Despite evidence for the existence of interspecific interactions between helminth species, there has been no theoretical exploration of their effect on the distribution of the parasite species in a host population. We use a deterministic model for the accumulation and loss of adult worms of 2 interacting helminth species to motivate an individual-based stochastic model. The mean worm burden and variance[ratio ]mean ratio (VMR) of each species, and the correlation between the two species are used to describe the distribution within different host age classes. We find that interspecific interactions can produce convex age-intensity profiles and will impact the level of aggregation (as measured by the VMR). In the absence of correlated exposure, the correlation in older age classes may be close to zero when either intra- or interspecific synergistic effects are strong. We therefore suggest examining the correlation between species in young hosts as a possible means of identifying interspecific interaction. The presence of correlation between the rates of exposure makes the interpretation of correlations between species more difficult. Finally we show that in the absence of interaction, strong positive correlations are generated by averaging across most age classes.

The major muscle systems of the metacercaria of the strigeid trematode, Apatemon cobitidis proterorhini have been examined using phalloidin as a site-specific probe for filamentous actin. Regional differences were evident in the organization of the body wall musculature of the forebody and hindbody, the former comprising outer circular, intermediate longitudinal and inner diagonal fibres, the latter having the inner diagonal fibres replaced with an extra layer of more widely spaced circular muscle. Three orientations of muscle fibres (equatorial, meridional, radial) were discernible in the oral sucker, acetabulum and paired lappets. Large longitudinal extensor and flexor muscles project into the hindbody where they connect to the body wall or end blindly. Innervation to the muscle systems of Apatemon was examined by immunocytochemistry, using antibodies to known myoactive substances: the flatworm FMRFamide-related neuropeptide (FaRP), GYIRFamide, and the biogenic amine, 5-hydroxytryptamine (5-HT). Strong immunostaining for both peptidergic and serotoninergic components was found in the central nervous system and confocal microscopic mapping of the distribution of these neuroactive substances revealed they occupied separate neuronal pathways. In the peripheral nervous system, GYIRFamide-immunoreactivity was extensive and, in particular, associated with the innervation of all attachment structures; serotoninergic fibres, on the other hand, were localized to the oral sucker and pharynx and to regions along the anterior margins of the forebody.

A major goal of community ecology is to identify and explain non-random patterns of species composition. To date, the search for nested patterns in parasite component communities of the same fish host species has not been attempted, despite the fact that this higher hierarchical level is more relevant to nestedness analyses. The aims of this study are first, to determine the structure of component communities – considering ectoparasites and endoparasites separately – of a marine fish (Sebastes capensis) with an extended geographical distribution along the southeastern Pacific and, second, to explain these patterns by taking into account the extrinsic factors associated with the distribution of this host fish. From April to September 2003 and from April to August 2004, 537 fish were captured from different latitudes along the southeastern Pacific. The component communities of both ectoparasites and endoparasites of this fish host showed significant nested subset patterns. However, the type of nestedness pattern differed between ectoparasites and endoparasites. Ectoparasite component communities of S. capensis show higher species richness between latitude 30°S and 40°S, whereas endoparasite component communities show higher species richness between 40°S and 52°S. A nested pattern in ectoparasite component communities of S. capensis result from the gradual loss of some ectoparasites species southward and northward of the central part of their latitudinal distribution, which can be explained by the interaction of S. capensis with other host fish species from the central Chilean coast. Nestedness in endoparasite component communities of S. capensis is produced by the gains and losses of species toward the south of their latitudinal distribution, caused by changes in their prey-items (intermediate hosts) along their latitudinal distributional range.

