Human fascioliasis is a worldwide, pathogenic food-borne trematodiasis. Impressive clinical pictures comprising puzzling polymorphisms, manifestation multifocality, disease evolution changes, sequelae and mortality, have been reported in patients presenting with neurological, meningeal, neuropsychic and ocular disorders caused at distance by flukes infecting the liver. Proteomic and mass spectrometry analyses of the Fasciola hepatica excretome/secretome identified numerous, several new, plasminogen-binding proteins enhancing plasmin generation. This may underlie blood-brain barrier leakage whether by many simultaneously migrating, small-sized juvenile flukes in the acute phase, or by breakage of encapsulating formations triggered by single worm tracks in the chronic phase. Blood-brain barrier leakages may subsequently occur due to a fibrinolytic system-dependent mechanism involving plasmin-dependent generation of the proinflammatory peptide bradykinin and activation of bradykinin B2 receptors, after different plasminogen-binding protein agglomeration waves. Interactions between diverse parasitic situations and non-imbalancing fibrinolysis system alterations are for the first time proposed that explain the complexity, heterogeneity and timely variations of neurological disorders. Additionally, inflammation and dilation of blood vessels may be due to contact system–dependent generation bradykinin. This baseline allows for search of indicators to detect neurological risk in fascioliasis patients and experimental work on antifibrinolytic treatments or B2 receptor antagonists for preventing blood-brain barrier leakage.

Widespread use of ivermectin (IVM) as part of the Onchocerciasis Control Program (OCP) in West Africa could influence the evolution of the human filarial parasite Onchocerca volvulus. Use of IVM, in some areas for 15 years, may have restricted genetic diversity of O. volvulus, resembling effects attributed to a population bottleneck. Large population-based chemotherapy programmes, such as the OCP, may impose strong selection pressure on parasites and an examination of possible genetic selection by IVM in O. volvulus is warranted. IVM is a substrate for P-glycoprotein; a homologue from O. volvulus (OvPGP) has been linked with IVM sensitivity. Linkage disequilibrium (LD) patterns of 28 genetic markers spanning the OvPGP locus were examined in 4 O. volvulus populations from the Volta Region of Ghana, West Africa. Reduced gene diversity, increased heterozygosity and an increase in the number of markers not in Hardy-Weinberg equilibrium were associated with increasing IVM treatment. The number of regions in LD decreased with treatment and with time. However, between 1999 and 2002, seven regions of OvPGP were always in complete LD, while surrounding areas showed a reduction in genetic variation. The use of IVM for onchocerciasis control has imposed strong selection on O. volvulus populations, reducing genetic variation and disrupting LD.

Faecal egg counts and peripheral blood eosinophil counts were taken from Scottish Blackface lambs following natural, predominantly Teladorsagia circumcincta infection. Peripheral eosinophil concentrations were higher in animals with lower egg counts but only in lambs that were at least 3 months of age. The reduced egg counts were due to reduced fecundity of T. circumcincta; there was no association with the number of adult T. circumcincta. Associations with the number of parasites from other species of gastrointestinal nematodes appeared to be neutral or favourable. Estimated heritabilities for eosinophil concentrations in 4- and 5-month-old lambs were 0·48±0·16 and 0·43±0·17, respectively. Therefore, under defined circumstances, eosinophil concentrations may be a useful indicator of resistance to predominantly T. circumcincta infection.

Detailed knowledge of the effects of water on the migration of infective larvae of economically important trichostrongyloid species is urgently needed to feed into prediction models of future epidemiology. The influence of water on the migration of the parasitic nematodes Nematodirus battus, Haemonchus contortus and Teladorsagia circumcincta from sheep dung onto grass was examined in a series of laboratory experiments. Turf plots were seeded with larvae, which were recovered from grass clippings by serial sampling. Free water was necessary for larvae to escape from dung, but not for vertical migration onto grass. When temperature and relative humidity were held constant, the proportion of a population of live larvae present on herbage reached a plateau of around 2 (1–10)% after 24 h, and then changed little over time. Larvae in soil and dung formed a reservoir, such that a similar proportion of the larval population was maintained on grass after clipping. These findings suggest continuing random movement of free larvae. Implications for the epidemiology of trichostrongyloid species are discussed in the context of trade-offs faced by the parasites.

