Showing papers in "Parasitology in 2002"

Parasitism, community structure and biodiversity in intertidal ecosystems.

Abstract: There is mounting evidence that parasites can influence the composition and structure of natural animal communities. In spite of this, it is difficult to assess just how important parasitism is for community structure because very few studies have been designed specifically to address the role of parasites at the community level, no doubt because it is difficult to manipulate the abundance of parasites in field experiments. Here, we bring together a large amount of published information on parasitism in intertidal communities to highlight the potential influence of parasites on the structure and biodiversity of these communities. We first review the impact of metazoan parasites on the survival, reproduction, growth and behaviour of intertidal invertebrates, from both rocky shores and soft-sediment flats. Published evidence suggests that the impact of parasites on individuals is often severe, though their effects at the population level are dependent on prevalence and intensity of infection. We then put this information together in a discussion of the impact of parasitism at the community level. We emphasize two ways in which parasites can modify the structure of intertidal communities. First, the direct impact of parasites on the abundance of key host species can decrease the importance of these hosts in competition or predator-prey interactions with other species. Second, the indirect effects of parasites on the behaviour of their hosts, e.g. burrowing ability or spatial distribution within the intertidal zone, can cause changes to various features of the habitat for other intertidal species, leading to their greater settlement success or to their local disappearance. Our synthesis allows specific predictions to be made regarding the potential impact of parasites in certain intertidal systems, and suggests that parasites must be included in future community studies and food web models of intertidal ecosystems.

Food webs and the transmission of parasites to marine fish

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

Parasites and marine invasions

Abstract: Introduced marine species are a major environmental and economic problem. The rate of these biological invasions has substantially increased in recent years due to the globalization of the world's economies. The damage caused by invasive species is often a result of the higher densities and larger sizes they attain compared to where they are native. A prominent hypothesis explaining the success of introduced species is that they are relatively free of the effects of natural enemies. Most notably, they may encounter fewer parasites in their introduced range compared to their native range. Parasites are ubiquitous and pervasive in marine systems, yet their role in marine invasions is relatively unexplored. Although data on parasites of marine organisms exist, the extent to which parasites can mediate marine invasions, or the extent to which invasive parasites and pathogens are responsible for infecting or potentially decimating native marine species have not been examined. In this review, we present a theoretical framework to model invasion success and examine the evidence for a relationship between parasite presence and the success of introduced marine species. For this, we compare the prevalence and species richness of parasites in several introduced populations of marine species with populations where they are native. We also discuss the potential impacts of introduced marine parasites on native ecosystems.

The role of promastigote secretory gel in the origin and transmission of the infective stage of Leishmania mexicana by the sandfly Lutzomyia longipalpis

Abstract: Transmission of leishmaniasis is effected by a specific developmental stage, the metacyclic promastigote. The precursors of metacyclic promastigotes were a distinct subpopulation of parasites, identified for the first time as a new stage in the life-cycle and named leptomonad promastigotes. Microdissection of infected sandflies into 4 midgut regions and foregut allowed precursor-product relationships to be established for amastigote-procyclic promastigote, procyclic-nectomonad promastigote, nectomonad-leptomonad promastigote and leptomonad-metacyclic promastigote developmental switches. Metacyclic promastigotes occurred mainly in the thoracic midgut and cardia, coincident with the accumulation of a promastigote secretory gel (PSG) plug in these anterior regions. The gel-like plug was isolated from flies with mature infections and found to contain predominantly leptomonad promastigotes. The PSG plug also contained the majority (75%) of the total metacyclic promastigote population in the sandflies, which were concentrated at the anterior pole. The PSG plug was found to be the main site of metacyclogenesis, and acted as a reservoir of leptomonad promastigotes from which metacyclic forms differentiated and migrated forward to promote the infective potential of the fly. The PSG plug occluded and distorted the midgut, forcing the stomodeal valve open and affecting the feeding success of the sandflies, such that they experienced difficulty in taking a full meal. Collectively, these data support the role of the PSG in the transmission of leishmaniasis, by conditioning the midgut environment for metacyclogenesis and altering the feeding ability of infected sandflies.

