The prevalence and abundance of infections with haemoparasites were studied over a 3 year period in Clethrionomys glareolus (bank vole, n=420) sampled from forests in the NE of Poland. Total species richness was 5 (Prevalence=Haemobartonella sp. 63·1%, Bartonella grahamii 27·4%, Hepatozoon erhardovae 31·4%, Trypanosoma evotomys 15% and Babesia microti 1·0%) with 81·9% of the voles carrying at least 1 species and a mean infracommunity species richness of 1·4. Variation in species richness was determined primarily by season and year, and the interaction of these factors. The observed frequency distribution of infracommunity species richness did not differ from that predicted by a null model, suggesting that there were no marked associations between the species. Analyses of prevalence and abundance of infection with each species in turn, revealed that overall the principal causes of variation were temporal and seasonal and their interaction, intrinsic factors such as age and sex playing only a minor role. However, the relative importance of specific extrinsic, and rarely intrinsic, factors varied and was distinct for each of the species in the study. Prevalence data revealed 4 sets of 2-way associations between species, mostly varyingly dependent on combinations of intrinsic and extrinsic factors. Analysis of quantitative associations suggested 4 sets of positive 2-way interactions, 3 of which remained after controlling for the effect of extrinsic and intrinsic factors on the abundance of each species, but only one could be unequivocally accepted (Haemobartonella sp.+B. grahamii) after correction for multiple comparisons. These data are discussed in the context of the changing ecological profiles in this region of Eastern Europe and, in a wider context, in relation to current understanding of the factors which shape component community structures of haemoparasites in wild rodents.

We studied infection dynamics of Plasmodium chabaudi in mice infected with 3 genetically distinct clones – 1 less virulent than the other 2 – either on their own or in mixtures. During the acute phase of infection, total numbers of asexual parasites in mixed-clone infections were equal to those produced by the 3 clones alone, suggesting strong in-host competition among clones. During the chronic phase of the infection, mixed-clone infections produced more asexual parasites than single-clone infections, suggesting lower levels of competition than during the acute phase, and indicating that a genetically diverse infection is harder to control by the host immune system. Transmission potential over the whole course of infection was lower from mixed-clone infections than from the average of the 3 single-clone infections. These results suggest that in-host competition reduces both growth rate and probability of transmission for individual parasite clones.

Within each of the four species groups of Bulinus there are species that act as intermediate hosts for one or more of the seven species of schistosomes in the Schistosoma haematobium group, which includes the important human pathogens S. haematobium and S. intercalatum. Bulinus species have an extensive distribution throughout much of Africa and some surrounding islands including Madagascar, parts of the Middle East and the Mediterranean region. Considerable variation in intermediate host specificity can be found and differences in compatibility between snail and parasite can be observed over small geographical areas. Molecular studies for detection of genetic variation and the discrimination of Bulinus species are reviewed and two novel assays, allele-specific amplification (ASA) and SNaPshot™, are introduced and shown to be of value for detecting nucleotide changes in characterized genes such as cytochrome oxidase 1. The value and complexity of compatibility studies is illustrated by case studies of S. haematobium transmission. In Senegal, where B. globosus, B. umbilicatus, B. truncatus and B. senegalensis may act as intermediate hosts, distinct differences have been observed in the infectivity of different isolates of S. haematobium. In Zanzibar, molecular characterization studies to discriminate between B. globosus and B. nasutus have been essential to elucidate the roles of snails in transmission. B. globosus is an intermediate host on Unguja and Pemba. Further studies are required to establish the intermediate hosts in the coastal areas of East Africa. Biological factors central to the transmission of schistosomes, including cercarial emergence rhythms and interactions with other parasites and abiotic factors including temperature, rainfall, water velocity, desiccation and salinity are shown to impact on the intermediate host-parasite relationship.

The taxonomic and phylogenetic relationships of Trypanosoma vivax are controversial. It is generally suggested that South American, and East and West African isolates could be classified as subspecies or species allied to T. vivax. This is the first phylogenetic study to compare South American isolates (Brazil and Venezuela) with West/East African T. vivax isolates. Phylogeny using ribosomal sequences positioned all T. vivax isolates tightly together on the periphery of the clade containing all Salivarian trypanosomes. The same branching of isolates within T. vivax clade was observed in all inferred phylogenies using different data sets of sequences (SSU, SSU plus 5.8S or whole ITS rDNA). T. vivax from Brazil, Venezuela and West Africa (Nigeria) were closely related corroborating the West African origin of South American T. vivax, whereas a large genetic distance separated these isolates from the East African isolate (Kenya) analysed. Brazilian isolates from cattle asymptomatic or showing distinct pathology were highly homogeneous. This study did not disclose significant polymorphism to separate West African and South American isolates into different species/subspecies and indicate that the complexity of T. vivax in Africa and of the whole subgenus Trypanosoma (Duttonella) might be higher than previously believed.

