There can be no doubt that reasoning by analogy contributes enormously to the progress of Science by suggesting the hypotheses which form the basis of experimental investigation. But although it is useful, it is also dangerous and it is not infrequently the source of plausible but inaccurate and misleading catchwords.

Mice experimentally infected with the hydatid parasite Echinococcus granulosus (secondary echinococcosis), were used as spleen cell donors for hybridoma production. Two hybridomas were produced which secreted antibody with anti-E. granulosus cyst fluid (EgCF) activity. Radio-immunoassays comparing the binding of these hybridoma-derived antibodies to E. granulosus versus several other antigen preparations from sheep parasites showed that the antibodies had a high degree of specificity for the hydatid parasite. However, using a panel of clinically defined sheep sera in a competitive radio-immunoassay, the binding of the hybridoma-derived antibodies to EgCF was inhibited strongly by sera from sheep infected with the common parasites Fasciola hepatica and Taenia hydatigena. When the hybridoma-derived antibodies were conjugated to CNBr-activated Sepharose and the crude EgCF applied to the affinity column, the ‘run through’ antigen preparation showed a significant increase in specificity for experimental E. granulosus infection. A useful means of applying the hybridoma technology in the development of new immunodiagnostic reagents may be to select those murine hybridomas which produce high-affinity, cross-reacting antibodies and to use these antibodies in the processing of homologous antigen by affinity chromatography.

Infections with Theileria parva in the African buffalo are invariably asymptomatic, whereas infections in cattle usually result in clinical disease, the severity of which varies in different populations of cattle. The parasite exhibits antigenic heterogeneity, which in cattle manifests as differences between parasite strains in their cross-protective properties. A series of studies on T cell responses to T. parva in cattle have demonstrated that class I MHC-restricted cytotoxic T lymphocytes (CTL), specific for parasitized lymphoblasts, are important mediators of immunity. Cytotoxic T cell responses frequently display parasite strain-restricted specificities which appear to correlate with the capacity of strains to cross-protect. The strain specificity of CTL responses varies in animals immunized with the same parasite strain and is influenced by both host and parasite genotype. Recent studies have provided evidence that there is competition between epitopes for induction of CTL responses, which can result in a bias to strain-specific epitopes. These properties of the CTL response have important implications for vaccination. Thus, in designing a vaccine, it may be possible, by selecting parasite proteins containing appropriate CTL epitopes, to generate CTL responses that protect against a wide range of parasite strains. Although there are no comparable data on CTL responses in the buffalo, it is considered that the features of the immune response described for cattle would be advantageous for survival of parasite populations in the buffalo. Specifically, a bias in the immune responses to strain-specific determinants should favour establishment of infection in buffalo already carrying the parasite and allow fluctuation in the levels of different parasite strains during the course of persistent infection.

Seven species of marine fishes and three of fresh or brackish water Canadian fishes have yielded new or known Myxosporidia. The marine fishes were from St Andrews, New Brunswick and Halifax, Nova Scotia, places 250–275 miles apart by sea, and from the Labrador coast. The brackish and freshwater fishes were obtained in Montreal and the Salmon River, Nova Scotia.

Descriptions and illustrations are given of the morphology of five new species of Myxosporidia: Ceratomyxa urophysis, Myxoproteus myoxocephali, Myxidium myoxocephali, Myxosoma diaphana and Henneguya amiae.

Chloromyxum leydigi Mingazzini, C. granulosum Davis, Myxidium lieberkuhni Bütschli, Myxidium gadi Georgévitch and Zschokkella hildae Auerbach are recorded from new piscine hosts in Canada.

Some effects of the Myxosporidian infections, both macroscopic and microscopic, on their hosts are considered. Comparison of the effects of similar infections of Myxosporidia on allied fishes in Normandy and Eastern Canada has shown a general similarity between them.

The economic importance of some Myxosporidian infections of the edible fish examined is shown by parasitism of the cod, haddock and sculpin. Amia calva is also used for food in Montreal. The possibility of edible fishes acquiring Myxosporidian infections by way of their food is noted, with reference to the host-specificity of the Myxosporidia of Fundulus heteroclitus described by Bond.