The relationship between faecal nematode egg count and the number of adult Telordasagia circumcincta was examined in 508 naturally infected lambs at 6–7 months of age. The relationship was found to be convex and was empirically described by a gamma-type function of the form y = anb e−cn, where n is the number of adult nematodes present and y is the number of nematode eggs per gramme (epg) of faeces. This equation predicted that the peak expected egg count (277 epg) would occur at a worm burden of 2167 adult worms. The absence of a linear relationship between egg counts and worm numbers is consistent with the existence of severe density-dependent constraints on the fecundity of T. circumcincta.

Haemoflagellates of the genus Trypanosoma are prevalent in freshwater fishes and are transmitted by leeches as vectors. As demonstrated by sequence comparisons of nuclear small subunit rRNA genes, trypanosomes isolated from several fish species at different localities can be divided into at least 2 closely related types, designated Type A and Type B. A clone derived from a Type A isolate from carp (Cyprinus carpio) was used to study the anti-parasite immune response in specified pathogen-free outbred carp. Infection leads to an initial rise in parasitaemia in the blood followed by a sharp decline in all fish (acute phase). Thereafter, in some carp, parasites become undetectable both in the blood and in internal organs while, in others, low numbers can be found in the blood for up to 1 year (chronic phase). Fish that have controlled an acute infection with the clone are not only protected against an homologous challenge infection, but also against the infection with parasite lines derived from carp in the chronic phase of infection. Passive immunization experiments with IgM purified from serum of recovered carp indicate that the infection is controlled by antibodies. The anti-parasite antibody level in recovered carp remains high for many months although the parasitaemia is controlled at very low levels and the half life of IgM, t1/2=22·5 days, is comparatively short. The effective control of trypanosomes in laboratory infections is in contrast to the high prevalence in natural and farmed freshwater fish populations.

The great French helminthologist, Dujardin, appears to have been the first to suggest a grouping of the genus “Ascaris” according to the structure of the alimentary canal. As is, unhappily, only too well known to modern helminthologists, little attention was paid to internal structures by the earlier workers, whose numerous descriptions and classifications were based almost entirely upon external characters. It is now recognized that a natural system must be based on a survey of the whole structure of the animal, both external and internal, and a re-examination of many of the older species becomes extremely important.

The morphology of a micro-organism, Cytœcetes microti, new genus, new species, which invades the granulocytes and occasionally the lymphocytes, is described. It occurs naturally in the vole, Microtus pennsylvanicus, is transmissible to white-footed mice, Peromyscus leucopus and Peromyscus eremicus, the common tame mouse, the white rat, but inoculations of guinea-pigs. domestic rabbits, a kitten and young chickens have resulted negatively. The only pathological effect attributable thus far to this organism is an increase in the number of granulocytes found in certain organs such as the spleen and adrenals, and degenerative changes in the individual cell invaded. Splenectomy performed soon after the microscopic disappearance of Cytœcetes from the circulating blood may result in its reappearance, when it may occur in a considerable proportion of the granulocytes, but nevertheless in smaller numbers than at the height of early infection. Overwhelming infections have in no instance followed splenectomy. The probable relationship of the organism to Ægyptianella pullorum (Carpano, 1928) is pointed out, but grounds for placing it in a separate genus are presented.