Experiments were designed to look at the relationship between infective dose and disease severity using 2 clones of Plasmodium chabaudi that differ in virulence. We asked whether there were dose–severity relationships, whether clone differences in virulence were maintained over a range of doses, and whether disease severity could be accounted for by parasite dynamics. Groups of mice were infected with parasite doses differing by an order of magnitude, ranging from 100 to 1×108 parasites. Infective dose affected the probability of death, but only with the more virulent clone. Dose also affected morbidity. For both clones, higher doses induced greater anaemia. Larger doses caused greater weight loss, but only for infections with the more virulent clone. Here, for a given dose, mice lost a fixed amount of weight, irrespective of their initial weight. Larger doses induced earlier mortality and morbidity than did lower dose treatments. Finally, dose affected parasite dynamics, with earlier and higher peak parasite densities in larger dose infections. All these effects were small relative to clone differences in disease severity, which were apparent across the range of doses. Dose effects were manifested through the timing and/or magnitude of peak parasite densities, broadly supporting the idea that dose affects disease severity by altering the time the host has to control parasite densities and ameliorate the effects of parasites. We discuss the possible efficacy of intervention strategies aimed at reducing human disease severity by reducing infective parasite dose.

The observation that the total abundance of adult nematodes in the abomasum of Svalbard reindeer increases between October and April suggests adaptation to cope with the Arctic winter. Here we investigate the extent to which selection has led to similar life-history strategies in the 3 most numerous trichostrongyle species. The life-histories are found to differ markedly. We use flexible statistical models for the abundance and dispersion of parasites in the host population. One of the taxa, Marshallagia marshalli, was most abundant and had its highest egg output in the winter. In contrast, the abundance of the most common taxa, Ostertagia gruehneri, m. gruehneri was stable or declined from autumn to late winter, and the closely related taxa, O. gruehneri, m. arcticus, showed a similar over winter drop. The faecal egg output of these 2 taxa was highest in summer, as found in temperate trichostrongyle species. Despite the apparent contamination of summer pastures with O. gruehneri, calves showed negligible burdens until their second summer and the abundance of infection reached an asymptote within their third year. In contrast, the abundance of M. marshalli in calves showed a rapid increase over the first summer and by late winter was similar to peak levels found in adults (8000 worms). This increase could not be accounted for by the developing abomasum larvae population and is therefore evidence for transmission over the winter for this taxa. While M. marshalli showed little between-year variation, O. gruehneri showed 2-fold fluctuation in the abundance of infection. O. gruehneri may therefore play a role in the fluctuating population dynamics of the host. Since there was no apparent decline in abundance with host age in any of the 3 taxa there was no evidence of reindeer mounting an immune response.

Taenia crassiceps is a cestode parasite of wild and domestic animals that rarely affects humans; it has been widely used as an experimental model. The asexual proliferation by budding is a useful attribute of T. crassiceps cysticerci, which allows the various strains to be maintained indefinitely in the peritoneal cavity of inbred mice. Over the last 50 years, experimental results using larval and adult stages of T. crassiceps have yielded much information on the morphology, infectivity, proliferation dynamics, host immune response, endrocrinological responses and vaccine research, all of which have contributed to our knowledge of cestode biology.

The reproduction of Eimeria vermiformis in different strains of phenotypically normal mice and in mice with various immunological characteristics or defects was compared. In some strains of phenotypically normal mice there were marked differences in oocyst production, both in terms of numbers and in the duration of patency, allowing the strains to be classified as resistant or susceptible to infection with E. vermiformis. These differences were apparent only in primary infections; both types of strain were equally resistant to reinfection. Amongst the strains of mice with immunological deficiencies, reproduction of the parasite was greatest in the athymic (nu/nu) mutants and these mice were completely susceptible to reinfection. Strains of mice with lowered or defective antibody production, or with defective neutrophils and low NK cell activity (bg/bg) were more susceptible than the relevant controls to primary infection but all developed substantial immunity to reinfection. Asplenic (Dh/+) mutants were remarkably resistant to infection.