Trypanosoma (Megatrypanum) theileri from cattle and trypanosomes of other artiodactyls form a clade of closely related species in analyses using ribosomal sequences. Analysis of polymorphic sequences of a larger number of trypanosomes from broader geographical origins is required to evaluate the clustering of isolates as suggested by previous studies. Here, we determined the sequences of the spliced leader (SL) genes of 21 isolates from cattle and 2 from water buffalo from distant regions of Brazil. Analysis of SL gene repeats revealed that the 5S rRNA gene is inserted within the intergenic region. Phylogeographical patterns inferred using SL sequences showed at least 5 major genotypes of T. theileri distributed in 2 strongly divergent lineages. Lineage TthI comprises genotypes IA and IB from buffalo and cattle, respectively, from the Southeast and Central regions, whereas genotype IC is restricted to cattle from the Southern region. Lineage TthII includes cattle genotypes IIA, which is restricted to the North and Northeast, and IIB, found in the Centre, West, North and Northeast. PCR-RFLP of SL genes revealed valuable markers for genotyping T. theileri. The results of this study emphasize the genetic complexity and corroborate the geographical structuring of T. theileri genotypes found in cattle.

Glycosomes are specialized peroxisomes found in all kinetoplastid organisms. The organelles are unique in harbouring most enzymes of the glycolytic pathway. Matrix proteins, synthesized in the cytosol, cofactors and metabolites have to be transported across the membrane. Recent research on Trypanosoma brucei has provided insight into how these translocations across the membrane occur, although many details remain to be elucidated. Proteins are imported by a cascade of reactions performed by specialized proteins, called peroxins, in which a cytosolic receptor with bound matrix protein inserts itself in the membrane to deliver its cargo into the organelle and is subsequently retrieved from the glycosome to perform further rounds of import. Bulky solutes, such as cofactors and acyl-CoAs, seem to be translocated by specific transporter molecules, whereas smaller solutes such as glycolytic intermediates probably cross the membrane through pore-forming channels. The presence of such channels is in apparent contradiction with previous results that suggested a low permeability of the glycosomal membrane. We propose 3 possible, not mutually exclusive, solutions for this paradox. Glycosomal glycolytic enzymes have been validated as drug targets against trypanosomatid-borne diseases. We discuss the possible implications of the new data for the design of drugs to be delivered into glycosomes.

On parasitization with larval Brugia pahangi the infected flight muscle fibres of ‘resistant’ Anopheles labranchiae atroparvus undergo the following ultrastructural changes. The fibres become almost totally devoid of glycogen, their sarcoplasmic reticulum becomes elongate and closely associated with muscle fibrils. These fibrils degenerate and vesicles appear both within the degenerate fibril and within elements of the sarcoplasmic reticulum. Vesicles accumulate around the worm and degenerate to a uniform mass which eventually becomes melanized from its inner edge (next to the parasite) outwards.

The infected flight muscle fibres of both ‘resistant’ Aedes aegypti and ‘susceptible’ Aedes togoi are almost totally devoid of glycogen granules, but show no other ultrastructural change from the uninfected state.

Host-parasite interactions are shaped by the co-evolutionary arms race of parasite virulence, transmission success as well as host resistance and recovery. The virulence and fitness of parasites may depend on host condition, which is mediated, for instance, by host energy constraints. Here, we investigated to what extent stress imposed by predation threat and environmental pollutants influences host-parasite interactions. We challenged the crustacean host Daphnia magna with the sterilizing bacterial endoparasite Pasteuria ramosa and simultaneously exposed the host to fish kairomones, the pesticide carbaryl or both stressors. While parasite virulence, measured as impact on host mortality and sterilization, increased markedly after short-term pesticide exposure, it was not influenced by predation threat. Parasite fitness, measured in terms of produced transmission stages, decreased both in fish and pesticide treatments. This effect was much stronger under predation threat than carbaryl exposure, and was attributable to reduced somatic growth of the host, presumably resulting in fewer resources for parasite development. While the indirect impact of both stressors on spore loads provides evidence for host condition-dependent parasite fitness, the finding of increased virulence only under carbaryl exposure indicates a stronger physiological impact of the neurotoxic chemical compared with the effect of a non-toxic fish kairomone.