Reproductive success of Gyrodactylus salaris from River Lierelva was compared experimentally on 3 stocks of salmon (12·5°C±0·2). Isolated fish from 2 susceptible Norwegian stocks (Rivers Lier and Alta) and 1 resistant Baltic stock of salmon (River Neva) were infected with a single gravid worm in order to record the temporal sequence of births and age at death of individual parasites. Establishment success (proportion of worms surviving to give birth) was generally low and mortality high, but significantly fewer worms survived on Neva (45% with mean survival of 3·5 days) compared to Alta and Lier fish (60%, mean survival 7·9 and 5·2 days, respectively). There was a dramatic difference in parasite fecundity between the host stocks: only 2 births occurred on Neva fish compared to third and fourth births on both Alta and Lier hosts. The timing of the first birth was more variable on Neva hosts and was significantly extended (mean 2·3 days) relative to that on Alta and Neva fish (1·8 days). However, timing of the second birth did not vary on any of the 3 salmon stocks. Age-specific mortality and fecundity data are consistent with exponential population growth of G. salaris on Alta and Lier fish but eventual extinction on Neva hosts. This is the first demonstration that gyrodactylids maintained on different host stocks exhibit variations in fecundity, development and mortality, which may in turn account for the variable virulence noted when G. salaris infects different salmonid hosts.

1. Studies, using serial sections and a method of numerical assessment of the, numbers of cercariae in the various tissues, have shown that cercarial entry occurs through the skin at any point along the length of the fish and also through the gills and pharynx in the head region. The distribution of penetration along the length of the body is not uniform but exhibits a marked concentration in the head region.

2. As the time after infection increases, this initial unimodal distribution is maintained and becomes even more restricted.

3. Nearly all the cercariae have localized in the eye 12–24 hr. after infection. The few that remain outside the eye after this period appear to be moribund and undergoing phagocytosis.

4. The majority of migrating cercariae are present in connective tissue and muscle. Very few occur in the blood system and even fewer in the other organs of the body. The numbers in the blood system show a local anterior concentration in the blood vessels anterior to the heart and in the region of the gills. It seems probable that the blood system does not form the major route of migration.

5. Entry into the eye may occur at any point.

6. Cercarial migration causes extensive tissue damage, but this is fatal only when major blood vessels are perforated and severe internal haemorrhage results. Interference with the nervous system and lateral line system may be the cause of the orientation disturbances which are sometimes noted within 12 hr. after infection.

7. It is suggested that migration through the tissues is achieved mainly by the action of the anterior spination and that the function of the penetration gland cells may be lubricatory and/or adhesive rather than lytic.

8. The restricted tissue distribution during migration and the retention of an essentially unimodal distribution of cercariae along the length of the body through-out the whole period of migration suggest that localization in the lens is not achieved by chance migration.

Data concerning the life cycle of the various species of the genus Trichuris are somewhat controversial. The present paper is devoted to the study of T. muris, a common parasite of the caecum of wild house-mice and rats. The possibility of transfer of T. muris in the laboratory mice would enable the author to solve various contradictory points.

The decline in faecal egg counts, characteristic of calves which have been experimentally infected with Ostertagia ostertagi, is analysed using a mathematical model in which parasite fecundity is assumed to be an inverse function of both the duration and intensity of infection. The model incorporates a description of the frequency distribution of mature parasites between hosts (which is less over-dispersed than is usual for many other helminth infections). The model provides a good overall description of the decline in faecal egg production observed during trickle and single infection experiments. The main discrepancy between a comparison of the model predictions and the results of the most detailed available series of trickle infection experiments occurs at the initial peak of egg production. The magnitude of this difference appears to be related to the worm burden at the peak of egg production. The possible mechanisms underlying density-dependent regulation of the fecundity of O. ostertagia are discussed.

We investigated the blood-feeding behaviour of a natural population of the human-feeding mosquito Anopheles punctulatus in Iguruwe, Papua New Guinea. In particular we investigated the relationship between the mosquitoes' blood-feeding behaviour and their infection by the malaria parasites Plasmodium falciparum and P. vivax. Female mosquitoes were caught at 4 times of the night, the amount of blood they had obtained was measured and their status of infection was evaluated. Among uninfected mosquitoes the bloodmeal size steadily increased through the night, possibly because they were progressively less likely to be disturbed by human activity as the night drew on. Infected mosquitoes, on the other hand, tended to feed maximally at all times of the night. This suggests that infected mosquitoes were more tenacious in their blood-feeding behaviour, being either less readily disturbed during a bout of feeding (and thus feeding longer) or more likely to return to continue their feed following disturbance (and thus feeding several times). Either change would increase the parasites' rate of transmission. We conclude that in this natural situation the two species of malaria parasites modified the mosquitoes' behaviour with the effect of increasing their own transmission.