Parasites as biological tags in population studies of marine organisms: an update

Abstract: This paper reviews the work published over the past decade on the use of parasites as biological tags in population studies of marine fish, mammals and invertebrates. Fish hosts are considered in taxonomic and ecological groups as follows: demersal, anadromous, small pelagic, large pelagic and elasmobranch. Most studies were carried out on demersal fish, particularly on members of the genera Merluccius (hake), Sebastes (rockfish) and on Atlantic cod Gadus morhua L., but Pacific salmonids and small pelagic fish of the genus Trachurus are also well-represented. A current multidisciplinary study of the population biology of horse mackerel Trachurus trachurus in European waters, which includes the use of parasites as tags, is described. Two studies recognize the potential for using parasites as tags for cetaceans but, in spite of the considerable potential for this approach in population studies of elasmobranchs, no original study has been carried out on this group for over ten years. Studies of parasites as tags for marine invertebrates have concentrated on squid. Recent trends in the use of parasites as biological tags for marine hosts are discussed.

Molecular and morphological characterization of Echinococcus granulosus of human and animal origin in Iran

Abstract: Iran is an important endemic focus of cystic hydatid disease (CHD) where several species of intermediate host are commonly infected with Echinococcus granulosus. Isolates of E. granulosus were collected from humans and other animals from different geographical areas of Iran and characterized using both DNA (PCR-RFLP of ITS1) and morphological criteria (metacestode rostellar hook dimensions). The sheep and camel strains/genotypes were shown to occur in Iran. The sheep strain was shown to be the most common genotype of E. granulosus affecting sheep, cattle, goats and occasionally camels. The majority of camels were infected with the camel genotype as were 3 of 33 human cases. This is the first time that cases of CHD in humans have been identified in an area where a transmission cycle for the camel genotype exists. In addition, the camel genotype was found to cause infection in both sheep and cattle. Results also demonstrated that both sheep and camel strains can be readily differentiated on the basis of hook morphology alone.

A review of the population biology and host-parasite interactions of the sea louse Lepeophtheirus salmonis (Copepoda: Caligidae).

Abstract: Lepeophtheirus salmonis is a specific parasite of salmonids that occurs in the Atlantic and Pacific Oceans. When infestations are heavy fish mortality can occur although the factors that are responsible for causing epizootics, especially in wild salmonid populations are still largely unknown. Over the past 20 years this parasite has caused significant economic losses in farmed salmon production and possibly in wild salmonid populations locally. Understanding the connectivity between populations is crucial to an understanding of the epidemiology of infections and for management of infections in aquaculture. Data from genetics, pesticide resistance, larval dispersal models and spatial and temporal patterns of infestation in wild and farmed hosts suggests a spatially highly structured metapopulation the components of which have different levels of connectivity, probabilities of extinction and influence on the development of local infestations. The population structure is defined mainly by the dispersal dynamics of the planktonic stages and the behaviour of the host. Until recently virtually nothing was known about the relationship between the parasite and the host, or how the host may influence lice at local or population level. Typically, impacts on the host have usually been reported in terms of pathological lesions caused by attachment and feeding of the adult stages, as well as localised mild epithelial responses to juvenile attachment. However many studies report pathology associated with severe infestation. Recent new studies on the host-parasite interactions of L. salmonis have shown that this parasite induces stress-related responses systemically in the host skin and gills and that the stress response and immune systems are modulated. In the second part of this review, these new studies are presented, together with results from other host-parasite model systems where data for caligid sea lice are missing. One of the most revealing methods reported recently is the application of a net confinement stressor to examine modulation of the stress response and immune system of the host fish. This approach has shown that although until now, infective stages of L. salmonis were not thought to affect the host, they do induce systematic effects in the host that result in a stress response and modulated immune system. Host-parasite interactions affecting these stress responses and the immune system may be key factors in facilitating epizootics by reducing the host's ability to reject the parasites, as well as reducing disease resistance under some environmental conditions. The host-parasite interaction therefore needs to be incorporated into any model of population structure and dynamics.

A phylogenetic hypothesis for the distribution of two genotypes of the pig tapeworm Taenia solium worldwide.

Abstract: Genetic polymorphism was determined among 13 isolates of Taenia solium from various regions using PCR-amplified sequences of 2 mitochondrial genes: cytochrome c oxidase subunit 1 and cytochrome b. The 2 phylogenies obtained were similar to each other regardless of the genes examined. The isolates from Asia (China, Thailand, Irian Jaya and India) formed a single cluster, whereas the isolates from Latin America (Mexico, Peru, Ecuador, Bolivia and Brazil) combined with those from Africa (Tanzania, Mozambique and Cameroon) to form an additional cluster. These results and historical data of swine domestication, distribution of pigs and colonization suggest that T. solium was introduced recently into Latin America and Africa from different regions of Europe during the colonial age, which started 500 years ago, and that the tapeworm of another origin independently spread in Asian countries.