As genomic research continues to improve our understanding of the genetics of anthelmintic drug resistance, the revolution in DNA sequencing technologies will provide increasing opportunities for large-scale surveillance for the emergence of drug resistance. In most countries, parasite control in cattle and bison has mainly depended on pour-on macrocyclic lactone formulations resulting in widespread ivermectin resistance. Consequently, there is an increased interest in using benzimidazole drugs which have been used comparatively little in cattle and bison in recent years. This situation, together with our understanding of benzimidazole resistance genetics, provides a practical opportunity to use deep-amplicon sequencing to assess the risk of drug resistance emergence. In this paper, we use deep-amplicon sequencing to scan for those mutations in the isotype-1 β-tubulin gene previously associated with benzimidazole resistance in many trichostrongylid nematode species. We found that several of these mutations occur at low frequency in many cattle and bison parasite populations in North America, suggesting increased use of benzimidazole drugs in cattle has the potential to result in widespread emergence of resistance in multiple parasite species. This work illustrates a post-genomic approach to large-scale surveillance of early emergence of anthelmintic resistance in the field.

Sheep infected with Oesophagostomum columbianum showed anorexia, loss of weight, diarrhoea and macroscopically obvious oedema and inflammation of the alimentary tract. Arthus-like lesions caused by the larvae developed particularly in the large intestine.

The gross immunological responses of the sheep were associated with antibodies in greater titre within the mucus of the gut than in the serum. Acquired immunity was manifest through an antibody-antigen reaction which was localized mostly in the large intestine and which involved proliferation of the lymphoid tissue of the gut and an increased synthesis of protein. Lower titres of antibody in serum than in mucus may indicate leakage of antibody away from the gut. The direct effects of antibody were established by the respiratory inhibition of the 3rd-stage larvae. The presence of antibody was associated with particularly high concentrations of β globulin after first and β and γ globulins after second infection. Specific antibody was demonstrated in these protein fractions by blockage of electrophoretic movement by larval antigen in the buffer.

The antibody-antigen reaction may act as a trigger which releases the nonspecific effects of excess mucus production and oedema which causes mechanical dislodgement of the infection. The natural and specific respiratory inhibitory effects of mucus on the worm would facilitate this dislodgement process.

The greatest cellular reactions occurred where there was an active infection. Usually these reactions were associated with oedema, hyperaemia and an increase in the size of the mesenteric lymph nodes.

The caecal mucosa of wild young and adult grouse infected naturally with Trichostrongylus tenuis was examined by means of scanning electron microscopy and compared with adult grouse which had been treated with an anthelmintic. The caecal mucosa of young red grouse with low worm burdens possessed longitudinal plicae and exhibited little damage. The caeca from adult grouse, most of which carried high worm burdens, showed a localized depression of plicae and atrophy and cell disruption in areas of nematode aggregation. Caeca from adult birds treated with an anthelmintic showed a similar caecal structure to lightly infected caeca from young birds. It is concluded that the normal functioning of the caeca is probably affected by heavy infections of T. tenuis.

The structure of the sporozoite of Eimeria tenella has been studied with the aid of the electron microscope, using both sectioned fixed material and negatively stained or shadowed whole cells. An apical ring gives rise to a series of 24 fibrils which extend posteriorly under a double bilamellar membrane. Within the apical ring lies a conoid with spirally arranged tubules and an apical pore; under some conditions at least this conoid can be pushed forward beyond the apical ring. Originating within the conoid are a group of club-shaped organelles which extend backwards into the cell to lie among an extensive regular array of micronemes. The nucleus lies between two apparently structureless paranuclear bodies, and scattered throughout the remaining cytoplasm are mitochondria with tubular cristae, oval structures containing amylopectin, occasional lipid droplets, and vesicles containing nondescript material possibly undergoing digestion and which may have a possible connexion with a lateral micropyle.

I am indebted to Mrs Muriel Bentley for much technical collaboration and to Mrs McLaren for making her manuscript available before publication.

The fine structure of the macrogametocyte, macrogamete and the early stages in the formation of the oocyst wall of Eimeria acervulina have been described and compared with other species of Eimeria. It has been shown that type II wall-forming bodies are formed in cisternae of the granular endoplasmic reticulum in association with Golgi complexes. The developing oocyst has been shown to be enclosed by three membranes: the outermost is the original membrane of the merozoite and macrogametocyte; the second membrane appears when the wall-forming bodies are appearing in the cytoplasm of the macrogametocyte and the innermost membrane appears after fertilization. The wall-forming bodies discharge their contents between the innermost membrane and the middle membrane.