Using data sets derived from published literature, the contribution of congeneric species to helminth component community richness is evaluated. Consideration of the frequency distribution of congeners in relation to host and parasite groups reveals that the distributions are unimodal, that singletons are the commonest class and that the frequency of occurrence of congeners decreases with increasing number of species per genus. Congeners may be found in any group of hosts or parasites, but are more common amongst cestodes of aquatic birds. Two patterns of occurrence of congeneric species are recognized: one in which from a few to multiple congeners are found within a single helminth genus, exemplified by dactylogyrid monogeneans and cloacinid nematodes, and the other in which there is a simultaneous occurrence of congenerics and confamilials such that there are several genera involved, but each represented by fewer species, exemplified by strongyles in horses. The question of whether these patterns can be considered examples of species flocks is discussed. We conclude that multiple congeners and species flocks are interesting phenomena but, except in isolated cases, they make insignificant contributions to community richness.

The body wall of Polymorphus minutus has been studied with the electron microscope and the structure of the various layers has been described.

The layers are the same in number as those seen with the light microscope, and pores have been found which penetrate the cuticle. Thus, the structure of the surface layers is such as would facilitate the absorption of nutrients.

It has been found that the cuticle and striped layer extend over the trunk spines, a feature which increases the area of the absorptive surface of the parasite.

The structure of the striped layer of the praesoma supports the theory that the praesoma body wall and lemnisci are involved in the absorption of fat.

Mitochondria have been detected in the felt and radial layers of the body wall and in the circular and longitudinal muscles.

The body wall of this acanthocephalan worm is entirely different from the body wall of trematodes, cestodes and parasitic nematodes.

We are grateful to Dr P. Tate for helpful discussions, Dr R. J. Skaer for criticism of the manuscript and to Professor J. D. Boyd for permission to use the electron microscope in the Department of Anatomy. Thanks are also due to Mr A. J. Page for technical assistance.

A group of 27 variable antigen type (VAT)-specific monoclonal antibodies (McAbs) have been made against metacyclic forms of a cloned stock of Trypanosoma brucei rhodesiense. In combination, these labelled in immunofluorescence 99·3% of trypanosomes in salivary probes from tsetse flies. The 0·7% of unlabelled trypanosomes were believed to be uncoated forms. The ability of a mixture of antibodies to kill metacyclics in vitro by complement-mediated lysis, thus neutralizing their infectivity for mice, was tested. The antibody mixture consisted of 24 McAbs plus 3 VAT-specific rabbit antisera. In 12 replicate experiments this mixture of antibodies prevented infection of mice. Parallel controls showed that neutralization was probably antibody-mediated and VAT specific. However, we have not been able to repeat these results on a long-term basis; this may be due to a loss of neutralizing activity by one of the McAbs. The successful neutralization experiments indicate that the number of VATs in the metacyclic repertoire of one stock of T. b. rhodesiense is limited to at most 27.

The blackcap (Sylvia atricapilla) is a common Palearctic migratory warbler, and haemosporidian parasites are common in this species. However, genetic and phenotypic diversity of haemosporidians in warblers has been insufficiently investigated and poorly linked. We addressed this issue by combining molecular and microscopy data for detection of pigment-forming haemosporidians of the genera Haemoproteus and Plasmodium. Blood samples from 498 blackcaps were collected at 7 different sites in Europe and investigated for these parasites by polymerase chain reaction (PCR)-based techniques and microscopic examination. In all, 56% of the birds were infected by at least 1 out of 25 distinct mitochondrial cytochrome b (cyt b) gene lineages of these haemosporidians. It is concluded that the blackcap is infected not only with blackcap specific haemosporidians, but also with Haemoproteus majoris, which is a host generalist and common in birds belonging to the Paridae. Haemoproteus pallidulus sp. nov. is described based on morphology of its blood stages and segments of the cyt b and dihydrofolate reductase/thymidylate synthase (DHFR-TS) genes. This study provides evidence that genetic diversity of haemosporidian parasites might be positively correlated with migratory strategies of their avian hosts; it also contributes to the value of both microscopy and molecular diagnostics of avian blood parasites.