Spatial and temporal aspects of urban transmission of Echinococcus multilocularis.

Abstract: High prevalences of Echinococcus multilocularis have been reported from foxes of the city of Zurich, Switzerland. In order to characterize transmission in urban areas, a coproantigen ELISA was evaluated for diagnosing the infection in fox faecal samples collected in the environment. In addition, trapped rodents were investigated for the presence of metacestodes. Faecal samples could reliably be classified as being of fox origin by assessing physical properties as shown by the different parasite spectra of putative fox and dog faecal specimens. From the total of 604 tested putative fox faecal samples 156 (25.8%) were positive in the ELISA with a distinct increase in the proportion of positive samples from the urban to the periurban zone. Furthermore, samples collected in the border zone had significantly more coproantigen-positive results during winter. Prevalence of E. multilocularis in rodents was 9.1% (81/889) for Arvicola terrestris (with 3.5% of the animals harbouring between 14 and 244400 protoscoleces) and 2.4% (2/83) for Clethrionomys glareolus. E. multilocularis-infected A. terrestris were found in 9 of 10 trapping sites in the border zone. The high infection pressure in the periphery of urban areas might pose a risk for infection with E. multilocularis for both domestic carnivores as well as for urban inhabitants. Interventions into the cycle aiming at reducing the infection pressure should therefore focus on these areas.

Value of two PCR methods for the diagnosis of canine visceral leishmaniasis and the detection of asymptomatic carriers.

Abstract: The value of 2 PCR methods, targeting genomic and kinetoplast minicircle DNA respectively, was investigated for both diagnosis and prevalence studies of canine visceral leishmaniasis (CVL). The first method (R) was 5000-fold less sensitive than the second (method KRV). Both were tested for diagnosis of CVL in 44 sick dogs with confirmed disease using different biological samples. Method R was highly efficient when using invasive samples, but the use of method KRV proved necessary for a 100% sensitive diagnosis using peripheral blood. This method was applied to peripheral blood and skin samples in 263 dogs during a mass survey in the Cevennes focus. PCR was compared to serology and all results were analysed according to clinical status. The 'CVL-infection' prevalence was found to be 79.8% by PCR compared with 29.6% by serology: 89.4% of symptomatic and 65.2% of asymptomatic dogs harboured parasites in peripheral blood. This study confirms the high prevalence of asymptomatic carriers of Leishmania. In total, for the diagnosis of CVL in sick dogs, method R is recommended in view of its 100% positive predictive value (compared with 30% for method KRV). A strategy best adapted for prevalence surveys might combine serology and highly sensitive PCR on peripheral blood.

Population dynamics of untreated Plasmodium falciparum malaria within the adult human host during the expansion phase of the infection

Abstract: A retrospective analysis was performed of parasite count data recorded from the first 7 days of blood or mosquito transmitted Plasmodium falciparum infections given for the treatment of neurosyphilis in the USA before 1963. The objective of this study was to characterize initial growth dynamics before host defences have significant effects on the infecting parasite population. Of the 328 patients' data available for analysis, 83 were excluded because they had received anti-malarial treatment during the first 7 days of the patent infection. Nonlinear mixed effects modelling was performed to estimate the parameters of interest; ‘parasite multiplication rate per 48 h’ (PMR), and length of the parasite life-cycle (periodicity). The parasitaemia versus time profiles showed great variability between patients. The mean population estimate of ‘PMR’ was approximately 8, and was highly dependent on the P. falciparum ‘strain’. PMR also varied significantly between patients with a 90% prediction interval varying from 5·5 to 12·3-fold. Both intrinsic parasite multiplication rate (an intrinsic virulence determinant), and host susceptibility and defence contribute to expansion of the parasite biomass and thus disease severity in falciparum malaria.

Complete mitochondrial genomes confirm the distinctiveness of the horse-dog and sheep-dog strains of Echinococcus granulosus.