We wish to thank Mr P. L. Long for much valuable discussion, Mrs B. Fisher for technical assistance and Mr B. Carter for assistance with the photography.

The relationship between infection rates of rainbow trout (Salmo gairdneri) by Diplostomum spathaceum and cercarial concentration, water flow rate and temperature were investigated by means of controlled infections within a flume. A linear relationship was obtained between cercarial concentration and mean abundance of metacercariae/fish. A biphasic relationship occurred between flow rate and abundance of metacercariae. Within the confines of the flume, it was possible to control the infection rate of trout with D. spathaceum cercariae by manipulating flow rate, suggesting that it may be a possible method of controlling diplostomiasis on fish farms. No infection occurred in fish infected and maintained below 10°C and the optimum infection temperature was approximately 17·5°C. Infections became established in fish infected at 7·5 and 5°C but maintained at 15°C prior to examination. Trout were infected at 7·5°C for 10–50 min and all attached cercariae were washed off and removed from the flume. Following infection, fish were either maintained at 7·5°C or 15°C prior to examination. Using this method, it was possible to ascertain that it was migration and not penetration which was inhibited at water temperatures below 10°C.

Leishmania parasites are able to survive in host macrophages despite the harsh phagolysosomal vacuoles conditions. This could reflect, in part, their capacity to secrete proteins that may play an essential role in the establishment of infection and serve as targets for cellular immune responses. To characterize Leishmania major proteins excreted/secreted early after promastigote entry into the host macrophage, we have generated antibodies against culture supernatants of stationary-phase promastigotes collected 6 h after incubation in conditions that partially reproduce those prevailing in the parasitophorous vacuole. The screening of an L. major cDNA library with these antibodies led us to isolate 33 different cDNA clones that we report here. Sequence analysis revealed that the corresponding proteins could be classified in 3 groups: 9 proteins have been previously described as excreted/secreted in Leishmania and/or other species; 11 correspond to known proteins already characterized in Leishmania and/or other species although it is unknown whether they are excreted/secreted and 13 code for unknown proteins. Interestingly, the latter are transcribed as shown by RT-PCR and some of them are stage regulated. The L. major excreted/secreted proteins may constitute putative virulence factors, vaccine candidates and/or new drug targets.

Much of what is currently known of the host-parasite interaction between mice and the parasitic nematode Trichuris muris has come from experiments using a single parasite isolate (E/N). This isolate has been compared with 2 others which, on morphological criteria, belong to the same species. In 3 inbred strains of mouse that show distinct, genetically determined response phenotypes, there was a consistent pattern in terms of parasite survival time regardless of host strain, E/K worms being expelled early, E/N expelled later and S worms very late or not at all. High-responder CBA mice expelled E/K and E/N worms earlier than low-responder C57 B1/10 mice. B10.BR mice were permissive to S isolate infection, mounted a very late response to E/N worms but expelled E/K worms effectively by day 25. The differential response of mice to these isolates provides an experimental system for identifying the basis of variation in this host-parasite relationship.

The sexual life-history traits of Schistosoma mansoni have been reviewed to compare male and female performance and pathogenicity against Biomphalaria glabrata during the life-cycle. A meta-analysis was used on pooled results from different experiments. In most cases, there was no difference between males and females but male cercariae were significantly more infectious than female cercariae. Conversely, cercarial production and cercarial life-span were significantly greater for females than for males; furthermore, females have a tendency to occur in molluscs of larger size. Each difference is discussed and interpreted when possible in terms of male and female differences in transmission strategies. The female strategy may consist of producing many long-living larvae. The male strategy may consist of producing few short-living larvae and would invest in the quality of these larvae instead of their quantity or their life-span.