The influence of environment on and powers of adaptation to different habitats exhibited by certain Myxosporidia is discussed.

Some remarks are made on the zoogeographical distribution of certain Myxosporidia and their piscine hosts.

The fine structure of the nervous system in the scolex and neck region of Hymenolepis nana has been investigated by transmission electron microscopy. A description of the gross neuroanatomy in these regions of the worm is presented. The ganglia, commissures and nerve cords consist of an incomplete cortex of nerve cell bodies, and a core of nerve fibres. A delimiting sheath or capsule is absent. The nerve cell bodies contain a single nucleus with a single nucleolus, mitochondria, many ribosomes, Golgi complexes and vesicles formed within the Golgi cisternae. Numerous sub-surface cisternae are present beneath the outer plasma membrane of the nerve cell body, and the inner surfaces of these cisternae are studded with ribosomes. Some of the cisternae run tangentially into the cytoplasm of the perikaryon, particularly in the vicinity of the Golgi complexes; both sides of these cisternae are studded with ribosomes. From each neuronal perikaryon arise one or more neurites that contain neurotubules, mitochondria, ribosomes and electron-lucent or dense-cored vesicles. Five types of vesicle have been distinguished on the basis of their size and content. The neurites are unmyelinated and form synapses in the neuropile; the synapses possess features typical of those where mechanical strength is of importance. Three types of sensory receptors have been observed in H. nana, two ciliated and one non-ciliated; the latter typically form double or triple nerve endings which terminate within the tegument.

The ability of haemocytes, from the haemolymph of the gastropod mollusc Lymnaea stagnalis, to recognize and eliminate the bacterium Aeromonas salmonicida was shown using an in vitro bacterial clearance assay. The assay employs a dye which is reduced by A. salmonicida in direct proportion to the number of viable bacteria resulting in a colour change which can be determined spectrophotometrically. Addition of cytochalasin B resulted in a marked decrease in bacterial clearance, implicating both intracellular and extracellular cytotoxicity of haemocytes. A comparison of haemocytes from uninfected snails and snails infected with the avian schistosome parasite Trichobilharzia ocellata showed that both juveniles and adults of L. stagnalis were susceptible to infection with T. ocellata. After exposure to the trematode for 1·5 h the haemocytes from these infected snails had an enhanced clearance capacity, whilst cells obtained from snails with 24–96 h infections showed decreased clearance of the bacteria, indicating suppression by the parasite. Haemocytes, as well as plasma, which was tested on haemocytes from uninfected snails, were used and hence a distinction was made between cell and humoralassociated effects. The results show that both cellular and humoral components of immunity were activated, then suppressed, following exposure to the parasite. Infection with T. ocellata seems to have a modulating effect on the bactericidal activity of the internal defence system of the snail host, L. stagnalis.

The characterization of four Trypanosoma vivax isolates from Colombia in South America showed that although minor phenotypic differences existed between them, these parasites are antigenically related and belong to a single serodeme. Characterization by isoenzyme assay, karyotyping and DNA probe analysis, showed the Colombian isolates to be more similar to the West African than to Kenyan T. vivax. There was, however, little serological cross-reactivity between South American and African groups of T. vivax. Although the T. vivax isolates from Colombia were pathogenic for dairy calves which showed the typical sign of progressive emaciation, these parasites failed to infect mice or tsetseand could not be cultivated as bloodstream forms in vitro.This study represents initial attempts to establish the phenotypic and serological diversity amongst T. vivax isolates from South America.

The development of resistance by the Houghton strain of Eimeria tenella (H) to monensin has been studied by serially passaging the strain in groups of 30 birds, each inoculated with 106 oocysts and given 100 p.p.m. of drug in the food. After 16 passages a line partially resistant to this concentration of monensin was produced. Passage of the line in birds medicated with 200 or 300 p.p.m. of monensin did not result in the acquisition of a greater degree of resistance. A further reduction in sensitivity to 100 p.p.m. monensin was obtained, however, when the line was serially passaged in 15 groups of 6 birds each given 3 × 106 oocysts. Five passages in the absence of monensin resulted in restoration of sensitivity, suggesting that the resistance developed was not stable. The pathogenic effects of the line that had been passaged in chickens given 300 p.p.m. of monensin were less than those of the parent line.