Abstract: Unlike other members of the genus, Echinococcus granulosus is known to exhibit considerable levels of variation in biology, physiology and molecular genetics. Indeed, some of the taxa regarded as 'genotypes' within E. granulosus might be sufficiently distinct as to merit specific status. Here, complete mitochondrial genomes are presented of 2 genotypes of E. granulosus (G1-sheep-dog strain: G4-horse-dog strain) and of another taeniid cestode, Taenia crassiceps. These genomes are characterized and compared with those of Echinococcus multilocularis and Hymenolepis diminuta. Genomes of all the species are very similar in structure, length and base-composition. Pairwise comparisons of concatenated protein-coding genes indicate that the G1 and G4 genotypes of E. granulosus are almost as distant from each other as each is from a distinct species, E. multilocularis. Sequences for the variable genes atp6 and nad3 were obtained from additional genotypes of E. granulosus, from E. vogeli and E. oligarthrus. Again, pairwise comparisons showed the distinctiveness of the G1 and G4 genotypes. Phylogenetic analyses of concatenated atp6, nad1 (partial) and cox1 (partial) genes from E. multilocularis, E. vogeli, E. oligarthrus, 5 genotypes of E. granulosus, and using T. crassiceps as an outgroup, yielded the same results. We conclude that the sheep-dog and horse-dog strains of E. granulosus should be regarded as distinct at the specific level.

Giardia lamblia disrupts tight junctional ZO-1 and increases permeability in non-transformed human small intestinal epithelial monolayers: effects of epidermal growth factor.

Abstract: In order to improve our understanding of the host cell-parasite interactions in giardiasis, this study assessed the effects of Giardia lamblia on epithelial permeability and tight junctional ZO-1, determined whether epidermal growth factor (EGF) may affect Giardia-induced epithelial injury, and evaluated if EGF modulates epithelial colonization by live G. lamblia trophozoites. Permeability was assessed in assays of trans-epithelial fluxes of FITC-dextran, and ZO-1 integrity was characterized by confocal laser immunofluorescence microscopy in confluent epithelial cell monolayers. G. lamblia significantly increased paracellular permeability and disrupted tight-junctional ZO-1 of a novel non-transformed human small intestinal epithelial cell line (SCBN). Pre-treatment with EGF prevented the development of these abnormalities and significantly inhibited attachment of live trophozoites to the enterocytes, independently of a direct microbiocidal action. These findings demonstrate that G. lamblia may cause intestinal pathophysiology by disrupting tight junctional ZO-1 and increasing epithelial permeability. Apical administration of EGF prevents these abnormalities, and reduces epithelial colonization by the live parasites.

Costs of resistance in insect-parasite and insect-parasitoid interactions.

Abstract: Most, if not all, organisms face attack by natural enemies and will be selected to evolve some form of defence. Resistance may have costs as well as its obvious benefits. These costs may be associated with actual defence or with the maintenance of the defensive machinery irrespective of whether a challenge occurs. In this paper, the evidence for costs of resistance in insect-parasite and insect-parasitoid systems is reviewed, with emphasis on two host-parasitoid systems, based on Drosophila melanogaster and pea aphids as hosts. Data from true insect-parasite systems mainly concern the costs of actual defence; evidence for the costs of standing defences is mostly circumstantial. In pea aphids, the costs of standing defences have so far proved elusive. Resistance amongst clones is not correlated with life-time fecundity, whether measured on good or poor quality plants. Successful defence by a D. melanogaster larva results in a reduction in adult size and fecundity and an increased susceptibility to pupal parasitoids. Costs of standing defences are a reduction in larval competitive ability though these costs only become important when food is limited. It is concluded that costs of resistance can play a pivotal role in the evolutionary and population dynamic interactions between hosts and their parasites.

The genetic control of IgA activity against Teladorsagia circumcincta and its association with parasite resistance in naturally infected sheep

Abstract: Previous studies in deliberately infected sheep have shown an association between IgA activity against 4th-stage larvae of Teladorsagia circumcincta and parasite growth, development and fecundity. The purpose of this research was to determine if these results could be confirmed in naturally infected sheep and to explore the hypothesis that plasma IgA activity could help to identify resistant lambs with shorter adult nematodes. Plasma IgA activity was skewed with most animals having relatively low levels of IgA activity. Plasma IgA activity was repeatable and highly heritable. Animals with increased IgA activity had lower egg counts and shorter adult female T. circumcincta. Therefore, under conditions of natural parasite challenge, plasma IgA activity may help to identify lambs resistant to T. circumcincta.

