with their host in a trophic interaction with implications for both hosts and parasites. Interaction stretches from the host's immune response to the structuring of communities and the evolution of biodiversity. As in many species sex determines life history strategy, response to parasites may be sex-specific. Males of vertebrate species tend to exhibit higher rates of parasites than females. Sex-associated hormones may influence immunocompetence and are hypothesised to lead to this bias. In a field study, we tested the prediction of male biased parasitism (MBP) in free ranging chamois (Rupicapra rupicapra rupicapra), which are infested intensely by gastrointestinal and lung helminths. We further investigated sex differences in faecal androgen (testosterone and epiandrosterone), cortisol and oestrogen metabolites using enzyme immunoassays (EIA) to evaluate the impact of these hormones on sex dependent parasite susceptibility. Non-invasive methods were used and the study was conducted throughout a year to detect seasonal patterns. Hormone levels and parasite counts varied significantly throughout the year. Male chamois had a higher output of gastrointestinal eggs and lungworm larvae when compared to females. The hypothesis of MBP originating in sex related hormone levels was confirmed for the elevated output of lungworm larvae, but not for the gastrointestinal nematodes. The faecal output of lungworm larvae was significantly correlated with androgen and cortisol metabolite levels. Our study shows that sex differences in steroid levels play an important role to explain MBP, although they alone cannot fully explain the phenomenon.

Analysis of Variance↗

PubMed2003

Pattern selection in a cooperative biochemical in vitro amplification system: the role of parasites.

Previously, numerical simulations have shown that evolving systems can be stabilized against emerging parasites by pattern formation in spatially extended flow reactors. Hence, it can be argued that pattern formation is a prerequisite for any experimental investigation of the biochemical evolution of cooperative function. Here, we study a model of an experimental biochemical system for the cooperative in vitro amplification of DNA strands and show that emerging parasites can induce a complex pattern formation even when no pattern formation occurs without parasites. In an adiabatic approximation where the cooperative amplification reaction is assumed to adapt fast to slowly emerging parasites, the parasite concentration itself acts as a Steuer parameter for the selection of various complex patterns. Without such an adiabatic approximation only transient patterns emerge. As any species can grow for very low concentrations, the parasite is able to infect the entire reactor and the system is finally diluted out. In the experimental biochemical system, however, the species are individual molecules and the growth of spatially separated, non-infected regions becomes feasible. Hence a cutoff threshold for the minimal concentration is applied. In these simulations the otherwise lethal infection by parasites induces the formation of spatiotemporal spirals, and this spatial structure help the host and parasitoid species to survive together. These theoretical results describe an inherent property of cooperative reactions and have an important impact on experimental investigations on the molecular evolution and complex function in spatially extended reactors. Since the formation of the complex pattern is restricted either to a rather large cutoff value or a special choice of the kinetic parameters, we, however, conclude that the persistence of evolving cooperative amplification is not possible in a simple reaction-diffusion reactor. Experimental set-ups with patchy environments, e.g. biomolecular amplification in coupled microstructured flow chambers or in microemulsion, are eligible candidates for the observation of such a self-organized pattern selection.

Animals↗

PubMed2002

Parasitism at the ecosystem level in the Baltic Sea.

The Baltic Sea is characterized by organisms that can tolerate brackish water. Because of the Sea's history during glacial times, its flora and fauna (and also their parasites) can be traced to marine, freshwater and genuine brackish elements beside glacial relics. Snails, planktonic copepods, benthic amphipods and isopods are important intermediate hosts of diverse helminths; in addition polychaetes, bivalves and fishes may also act as final hosts. The most important final hosts, beside fishes, were seals and birds; these were able to disperse the parasites over the whole of the Baltic. Decreasing salinity from west to east limits the distribution of many parasites. Several marine and genuine brackish water species have almost spread over the whole Baltic. Freshwater species, however, have a lower tolerance than marine species and are only rarely found in the western part. A serious problem in the Baltic is eutrophication which can lead to massive abundances of generalist parasites, in host populations as well as host individuals. The final stage of this influence can cause a general decrease of host abundance and, as a consequence, of all kinds of parasites, due to oxygen deficiency. In comparison with the species spectrum of other brackish waters in Europe, the Baltic presents some endemic parasites as well as sharing parasite species with the Mediterranean and even the Black Sea.

Animals↗

PubMed2006

Avoiding bias in parasite excretion estimates: the effect of sampling time and type of faeces.

The study of host-parasite relationships usually requires reliable estimates of parasite intensity, which is often estimated from parasite propagule concentration in faeces. However, parasite excretion in faeces may be subject to variation due to endogenous or exogenous factors that must be identified to obtain reliable results. We analysed the effect of the hour of sample collection on propagule counts of 2 intestinal parasites infecting the red-legged partridge: the capillarid nematode Aonchoteca caudinflata and coccidia of the genus Eimeria (Protozoa). Also, we test whether there are differences in propagule counts between caecal and intestinal faeces. Individual faecal samples from infected birds were collected daily at 4 different hours during several days. The hour of the day exerted a very strong effect on propagule counts, excretion of both types of parasites showing a clear and constant increase from dawn to dusk. Also, capillarid eggs were more abundant in intestinal than in caecal faeces, whereas the inverse pattern was found for coccidian oocysts. Standardization of the hour of sample collection or statistical control of this variable is recommendable to prevent bias. Similarly, in bird species with long caeca, consistent collection of one type of faeces may avoid significant errors in parasite burden estimates.

Animals↗

PubMed2004

An obligate brood parasite trapped in the intraspecific arms race of its hosts.

Reciprocal selection pressures often lead to close and adaptive matching of traits in coevolved species. A failure of one species to match the evolutionary trajectories of another is often attributed to evolutionary lags or to differing selection pressures across a geographic mosaic. Here we show that mismatches in adaptation of interacting species--an obligate brood parasitic duck and each of its two main hosts--are best explained by the evolutionary dynamics within the host species. Rejection of the brood parasite's eggs was common by both hosts, despite a lack of detectable cost of parasitism to the hosts. Egg rejection markedly reduced parasite fitness, but egg mimicry experiments revealed no phenotypic natural selection for more mimetic parasitic eggs. These paradoxical results were resolved by the discovery of intraspecific brood parasitism and conspecific egg rejection within the hosts themselves. The apparent arms race between species seems instead to be an incidental by-product of within-species conflict, with little recourse for evolutionary response by the parasite.

Adaptation, Physiological↗