As there is little evidence of pollution affecting the health of fish and shellfish on a global scale, this paper attempts to put into perspective the pollution/fish disease relationship by reviewing examples of studies and reports in the historic and current literature. Although there is no dispute that pollution can affect the health of aquatic organisms under laboratory conditions and may be responsible for the decline of populations of such animals in some inland waters and some estuaries, most of the evidence for pollution causing or increasing disease in fish in open waters is circumstantial. Historical data proves that almost all fish and shellfish diseases known today have been described since the end of the last century. However, it is also known that water pollution, especially in inland waters, has for the past 400-500 years been the result of urbanization and industrialization. This has resulted in some major rivers becoming devoid of or deficient in fish stocks. The concern that pollution may influence the health status of fish and shellfish stocks has increased over the past 20 years. Initial attention was paid to epidermal diseases, including fin-rot in demersal fish, and protozoan diseases in molluscs in the heavily polluted bays and estuaries in North America. As the interest in this subject spread, it became political, and often controversial, especially amongst the North Sea countries. The disagreements have largely been settled amongst scientists because international bodies, such as the International Council for Exploration of the Sea (ICES), established workshops to investigate sampling methods and disease-reporting techniques. Recommendations from those workshops have contributed to some form of standardization for field work and the subject, although largely subjective, has some objective approaches which are described. As there are variable, interacting biological and physical influences in the aquatic environment, it is difficult to establish the background prevalences of diseases in populations offish and shellfish. Examples of the influences of climatic changes are presented, and these show that short-term catastrophes can be directly related. However, a more long-term problem is water acidification resulting largely from anthropogenic activities. In parts of Scandinavia this has, and is, leading to decimation offish stocks in inland waters. In general, diseases in fish and shellfish are very localized, but there is concern amongst scientists that certain cancers, especially liver tumours, occurring in demersal fish inhabiting polluted estuarine and coastal waters, are related to the release of chemicals, e.g. hydrocarbons, pesticides and heavy metals. This subject is discussed in detail, with examples of the author's own studies in North Sea fish. It is concluded that cancers in fish are of extremely low prevalence, and only present in a very few species, and then only in the oldest animals. Though changes in disease pattern may well be an indication of adverse environmental effects, further research is necessary for conclusive evidence.

Microfilariae belonging to the genera Brugia, Loa and Wuchereria have been stained by a wide variety of histochemical methods. The results are recorded in eight Tables.

The sheath of the microfilaria contains polyanionic material, probably polysulphate, periodate reactive mucosubstance, sulphur-protein and complex lipids. The fluid within the sheath is also polyanionic.

The cuticle of the microfilaria is stabilized by disulphide bonds possibly in a collagen but it was not possible to demonstrate collagen by staining. The cuticle also contains a periodate reactive G mucosubstance and complex lipids. The annular grooves of the cuticle also contain a periodate unreactive mucosubstance. Certain areas of the cuticle, around the excretory pore, the pores of the Schwanzgebilde, and the cephalic structures - oral ring, hook and spines - are hardened by deposition of a keratinous scleroprotein. Some reactions of the cuticle may be masked by the presence of basic protein.

The excretory vesicle contains polyanionic material but there was no clear evidence that the polyanionic material within the fluid in the sheath came from the excretory vesicle. The excretory vesicle, the anal vesicle and the subcuticular cells contain periodate reactive G mucosubstance. Most RNA staining was found in the excretory vesicle, the excretory cell, the anal vesicle, the rectal cells and the G cell.

The pharyngeal thread, the Innenkörper, the rectal cells and the anal vesicle represent the modified gut of this first stage larva. The pharyngeal thread appears to consist largely of a protein-mucosubstance complex that can be unmasked by oxidation. The Innenkörper contains a basic protein and acidic mucosubstance, possibly sialomucin, complex that can be unmasked by adjusting the electrolyte concentration of the staining media.