Mixed strain schistosome infections of snails and the evolution of parasite virulence

Abstract: Mathematical models often propose that within-host competition between parasites can be a major factor in the evolution of increased parasite virulence. Kin selection predicts that as the coefficient of relatedness between infecting parasites decreases, the benefits of competition to individual genotypes increases. Thus where parasites can adjust their behaviour in response to current conditions, higher virulence is predicted in multiple genotype infections. There is limited experimental data, however, regarding the effects of mixed strain infections on host and parasite fitness. We investigated, for a snail-schistosome system, whether a conditional increase in replication rates occurred in mixed genotype infections and resulted in increased virulence. Four groups of Biomphalaria glabrata snails were exposed to 1 or 2 laboratory strains of Schistosoma mansoni. Mixed genotype infections were observed to be more virulent than single genotype infections, in terms of reductions in host reproductive success and survival. Parasite reproductive rate was also increased in mixed strain groups. Reduced host reproductive success was suggested to be directly due to the genetic heterogeneity of the parasitic infections resulting in increased host defence costs. Reduced host survival was consistent with an adaptive conditional parasite response.

The trouble with sealworms (Pseudoterranova decipiens species complex, Nematoda): a review.

Abstract: Sealworms or codworms, larvae of ascaridoid nematodes belonging to the Pseudoterranova decipiens species complex, infect the flesh of numerous species of marine and euryhaline fish, and have proven a chronic and costly cosmetic problem for seafood processors. Moreover, the parasite may cause abdominal discomfort in humans when consumed in raw, undercooked or lightly marinated fish. In this review, the phylogeny, life cycle and distributions of sealworms are discussed along with biotic and abiotic factors which may influence distributions of these parasites in their intermediate and final hosts. Also considered here are efforts to control the problem through commercial fishing practices, fish processing technology, and the reduction of infection parameters in marine fish populations by biological means. Ironically, concern over sealworm problem has subsided in some fisheries in recent years, not as a result of falling infection parameters in fish stocks or innovations in processing technology, but as a consequence of declines in abundance and size of groundfish.

Needle in a haystack: involvement of the copepod Paracartia grani in the life-cycle of the oyster pathogen Marteilia refringens

Abstract: Marteilia refringens is a major pathogen of the European flat oyster, Ostrea edulis Linnaeus. Since its description, the life-cycle of this protozoan parasite has eluded discovery. Attempts to infect oysters experimentally have been unsuccessful and led to the hypothesis of a complex life-cycle involving several hosts. Knowledge of this life-cycle is of central importance in order to manage oyster disease. However, the exploration of M. refringens life-cycle has been previously limited by the detection tools available and the tremendous number of species to be screened in enzootic areas. In this study, these two restrictions were circumvented by the use of both molecular detection tools and a mesocosm with low biodiversity. Screening of the entire fauna of the pond for M. refringens DNA was systematically undertaken using PCR. Here, we show that the copepod Paracartia (Acartia) grani is a host of M. refringens. Not only was DNA of M. refringens consistently detected in P. grani but also the presence of the parasite in the ovarian tissues was demonstrated using in situ hybridization. Finally, successful experimental transmissions provided evidence that P. grani can be infected from infected flat oysters.

Triclabendazole-resistant Fasciola hepatica: β-tubulin and response to in vitro treatment with triclabendazole

Abstract: Resistance in Fasciola hepatica to triclabendazole ('Fasinex') has emerged in several countries Benzimidazole resistance in parasitic nematodes has been linked to a single amino acid substitution (phenylalanine to tyrosine) at position 200 on the beta-tubulin molecule Sequencing of beta-tubulin cDNAs from triclabendazole-susceptible and triclabendazole-resistant flukes revealed no amino acid differences between their respective primary amino acid sequences In order to investigate the mechanism of triclabendazole resistance, triclabendazole-susceptible and triclabendazole-resistant flukes were incubated in vitro with triclabendazole sulphoxide (50 microg/ml) Scanning and transmission electron microscopy revealed extensive damage to the tegument of triclabendazole-susceptible F hepatica, whereas triclabendazole-resistant flukes showed only localized and relatively minor disruption of the tegument covering the spines Immunocytochemical studies, using an anti-tubulin antibody, showed that tubulin organization was disrupted in the tegument of triclabendazole-susceptible flukes No such disruption was evident in triclabendazole-resistant F hepatica The significance of these findings is discussed with regard to the mechanism of triclabendazole resistance in F hepatica

SSCP-based identification of members within the Pseudoterranova decipiens complex (Nematoda: Ascaridoidea: Anisakidae) using genetic markers in the internal transcribed spacers of ribosomal DNA