Angiostrongylus vasorum is a nematode parasite of sylvan and domestic species of the family Canidae. It has a broad but patchy distribution worldwide, and there is evidence for geographical spread and increasing incidence of infection in recent years. While historically Angiostrongylus-like nematodes identified in dogs and foxes have been described as A. vasorum in Europe and Angiocaulus raillieti in South America, more recent taxonomic revision has amalgamated these into a single species, A. vasorum. Here we report, for the first time, the molecular characterization of isolates of A. vasorum from Germany, Portugal, Denmark and the United Kingdom on the basis of the mitochondrial COI gene and the second ribosomal internal transcribed spacer. When compared with isolates from Brazil, sequence analysis revealed 2 distinct genotypes. Estimated rates of evolution based on COI sequences for both nematode and host are consistent with the hypothesis that the presence of A. vasorum in South America is a result of an ancient evolutionary event. Angiostrongylus vasorum in South America potentially represents a separate species to that observed in Europe.

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.

Phylogenetic analyses based on the partial large subunit rDNA (LSU) sequences of polyonchoinean monogeneans belonging to the Dactylogyridea and Monocotylidea were generated to investigate relationships among various subfamilies of the Dactylogyridae sensu Kritsky & Boeger, 1989. Monophyly of the Dactylogyridae was supported by all analyses performed. Status of the Ancyrocephalidae sensu Bychowsky & Nagibina, 1978 and Ancyrocephalinae sensu Kritsky & Boeger, 1989 was revised based on the present data. All phylogenetic analyses indicated polyphyletic origins of the Ancyrocephalidae and Ancyrocephalinae. Freshwater species of Ancyrocephalinae (Actinocleidus, Ancyrocephalus, Cleidodiscus and Urocleidus) and Ancylodiscoidinae (Thaparocleidus) collected from the fish in European waters were positioned at the base of the Dactylogyridae. The Dactylogyrinae formed a monophyletic group, sister to a clade including the Pseudodactylogyrinae and the tropical and subtropical Ancyrocephalinae. Analyses including only data set on Dactylogyridea were focused on relationships between representatives of the Asian and European Dactylogyrus species. Dactylogyrus species formed a monophyletic group, and the parasite colonization appeared to follow the dispersal history of the Cyprinidae from Asia to Europe. Three lineages of Dactylogyrus species were recognized: the first including species specific to hosts of Asian origin, the second by Dactylogyrus species from Chinese fish hosts, and the third included Dactylogyrus species from European cyprinids and one species from a percid host. The position of D. cryptomeres from Gobio gobio seems to be unresolved.

Reinfection with hookworm (Necator americanus) following chemotherapy was studied over 2 years in a rural village in Madang Province, Papua New Guinea. The prevalence of hookworm infection had returned to pre-treatment levels after 2 years, and the geometric mean hookworm burden had returned to 58 % of the pre-treatment value. The rate of acquisition of adult worms was independent of host age, and was estimated as a geometric mean of 2·9–3·3 worms/host/year (arithmetic mean 7·9–8·9 worms/host/year). There was significant predisposition to hookworm infection; the strength of this predisposition did not vary significantly between age or sex classes.

An analysis of the rostellar hooks of Australian isolates of Echinococcus granulosus revealed that there was less variation in larval (metacestode) than adult characters and that metacestode characters could be measured directly from adult worms. A factor analysis indicated that two factors, one representing a contrast between number of hooks and their length, and the other representing blade lengths, were sufficient to account for 87.5% of the variance in metacestode hook measurements. These results indicate that rostellar hook morphology is not useful for discriminating strains of E. granulosus in Australia. The Tasmanian and mainland domestic strains were found to be indistinguishable using rostellar morphology. Although many of the isolates from sylvatic hosts differed from those from domestic hosts, there was not a clear separation as would be expected if two distinct strains existed. Evidence was presented to show that the morphological differences seen in sylvatic hosts could be attributed to host-induced effects, and that the previously accepted existence of two mainland strains should be investigated further.