The relevance of some of these techniques in the analysis of possibly unique invertebrate structures is discussed briefly.

We thank Dr D. A. Denham, Mr P. R. N. Pester and Dr T. Ponnudurai in particular, and many other correspondents, for supplying us with microfilariae for staining. This work was supported by a grant from the Medical Research Council of Great Britain.

Intact, viable adults, infective and newborn larvae of Trichinella pseudospiralis were surface labelled with 125I by the chloramine T method and labelled proteins were compared with those obtained from equivalent stages of T. spiralis. Electron-microscope autoradiography determined that labelled proteins were restricted to the cuticle for all stages of both isolates. Comparative polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDS–PAGE), using thin gradient gel slabs, of proteins obtained from each stage, demonstrated that the profile of surface-labelled proteins of T. pseudospiralis were restricted in number, stage specific, and similar to equivalent proteins of T. spiralis both in size and in their organization into aggregates. The stage-specific profiles of surface-labelled proteins derived from newborn larvae were indistinguishable, but differences were noted between adults and infective larvae of the two isolates. These differences in protein structure were confirmed by two dimensional mapping of tryptic peptides. Stage-specific profiles were also obtained when [35S]methionine biosynthetically labelled secretions of the 3 stages of T. pseudospiralis were compared by SDS–PAGE. Comparison of the profiles obtained with secretions for respective stages of T. spiralis again failed to distinguish newborn larvae, but adults and infective larvae of T. spiralis and T. pseudospiralis displayed a mixture of common and species-specific proteins. These findings are discussed in relation to the different pathology associated with infection with two isolates.

Chicory is a perennial crop that has been investigated as a forage source for outdoor-reared ruminants and pigs, and has been reported to have anthelmintic properties. Here, we investigated in vitro anthelmintic effects of forage chicory-extracts against the highly prevalent swine parasites Ascaris suum and Oesophagostomum dentatum. Methanol extracts were prepared and purified from two different cultivars of chicory (Spadona and Puna II). Marked differences were observed between the anthelmintic activity of extracts from the two cultivars. Spadona extracts had potent activity against A. suum third (L3) and fourth (L4) – stage larvae, as well as O. dentatum L4 and adults, whereas Puna II extracts had less activity against A. suum and no activity towards O. dentatum L4. Transmission-electron microscopy of A. suum L4 exposed to Spadona extracts revealed only subtle changes, perhaps indicative of a specific anthelmintic effect rather than generalized toxicity. Ultra-high liquid chromatography-mass spectrometry analysis revealed that the purified extracts were rich in sesquiterpene lactones (SL), and that the SL profile differed significantly between cultivars. This is the first report of anthelmintic activity of forage chicory towards swine nematodes. Our results indicate a significant anthelmintic effect, which may possibly be related to SL composition.

Parasite ecologists are often interested in the repeatability of patterns in parasite communities in space and/or time, because of implications for the dynamics of host-parasite interactions. Field studies usually examine temporal and spatial variation in isolation or limit themselves to a small number of host populations. Here, we studied the macroparasite communities of 12 populations of three-spined stickleback, Gasterosteus aculeatus L., on North Uist, Scotland, separated by small geographical distances, during the breeding season in 2 consecutive years (2007 and 2008) to determine: (1) the extent of spatial variation in macroparasite communities, (2) whether this variation is consistent across years, and (3) whether habitat characteristics can explain differences in macroparasite community composition among populations. We found substantial variation in parasite communities among populations. Generally, measures of parasite community composition were higher in 2008 than in 2007, but this effect of year was consistent across populations, such that the relative differences in these measures among populations changed little between years. These data suggest that there is short-term stability in the spatial variation in macroparasite communities of North Uist sticklebacks. However, none of the 5 habitat characteristics measured explained spatial variation in any measure of parasite community composition.