Abstract: The anisakid nematodes morphologically corresponding with Pseudoterranova decipiens sensu lato (s.l.) (Krabbe, 1878) from different seal or sea lion hosts and geographical origins, previously identified as Pseudoterranova krabbei, P. decipiens (s.s.), P. bulbosa, P. azarasi and P. cattani by multilocus enzyme electrophoresis, were characterized using a DNA approach. Also a population of P. decipiens (s.l.) from Chaenocephalus aceratus, the blackfin icefish, from Antarctica and another from Osmerus eperlanus, the European smelt, from Germany were included in the study. The first (ITS-1) and second (ITS-2) internal transcribed spacers (ITS) of ribosomal DNA (rDNA) were amplified by PCR from individual nematodes and analysed by single-strand conformation polymorphism (SSCP), followed by selective sequencing. While no variation in single-stranded ITS-1 and ITS-2 profiles was detected among samples representing each of the species or populations (with the exception of slight microheterogeneity), SSCP analysis of the ITS-2 amplicons allowed the unequivocal differentiation of all of the 5 sibling species of P. decipiens (s.l.) examined, which was supported by sequence differences in ITS rDNA. Samples representing the P. decipiens (s.l.) population from O. eperlanus had the same SSCP profile as those of P. decipiens (s.s.), which was supported by a lack of nucleotide difference in the ITS between them, suggesting that the former represented P. decipiens (s.s.). Based on SSCP results and ITS sequence data, P. decipiens (s.l.) from C. aceratus was genetically most distinct with respect to all other members of Pseudoterranova examined, which indicated that it may represent P. decipiens E (based on geographical origin) or a distinct species. These findings and the molecular approach taken should have important implications for studying the life-cycles, transmission patterns, epidemiology and population genetics of these anisakid nematodes, and the diagnosis of their infections.

Properties, stage-dependent expression and localization of Plasmodium falciparum M1 family zinc-aminopeptidase.

Abstract: A Plasmodium falciparum single copy gene predicting a 122 kDa protein belonging to the M1 family of zinc-metallopeptidases was previously reported and related to erythrocytic schizont proteins of 96 (p96) and 68 (p68) kDa. By using protease inhibitors during parasite harvest and enzyme preparations, and polyclonal antibodies specific for 2 peptidic domains deduced from the gene, we identified the 120 kDa precursor and demonstrated its processing into p96 and p68. The N-terminal ends of p96 and p68 were mapped between glycine-123 and lysine-163, both proteins thus containing the catalytic domain. The purified enzyme, here named PfA-M1 (p96/p68), displayed strict aminopeptidase activity, optimal at pH 7·4, with broad substrate spectrum. Its inhibition and reactivation profiles were typical of zinc-metalloaminopeptidases. By Western blotting, PfA-M1 was detected in trophozoites, in addition to schizonts, but not in early rings. PfA-M1 was localized by indirect immunofluorescence confocal microscopy. In trophozoites, the labelling was diffuse in the parasite cytoplasm, with accumulations around the food vacuole. In schizonts, it turned progressively to a vesicle-like pattern, ending as a clear spot in released merozoites. The involvement of PfA-M1 in haemoglobin breakdown and erythrocyte reinvasion is discussed in light of the dual functions recently reported for several P. falciparum proteases.

Host immune responses are necessary for density dependence in nematode infections.

Abstract: Nematode infections are subject to density-dependent effects on their establishment, survivorship and fecundity within a host. These effects act to regulate and stabilize the size of nematode populations. Understanding how these density-dependent effects occur is important to guide the development of control strategies against parasitic nematodes and the diseases that they cause. These density-dependent effects have been hypothesized to result from intraspecific competition between parasites for limited resources or from the action of host immune responses. However, no specific evidence exists to distinguish between these two hypotheses. We find that in nematode (Strongyloides ratti) infections, density-dependent effects on parasite establishment, survivorship and fecundity are mediated by the host immune response. These density-dependent effects are only observed late in primary infections and no density-dependent effects are observed in infections in immuno-compromised animals. We find no evidence for intraspecific competition between parasites in experimental infections over a range of doses that encompasses all that is observed in natural infections. We conclude that density-dependent effects due to the immune response will act to regulate S. ratti infections before competition for space or nutrients within the host gut ever occurs.

Female mice mate preferentially with non-parasitized males.