This work reports a new type of actinospore, Unicapsulactinomyxon, which exhibits a unique morphological characteristic in that it has a single and large polar capsule (9·3×4·1 μm) (which possesses a longitudinally-folded polar filament) instead of the 3 polar capsules previously described for actinosporeans. The spore has a binucleated sporoplasm and 3 valves, each of which forms a long process. The spore has a total length of 241·3 μm. This parasite develops in groups of 8 inside pansporocysts in the coelomic cavity of the polychaete host. Molecular investigations on the SSU rDNA show that the new actinospore type is most closely related to Enteromyxum species (81–84% similarity). A survey of actinospore infections of the marine polychaete Diopatra neapolitana in 2007 and 2009, in the Aveiro Estuary (Portugal), showed an annual prevalence of 1·0% and 0·3%, respectively.

A thorough study of parasitic helminth antigens is a pre-requisite for control programmes based on accurate immunochemical diagnosis, protection by vaccination and perhaps immune modulation to diminish pathological sequelae. Studies should be directed at the identification of those stage- or age-specific surface, secreted and somatic antigens which are involved in the host-parasite interactions responsible for immunity and/or pathology. Current methods of diagnosis of parasitic infections often fail to detect low-level patent infections, which incurs the risk of having a reservoir capable of perpetuating infections. There is, then, an urgent requirement for accurate immunochemical diagnosis, to be used in association with, and for the evaluation of, drug treatment and vector elimination, in parasite control programmes. Given the high sensitivity of current immunoassay technology, the only bar to establishing the necessary immunological tests is the choice of suitably specific antigen/antibody systems. Assays designed to detect parasite products or antigens are a major priority, as they indicate current infection, whereas those which detect antibody only indicate exposure to infection, which may or may not be current. Surface and secreted antigens are the most likely targets for protective immune responses and thus form a logical focus for vaccine design. The cestodes, which present such strong evidence for immunity following natural infection, are likely to yield effective vaccines by modern procedures. Certain antigens must, however, stimulate the humoral and/or cellular responses which are responsible for the undesirable immunopathological consequences of many helminthic diseases. The nematodes and trematodes furnish some extreme examples of such pathology. The ultimate objective in identifying these particular antigens is to utilize them in the appropriate down-regulation of the immune response responsible for such pathology. As an illustration, we have presented an interesting correlation between one particular clinical condition of onchocerciasis (Sowda) and the serological response, defined both in terms of the parasite antigens and an immunoglobulin class-restricted antibody response. Finally, the complexity of these parasite systems and the host response to the parasite should not be underestimated. Modern analytical techniques allow their detailed analysis in terms of the humoral antibody responses and afford the possibility of the future development of control and disease management procedures tailored to each individual host-parasite system. However, novel systems are required to complete the analysis of the cellular components of the immune response to parasite antigens, and functional studies are needed to determine the role that these parasite antigens play in the complex interaction between parasite and host.

The ookinete is one of the most important stages of Plasmodium development in the mosquito. It is morphologically and biochemically distinct from the earlier sexual stages - gametocytes and zygote, and from the later stages - oocyst and sporozoites. Development to ookinete allows the parasite to escape from the tightly packed blood bolus, to cross the sturdy peritrophic matrix (PM), to be protected from the digestive environment of the midgut lumen, and to invade the gut epithelium. The success of each of these activities may depend on the degree of the biochemical and physical barriers in the mosquito (such as density of blood bolus, thickness of peritrophic matrix, proteolytic activities in the gut lumen etc.) and the ability of the ookinete to overcome these barriers. Ookinete motility, secretion of chitinase, resistance to the digestive enzymes, and recognition/invasion of the midgut epithelium all may play crucial roles in the transformation to oocyst. The overall sporogonic development of Plasmodium, therefore, depends on the results of the two-way manipulations between the parasite and the vector mosquito. Study of ookinete development and of the cellular and biochemical complexities of the mosquito gut may therefore lead to the design of novel strategies to block the transmission of malaria. This article reviews the intricate interactions between the parasite and the mosquito midgut in the context of development and transmission of Plasmodium parasites.