The nervous system of young and adult Amphilina foliacea was studied with immunocytochemical, electron microscopical and spectrofluorometrical methods. The general neuroanatomy is described in detail. New data on the structure and development of the brain were obtained. The 5-HT and GYIRFamide-immunoreactivities occur in separate sets of neurones. The innervation of the reproductive organs is described. The fine structure of 2 types of neurones in the CNS, a sensory neurone, a ‘glial’ cell type, the neuropile and the synapses are described. The level of 5-HT varies between 0·074 and 0·461 μg/g wet weight. This is the first detailed study of the nervous system of A. foliacea. Earlier data on the structure of the nervous system in A. foliacea published in Russian are introduced into the discussion. The study provides data that can be used when considering the phylogenetic position of Amphilinidea.

To address the molecular diversity and occurrence of pathogenic species of the genus Entamoeba spp. in wild non-human primates (NHP) we conducted molecular-phylogenetic analyses on Entamoeba from wild chimpanzees living in the Issa Valley, Tanzania. We compared the sensitivity of molecular [using a genus-specific polymerase chain reaction (PCR)] and coproscopic detection (merthiolate-iodine-formaldehyde concentration) of Entamoeba spp. We identified Entamoeba spp. in 72 chimpanzee fecal samples (79%) subjected to species-specific PCRs for six Entamoeba species/groups (Entamoeba histolytica, Entamoeba nuttalli, Entamoeba dispar, Entamoeba moshkovskii, Entamoeba coli and Entamoeba polecki ST2). We recorded three Entamoeba species: E. coli (47%), E. dispar (16%), Entamoeba hartmanni (51%). Coproscopically, we could only distinguish the cysts of complex E. histolytica/dispar/moshkovskii/nuttalli and E. coli. Molecular prevalence of entamoebas was higher than the prevalence based on the coproscopic examination. Our molecular phylogenies showed that sequences of E. dispar and E. coli from Issa chimpanzees are closely related to sequences from humans and other NHP from GenBank. The results showed that wild chimpanzees harbour Entamoeba species similar to those occurring in humans; however, no pathogenic species were detected. Molecular-phylogenetic methods are critical to improve diagnostics of entamoebas in wild NHP and for determining an accurate prevalence of Entamoeba species.

Concentrations of the elements As, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, Sn, V, Zn were analysed by inductively coupled plasma mass spectrometry (ICP-MS) in the acanthocephalan Pomphorhynchus laevis and its fish host Barbus barbus. A total of 27 barbels were collected from the Danube River in autumn 2006 close to the town Kozloduy (685 river kilometer) on the Bulgarian river bank. Fish were divided into 3 groups. According to their P. laevis infrapopulation size hosts were considered as heavily infected (>100 worms per fish) and lightly infected (<20 worms per fish). The third group was used to compare heavy metal concentrations between male and female P. laevis. The 5 elements As, Cd, Cu, Pb and Zn were detected in significantly higher concentrations in parasites compared to host tissues (muscle, intestine, liver). According to the calculated mean bioconcentration factors, 3 more elements (Co, Mn, V) showed usually higher concentrations in P. laevis. Comparisons between heavily and lightly infected fish revealed significant differences only for V with higher concentrations for the heavily infected group. Concerning sex-specific metal accumulation V and Zn showed significant differences (V, at P<0·05; Zn, at P=0·05), with higher levels of both metals in females of P. laevis. Our results suggest that – for the metals analysed – the size of the parasite infrapopulation plays no role in the degree of metal accumulation. Similarly, parasite sex seems not to be a crucial factor for metal accumulation in the parasites. Thus, for metal monitoring purposes there is no need to take these aspects into account, which makes the use of parasites as bioindicators more applicable.

We tested the hypothesis that compositional and/or phylogenetic dissimilarity of host assemblages affect compositional and/or phylogenetic dissimilarity of parasite assemblages, to different extents depending on scale, using regional surveys of fleas parasitic on small mammals from 4 biogeographical realms. Using phylogenetic community dissimilarity metric, we calculated the compositional and phylogenetic dissimilarity components between all pairs of host and parasite communities within realms and hemispheres. We then quantified the effect of compositional or phylogenetic dissimilarity in host regional assemblages, and geographical distance between assemblages, on the compositional or phylogenetic dissimilarity of flea regional assemblages within a realm, respectively. The compositional dissimilarity in host assemblages strongly affected compositional dissimilarity in flea assemblages within all realms and within both hemispheres. However, the effect of phylogenetic dissimilarity of host assemblages on that of flea assemblages was mostly confined to the Neotropics and Nearctic, but was detected in both the Old and New World at the higher scale, possibly because of phylogenetic heterogeneity in flea and host faunas between realms. The clearer effect of the compositional rather than the phylogenetic component of host community dissimilarity on flea community dissimilarity suggests important roles for host switching and ecological fitting during the assembly history of flea communities.