Abstract: If parasitic infection is a driving force in female mate choice, then females should preferentially select parasite-free males. The role of infection on female mate choice in mammals was assessed using a 3-chambered apparatus. A female CD-1 mouse was allowed to choose between 2 tethered male mice, 1 uninfected and 1 infected with 200 larvae (L3) of the intestinal nematode Heligmosomoides polygyrus. Both uninfected and infected males were equally receptive to the oestrous females, and females did not differ in the number of visits and time spent exploring the 2 males. Female time preference was not a useful predictor of ultimate mate choice, whereas first mount preference of the female was a reliable indicator. Results indicate that female mice preferentially mated with uninfected males as evidenced by first ejaculation choice, but that male infection status did not significantly affect female reproductive success. Interestingly, litters sired by infected males contained a significantly higher percentage of females suggesting that parasite-induced hormonal changes may alter the sex ratio of the offspring. This study provides the first direct evidence of the impact of parasitic infection on mammalian mate choice.

Description of Enteromyxum scophthalmi gen. nov., sp. nov. (Myxozoa), an intestinal parasite of turbot (Scophthalmus maximus L.) using morphological and ribosomal RNA sequence data.

Abstract: A new Myxozoa species causing enteritis and death in cultured turbot, Scophthalmus maximus, is described at light and electron microscope levels. In addition, small subunit ribosomal RNA gene sequences (SSU rDNA) from the new species and from similar myxozoans were obtained and used for phylogenetic inference, as complementary criteria to resolve its taxonomic classification. The new parasite is closely related to Myxidium leei, another enteric histozoic species from marine fish. However, the ascription of M. leei to the genus Myxidium was based on weak morphological evidence and is not supported by our rDNA data analysis. A close relationship with Zschokkella, the other morphologically related myxozoan genus is also not supported. The combined morphological and molecular study results in the establishment of the new genus Enteromyxum to accommodate the new species E. scophthalmi, and the former M. leei, which is transferred to the new genus as Enteromyxum leei (Diamant, Lom & Dykova 1994) n. comb. This genus of marine, histozoic and enteric myxozoans includes significant parasite species for marine finfish culture.

An anti-atherogenic effect of Schistosoma mansoni infections in mice associated with a parasite-induced lowering of blood total cholesterol.

Abstract: In affluent societies the prevalences of so-called ‘Western’ diseases such as atherosclerosis, allergies and autoimmune disorders appear to have increased, while many diseases caused by communicable infections are now relatively less common. To test whether there may be a causal relationship we examined the effects of Schistosoma mansoni infections in mice that develop cardiovascular pathology as a result of a genetic deficiency in apolipoprotein E (apoE −/− ). The development of atherosclerotic lesions in the aortic arch and brachiocephalic artery of the apoE −/− mice was reduced by approximately 50% in mice with the parasitic infection, when comparison was made with uninfected control mice fed the same diet. Observations on S. mansoni -infected conventional laboratory mice indicate that patent schistosome infections could be counteracting the effects of an atherogenic diet by modulating host lipid metabolism and inducing a reduction in blood total cholesterol concentrations.

The persistence of Theileria parva infection in cattle immunized using two stocks which differ in their ability to induce a carrier state: analysis using a novel blood spot PCR assay

Abstract: An improved Theileria parva DNA detection assay based on the polymerase chain reaction (PCR) using primers derived from the 104 kDa antigen (p104) gene was developed to detect parasite DNA in blood spots on filter paper. The specificity of the assay was validated using DNA from a wide range of cattle-derived and buffalo-derived stocks of T. parva. DNA of T. annulata, T. buffeli, T. lestoquardi, T. mutans and T. taurotragi was not amplified using the p104 primers. The detection threshold of the assay was approximately 1-2 parasites/microl of infected blood. PCR amplification using the p104 primers was applied to sequential samples from groups of cattle experimentally infected with either the T. parva Marikebuni stock that induces a long-term carrier state or the Muguga stock, which does not induce a carrier state. The study extended for up to 487 days post-infection and PCR data from defined time points were compared with parasitological microscopy and serological data, together with xenodiagnosis by experimental application of ticks. Microscopy first detected piroplasms between days 13 and 16 after infection whereas all cattle became PCR +ve between days 9 and 13. Animals infected with the Muguga stock of T. parva had parasite DNA in the peripheral blood, which could be detected by PCR, for between 33 and 129 days post-infection in different animals. By contrast parasite DNA in the blood of cattle infected with the Marikebuni stock could be detected consistently from day 9 up to 487 days, when the study terminated. The data suggest that the nature and persistence of the carrier state may differ markedly between different T. parva parasite stocks.

Immune modulation by fish kinetoplastid parasites: a role for nitric oxide.

