The intestinal parasite community of Arctic foxes (Vulpes lagopus) on the Svalbard archipelago in the High Arctic was investigated in relation to the abundance and distribution of intermediate hosts. Five species of cestodes (Echinococcus multilocularis, Taenia crassiceps, Taenia polyacantha, Taenia krabbei and Diphyllobothrium sp.), ascaridoid nematodes and one unidentified acanthocephalan species were found. The cestodes E. multilocularis, T. crassiceps and T. polyacantha all showed a decreasing prevalence in the fox population with increasing distance from their spatially restricted intermediate host population of sibling voles (Microtus levis). In addition, the prevalence of E. multilocularis in a sample from the vole population was directly related to the local vole abundance. The cestode T. krabbei uses reindeer as intermediate host, and its prevalence in female foxes was positively related to the density of reindeer (Rangifer tarandus platyrhyncus). Finally, the prevalence of the ascaridoid nematodes also decreased with increasing distance from the vole population, a finding that is consistent with the idea that voles are involved in transmission, most likely as paratenic hosts. The prevalence of the remaining species (Diphyllobothrium sp. and an unidentified acanthocephalan) was very low. We conclude that the distribution and abundance of intermediate host structure the gastrointestinal parasite community of the Arctic fox on the Svalbard archipelago.

The adult of P. crucibulum is redescribed to form a basis for comparison with the cercaria and metacercaria. Particular emphasis is given to the structure and function of the rhynchus, digestive system and reproductive system. Some features, notably prepharyngeal glands and spematophores, have not previously been recorded in this species.

The sporocyst and cercaria which were found in Mytilus edulis are described for the first time. Out of 6907 mussels examined from Borth Rocks, Cardigan Bay, 0·26% were infected with P. crucibulum and 0·06 % with P. squamatus. The cercaria of the latter is redescribed on a comparative basis with that of P. crucibulum, to avoid confusion. The two cercariae are clearly distinguished by three features – flame-cell formula, shape of the excretory vesicle, and structure of the tail stem (this being bilobed in P. crucibulum and trilobed in P. squamatus). The significance of the two types of tail in securing attachment to the second intermediate host is discussed.

Metacercariae of P. crucibulum were obtained experimentally in ‘O’ group specimens of Scophthalmus maximus. Three other species of fish, namely Limanda limanda, Onus mustelus and Gobius minutus were also successfully infected. The metacercariae did not develop in the following fish: S. rhombus, Pleuronectes platessa, Cottus bubalis and Blennius pholis. Possible mechanisms which might account for host specificity within Pleuronectidae and Scophthalmus are suggested.

The development of the metacercaria in the connective tissues and musculature of S. maximus was followed over a period of 10 months. Within 1 month of infection the hyaline cyst of parasitic origin breaks down, enabling the parasite to feed directly on the host tissues. This feature is thought to account for the advanced development of the metacercaria, which 1 month after infection could clearly be identified with the adult on the basis of comparative morphology, and at 2 months resembles the adult in every respect except the development of the vitellaria. Egg production only occurs within the intestine of Conger conger, the definitive host.

Similarities in the immunobiology of different parasitic worm infections indicate that co-evolution of humans and helminths has shaped a common anti-helminth immune response. However, recent in vitro and immuno-epidemiological studies highlight fundamental differences and plasticity within host-helminth interactions. The ‘trade-off’ between immunity and immunopathology inherent in host immune responses occurs on a background of genetic polymorphism, variable exposure patterns and infection history. For the parasite, variation in life-cycle and antigen expression can influence the effector responses directed against them. This is particularly apparent when comparing gastrointestinal and tissue-dwelling helminths. Furthermore, insights into the impact of anti-helminthic treatment and co-infection on acquired immunity suggest that immune heterogeneity arises not from hosts and parasites in isolation, but also from the environment in which immune responses develop. Large-scale differences observed in the epidemiology of human helminthiases are a product of complex host-parasite-environment interactions which, given potential for exposure to parasite antigens in utero, can arise even before a parasite interacts with its human host. This review summarizes key differences identified in human acquired immune responses to nematode and trematode infections of public health importance and explores the factors contributing to these variations.

The chick embryo proved to be an eminently suitable medium for immunological studies on E. tenella infection, some of the difficulties encountered in the normal host, the hatched chicken, being circumvented.

Adoptive transfer of immunity to E. tenella infections in the chick embryo was obtained with antibodies and with cells from caecal tonsils. Protective factors (antibodies) were demonstrated in the serum of fowls which had been infected with E. tenella and in their progeny. Suspensions of caecal tosnil cells inoculated on to the CAM of developing chick embryos reduced the extent of subsequent infections with E. tenella and this was particularly marked when the cell donors had been immunized with E. tenella.

Serum globulin protected only when the donors were becoming immune, i.e. after the third inoculum of E. tenella oocysts. The experiment was not continued to the point at which the serum donors were ‘solidly immune’, when previous attempts to protect passively with serum have failed.

Maternally transmitted protection was demonstrated in embryos only at the time at which peak protection was afforded by serum globulin, but this is probably an unsatisfactory method of testing since antibodies are not present in allantoic fluid until late in incubation, when coccidial infections are already well established.Some reduction in the oocyst output of the progeny of immunized hens was found when these were challenged at 4 days of age.

The protection given by the inoculation of suspensions of cells from the caecal tonsils may have resulted from the production of antibodies by these cells or from their interaction with the parasite in some form of cell-mediated immune mechanism.