Recent work has shown that mice with subclinical parasitic infections suffer impaired spatial learning and memory, as assayed in an open-field water maze. Although the mechanism underlying this effect is not clear, the phenomenon has been reported following infection with both a protozoan parasite (Eimeria vermiformis) and a gastrointestinal nematode (Heligmosomoides polygyrus). In a variety of experiments, we examined the effects of a different gastrointestinal nematode, Strongyloides ratti, on the ability of rats and mice to learn a spatial or a discrimination task. Animals were tested at various stages post-infection, with different levels of infection, using different lines of S. ratti and with varying experimental protocols. All animals learned the tasks, but we found no evidence of an effect of S. ratti infection on learning or memory. Even rats infected with approximately 5000 S. ratti larvae, a dose which has an impact on rat body size, showed no deficit in learning ability. Various reasons for the conflict between our results and those previously reported for E. vermiformis and H. polygyrus are discussed. Our results show that impaired learning and memory following parasitic infection is not a ubiquitous or at least easily replicated phenomenon.

This study compared genetic diversity of Toxoplasma gondii isolates from Portugal, Austria and Israel. For this, we genotyped 90 T. gondii isolates (16 from Portugal, 67 from Austria and 7 from Israel) using 10 nested PCR-restriction length polymorphism (RFLP) genetic markers and 15 microsatellite (MS) markers. By PCR-RFLP typing, 7 isolates from Portugal chickens were identified as type II (ToxoDB #1 or #3), 4 were type III (ToxoDB #2) and the remaining 4 isolates have unique genotype pattern were designated as ToxoDB #254. One mouse virulent isolate from a bovine fetus (Bos taurus) in Portugal was type I (ToxoDB #10) at all loci and designated as TgCowPr1. All 67 isolates from Austria and 7 from Israel were type II (ToxoDB #1 or #3). By MS typing, many additional genetic variations were revealed among the type II and type III isolates. Phylogenetic analysis showed that isolates from the same geographical locations tend to cluster together, and there is little overlapping of genotypes among different locations. This study demonstrated that the MS markers can provide higher discriminatory power to reveal association of genotypes with geographical locations. Future studies of the type II strains in Europe by these MS markers will be useful to reveal transmission patterns of the parasite.

To address whether a fish host is involved in the life cycles of malacosporeans of the genus Buddenbrockia, cohabitation experiments with different bryozoan and fish species were conducted. Samples were analysed by malacosporean-specific PCR, partial sequencing of the 18S rDNA, and light and electron microscopy. Co-habitation challenges with bryozoans resulted in malacosporean infections detected mainly in the kidney of common carp (Cyprinus carpio) and minnow (Phoxinus phoxinus). Sequences of the minnow parasite and of worm-like Buddenbrockia stages in Plumatella repens were identical and showed 99·5% similarity to Buddenbrockia plumatellae and 96·3% similarity to the sequence obtained from carp. One sample, comprising 4–5 zooids of statoblast-raised bryozoans cohabitated with infected carp was PCR-positive, but no overt infection could be observed in the remaining colony. Light and electron-microscopy of kidney samples of infected minnows revealed single cells within kidney tubules, whereas in carp, sporogonic stages were found in kidney tubules. Phylogenetic analysis of the Buddenbrockia spp. known to date placed the carp-infecting species at the base of the B. plumatellae clade, but low posterior probability makes this node questionable. The present study showed that Buddenbrockia spp. were able to infect cyprinid fish, showing stages in kidney-tubules strikingly similar to those of T. bryosalmonae.