Abstract: Trypanoplasma borreli and Trypanosoma carassii are kinetoplastid parasites infecting cyprinid fish. We investigated the role of nitric oxide (NO) in immune modulation during T. borreli and T. carassii infection of carp. Phagocytic cells from different organs produced NO and serum nitrate levels increased, demonstrating that T. borreli activates NO production in vivo. In contrast, T. carassii did not induce NO production in vivo and inhibited LPS-induced NO production in vitro. Production of NO was detrimental to the host as T. borreli-infected carp treated with the inducible NO synthase inhibitor aminoguanidine had a higher survival than infected control carp. This detrimental effect can be explained (in part) by the toxicity of NO to cells in vitro as NO inhibited the proliferative response of blood and spleen leukocytes. Head-kidney phagocytes were resistant to the immunosuppressive effects of NO in vitro. The NO-inducing activity of T. borreli may be an adaptation developed to ensure survival and immune evasion in the fish host. Apparently, T. carassii has adopted another strategy by deactivating specific functions of phagocytes. Both strategies may ensure long-term survival of the parasite.

Low infectiousness of a wildlife host of Leishmania infantum: the crab-eating fox is not important for transmission.

Abstract: The epidemiological role of the crab-eating fox Cerdocyon thous in the transmission of Leishmania infantum is assessed in a longitudinal study in Amazon Brazil. A total of 37 wild-caught foxes were immunologically and clinically monitored, and 26 foxes exposed to laboratory colonies of the sandfly vector Lutzomyia longipalpis, over a 15-month period. In total 78% (29/37) of foxes were seropositive for anti-Leishmania IgG on at least 1 occasion, and 38% (8/37) had infections confirmed by PCR and/or by culture. Point prevalences were 74% (serology), 15% (PCR), and 26% (culture). No signs of progressive disease were observed. None of the foxes were infectious to the 1469 sandflies dissected from 44 feeds. A conservative estimate of the possible contribution of foxes to transmission was 9% compared to 91% by sympatric domestic dogs. These results show that crab-eating fox populations do not maintain a transmission cycle independently of domestic dogs. The implication is that they are unlikely to introduce the parasite into Leishmania-free dog populations.

Trypanosoma avium of raptors (Falconiformes): phylogeny and identification of vectors

Abstract: Avian trypanosomes are widespread parasites of birds, the transmission of which remains mostly unclear, with various blood-sucking insects mentioned as possible vectors. A search for vectors of trypanosomes of sparrowhawk (Accipiter nisus), buzzard (Buteo buteo), lesser-spotted eagle (Aquila pomarina) and kestrel (Falco tinnunculus) was performed in Czech and Slovak Republics. Black flies (Eusimulium spp.), hippoboscid flies (Ornithomyia avicularia), mosquitoes (Culex pipiens pipiens) and biting midges (Culicoides spp.), trapped while attempting to feed on raptor nestlings, were found to contain trypanosomatids in their intestine. Trypanosomes from the raptors and blood-sucking insects were isolated, and their 18S rRNA sequences were used for species identification and for the inference of intra- and interspecific relationships. Together with the trypanosome isolated from a black fly, the bird trypanosomes formed a well-supported Trypanosoma avium clade. The isolates derived from hippoboscid flies and mosquitoes are most likely also avian trypanosomes infecting birds other than the studied raptors. Analysis of the kinetoplast, that has features characteristic for the avian trypanosomes (minicircle size; dimensions of the kinetoplast disc), provided further evidence for the identification of vectors. It is suggested that all trypanosomes isolated from raptors included in this study belong to the T. avium complex and are transmitted by the ornithophilic simuliids such as Eusimulium securiforme.

Cleaning symbioses from the parasites' perspective.

Abstract: Cleaning behaviour has generally been viewed from the cleaner or client's point of view. Few studies, however, have examined cleaning behaviour from the parasites' perspective, yet they are the equally-important third players in such associations. All three players are likely to have had their evolution affected by the association. As cleaner organisms are important predators of parasites, cleaners are likely to have an important effect on their prey. Little, however, is known of how parasites are affected by cleaning associations and the strategies that parasites use in response to cleaners. I examine here what parasites are involved in cleaning interactions, the effect cleaners have on parasites, the potential counter-adaptations that parasites have evolved against the predatory activities of cleaner organisms, the potential influence of cleaners on the life history traits of parasites, and other factors affected by cleaners. I have found that a wide range of ectoparasites from diverse habitats have been reported to interact with a wide range of cleaner organisms. Some of the life history traits of parasites are consistent with the idea that they are in response to cleaner predation. It is clear, however, that although many cleaning systems exist their ecological role is largely unexplored. This has likely been hindered by our lack of information on the parasites involved in cleaning interactions.