Mice were infected per os with Trichinella spiralis and their lymphocytes were removed and fused with mouse myeloma cell line P3 × 63Ag8653P3 for the selection of monoclonal antibodies to biochemically defined, stage-specific surface antigens of 3 parasite developmental stages: muscle larvae, adults and newborn larvae. Two separate antibodies against a defined single surface antigen of each stage were isolated. In each separate case the pair of monoclonal antibodies precipitated the same component from detergent-solubilized surface antigen preparations, but only one was able to bind to the surface of the living worm. The other must therefore be directed against an antigenic epitope which is obscured in the intact worm surface. The latter type of antibody is unlikely to be involved in the initial phase of parasite rejection and hence is another example of a non-protective host antibody response. The stimulus for its synthesis may be release of surface antigen, which does occur in vitro. One surface antigen of the newborn larvae is only detected by antibody in the first 6 h after birth; thereafter its presence is obscured as other antigens appear. The major surface antigen of the infective larvae contains carbohydrate determinants which are not available at the parasite surface. In addition, it displays great molecular heterogeneity but all variants appear to be derived from a common polypeptide structure.

Plant-parasitic nematodes cause considerable damage to global agriculture. The ability to parasitize plants is a derived character that appears to have independently emerged several times in the phylum Nematoda. Morphological convergence to feeding style has been observed, but whether this is emergent from molecular convergence is less obvious. To address this, we assess whether genomic signatures can be associated with plant parasitism by nematodes. In this review, we report genomic features and characteristics that appear to be common in plant-parasitic nematodes while absent or rare in animal parasites, predators or free-living species. Candidate horizontal acquisitions of parasitism genes have systematically been found in all plant-parasitic species investigated at the sequence level. Presence of peptides that mimic plant hormones also appears to be a trait of plant-parasitic species. Annotations of the few genomes of plant-parasitic nematodes available to date have revealed a set of apparently species-specific genes on every occasion. Effector genes, important for parasitism are frequently found among those species-specific genes, indicating poor overlap. Overall, nematodes appear to have developed convergent genomic solutions to adapt to plant parasitism.

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.

Most of the successful anti-nematode drugs currently available affect the nematode locomotory system. Their success is due to their interactions with molecules associated with the main neuro-transmitters of the motor nervous system, acetylcholine and GABA. These drugs tend to have a relatively broad spectrum of action, affecting a wide variety of nematodes, presumably because nematode motor nervous systems are conservative in their use of these transmitters.

The cyst wall which encloses the metacercaria of Fasciola hepatica consists of four major layers, one of which is further divisible into three sublayers. These layers are numbered I to IV, the first being the external layer. Layers I and II form the outer cyst which may be separated from the inner cyst formed from layers III and IV.

Layer I, the thick incomplete external layer, covers the metacercaria dorsally and laterally. It is composed of tanned protein.

Layer II is a thin fibrous layer closely adherent to the inner surface of layer I and is composed of mucoprotein and acid mucopolysaccharide.

Layer III is made up of three separate sublayers, the relative widths of which vary in different regions of the cyst. In general IIIa consists of mucoprotein, IIIb of acid mucopolysaccharide and IIIc of neutral mucopolysaccharide.

In the dorsal and lateral regions, layer IV appears to be formed of lamellae held in a protein–lipid matrix. The lamellae are composed of protein stabilized by disulphide linkages.

In the ventral region of layer IV there is a thickened mucopolysaccharide area, the ventral plug, through which the metacercaria excysts.

The relative importance of these resistant layers in providing protection against desiccation, toxic substances and attack by other organisms is discussed.

This work was carried out during the tenure of a Commonwealth Post Graduate Scholarship. The author is grateful to Professor J. D. Smyth and Dr J. A. Clegg for advice and encouragement during the course of this work and in preparation of the manuscript.

Incubation of adult Schistosoma mansoni at 37 °C in chemically defined media caused the shedding of variable amounts of the parasite's tegument. In phosphate-buffered saline, pH 7·4, 37% of 125I-labelled wheat germ agglutinin which was attached to the schistosome surface was released within 5 min. When the released material was collected by centrifugation at 55000 g for 1 h, the pellet was seen to consist of components of the parasite tegument and contained 1% of the parasite protein and 6·2% of the 5′-AMPase activity. By monitoring the release of the gut enzyme, haemoglobinase, it was shown that predominantly tegumental material was released under these conditions. The material released from the parasite was separated by discontinuous sucrose gradient centrifugation into 4 major fractions and it was shown that a material banding at low density was highly enriched in vesicles of parasite outer membrane. Major polypeptides of apparent molecular weights 135000, 110000, 90000, 65000, 47000 and 40000 and glycoproteins of apparent molecular weights 135000, 120000, 65000, 63000 and 30–40000 were identified in this fraction. Comparison of the distribution of 5′-AMPase activity and the contents of each fraction as revealed by ultrastructural examination showed that this enzyme is a good marker for the tegumental outer membrane.