Control of equine nematodes has relied on benzimidazoles (BZs), tetrahydropyrimidines and macrocyclic lactones. The intensive use of anthelmintics has led to the development of anthelmintic resistance (AR) in equine cyathostomins and Parascaris equorum. Field studies indicate that BZ and pyrantel resistance is widespread in cyathostomins and there are also increasing reports of resistance to macrocyclic lactones in cyathostomins and P. equorum. The unavailability of reliable laboratory-based techniques for detecting resistance further augments the problem of nematode control in horses. The only reliable test used in horses is the fecal egg count reduction test; therefore, more focus should be given to develop and validate improved methodologies for diagnosing AR at an early stage, as well as determining the mechanisms involved in resistance development. Therefore, equine industry and researchers should devise and implement new strategies for equine worm control, such as the use of bioactive pastures or novel feed additives, and control should increasingly incorporate alternative and evidence-based parasite control strategies to limit the development of AR. This review describes the history and prevalence of AR in equine nematodes, along with recent advances in developing resistance diagnostic tests and worm control strategies in horses, as well as giving some perspective on recent research into novel control strategies.

Eimeria arizonensis, E. albigulae and E. onychomysis, morphologically similar species from closely related murid rodents, were distinguished using nuclear rDNA ITS1 sequences obtained from multiple isolates of each taxon. ITS1 sequences were also obtained from 6 other species parasitizing murid rodents: E. falciformis, E. langebarteli, E. nieschulzi, E. papillata, E. separata and E. sevilletensis, and from E. reedi, a parasite of heteromyid rodents. Under parsimony and maximum likelihood analyses, the isolates of E. arizonensis, E. albigulae and E. onychomysis were differentiated as closely related, monophyletic lineages. Maximum likelihood pairwise distances between the latter species ranged from 7 to 12%, and distances within each species ranged from <1 to 5%; thus it is suggested that ITS1 genetic distances may be used to facilitate taxonomic differentiation of Eimeria spp. Against expectation, phylogenetic procedures placed E. reedi within the phylogeny of the Eimeria of murid rodents. ITS1 sequencing appears to provide data that can be used for taxonomic and phylogenetic studies on the speciose genus Eimeria, and may be especially useful when samples contain insufficient numbers of oocysts for other molecular-based methods, e.g. RAPD–PCR.

The abundance and diversity of parasites vary among different populations of host species. In some host-parasite associations, much of the variation seems to depend on the identity of the host species, whereas in other cases it is better explained by local environmental conditions. The few parasite taxa investigated to date make it difficult to discern any general pattern governing large-scale variation in abundance or diversity. Here, we test whether the abundance and diversity of gamasid mites parasitic on small mammals across different regions of the Palaearctic are determined mainly by host identity or by parameters of the abiotic environment. Using data from 42 host species from 26 distinct regions, we found that mite abundances on different populations of the same host species were more similar to each other than expected by chance, and varied significantly among host species, with half of the variance among samples explained by differences between host species. A similar but less pronounced pattern was observed for mite diversity, measured both as species richness and as the taxonomic distinctness of mite species within an assemblage. Strong environmental effects were also observed, with local temperature and precipitation correlating with mite abundance and species richness, respectively, across populations of the same host species, for many of the host species examined. These results are compared to those obtained for other groups of parasites, notably fleas, and discussed in light of attempts to find general rules governing the geographical variation in the abundance and diversity of parasite assemblages.