We are grateful to Mrs Patricia Hesketh, Mr Martin Shirley and Mr Ron Waters for technical assistance and to Mr Peter Townsend for care of the animals.

This study investigated protease activities in a crude extract and in vitro excretion/secretion (E/S) products of Philasterides dicentrarchi, a ciliate fish parasite causing economically significant losses in aquaculture. Gelatin/SDS–PAGE analysis (pH 4, reducing conditions) detected 7 bands with gelatinolytic activity (approximate molecular weights 30–63 kDa) in the crude extract. The banding pattern observed in analysis of E/S products was practically identical, except for 1 low-molecular-weight band detected in the crude extract but not in the E/S products. In assays with synthetic peptide p-nitroanilide substrates, the crude extract hydrolysed substrates characteristic of cysteine proteases, namely Z-Arg-Arg pNA, Bz-Phe-Val-Arg pNA and Z-Phe-Arg pNA. These activities were strongly inhibited by the cysteine protease inhibitor E-64 and by Ac-Leu-Val-Lys aldehyde, a potent inhibitor of cysteine proteases of the cathepsin B protease subfamily. The proteases present in the crude extract degraded both type-I collagen and haemoglobin in vitro, consistent with roles in tissue invasion and nutrition respectively. Again, E-64 completely (collagen) or markedly (haemoglobin) inhibited this degradation. Finally, the histolytic activity of the ciliate in turbot fibroblast monolayers was strongly reduced in the presence of E-64, confirming the importance of secreted cysteine proteinases in the biology of Philasterides dicentrarchi.

Hookworm infections, as assessed by counting worms expelled following anthelmintic treatment and by egg output, were found to be of low prevalence and intensity in a South Indian fishing community. The initial overall prevalence of infection in the community was 43%, and the average burden was estimated at 2·2 hookworms per person. The age profiles of prevalence and intensity differed between males and females, with the latter harbouring significantly higher levels of infection. Children of both sexes under 10 years of age rarely harboured hookworms. Treatment with pyrantel pamoate was estimated to be 91% effective in clearing hookworm infections. Egg counts made on stools collected during an 11-month period of reinfection indicated that female patients became reinfected soon after treatment, while little hookworm egg excretion was observed in males during the observation period following treatment. Females acquired a significantly higher number of worms during the reinfection period compared with males, although the average burden in females reached only 28% of the initial, pre-treatment level. The hookworm population consisted of predominantly Necator americanus, and less than 10% of Ancylostoma duodenale. The parasites were highly aggregated within the host population with 10% of the community harbouring over 65% of the total hookworms. Low values of the negative binomial aggregation parameter, k, (indicating extreme over-dispersion) were recorded in groups stratified by age and sex. Highly significant positive correlations were observed between the initial (pre-treatment) and reinfection worm burdens of female (but not of male) patients. It is suggested that occupational practices related to walking through areas contaminated with hookworm larvae play an important role in generating the observed patterns of infection within this community.

Mice infected with Babesia rodhaini can be cured with a single injection of Diampron and are immune to challenge with the same species. Mice infected with B. microti recover naturally from their infections and are also immune to challenge. The immunity extends to the heterologous species in both infections. In some cases parasites persist at a low level after recovery but in others the immunity is of a true sterile type. Immunity once established is unaffected by splenectomy in mice which have recovered from B. rodhaini and challenged with either B. rodhaini or B. microti.

We wish to express our thanks to May and Baker Ltd. who kindly provided us with the Diampron used in these experiments.

A survey of the relatively few anthomyid types described in this paper alone is sufficient to show that the external form of the egg may differ greatly from species to species. It would be interesting to find out if these differences are related in any way to the subsequent development or habits of the larvae.

The negative consequences of parasitic infection (virulence) were examined for two lizard malaria parasite—host associa tions: Plasmodium agamae and P. giganteum, parasites of the rainbow lizard, Agama agania, in Sierra Leone, West Africa; and P. mexicanum in the western fence lizard, Sceloporus occidentalis, in northern California. These malaria species vary greatly in their reproductive characteristics: P. agamae produces only 8 merozoites per schizont, P. giganteum yields over 100, and P. mexicanum an intermediate number. All three parasites appear to have had an ancient association with their host. In fence lizards, infection with malaria is associated with increased numbers of immature erythrocytes, decreased haemoglobin levels, decreased maximal oxygen consumption, and decreased running stamina. Not affected were numbers of erythrocytes, resting metabolic rate, and sprint running speed which is supported by anaerobic means in lizards. Infected male fence lizards had smaller testes, stored less fat in preparation for winter dormancy, were more often socially submissive and, unexpectedly, were more extravagantly coloured on the ventral surface (a sexually dimorphic trait) than non-infected males. Females also stored less fat and produced smaller clutches of eggs, a directly observed reduction in fitness. Infected fence lizards do not develop behavioural fevers. P. mexicanum appears to have broad thermal buffering abilities and thermal tolerance; the parasite's population growth was unaffected by experimental alterations in the lizard's body temperature. The data are less complete for A. agama, but infected lizards suffered similar haematological and physiological effects. Infected animals may be socially submissive because they appear to gather less insect prey, possibly a result of being forced into inferior territories. Infection does not reduce clutch size in rainbow lizards, but may lengthen the time between clutches. These results are compared with predictions emerging from several models of the evolution of parasite virulence. The lack of behavioural fevers in fence lizards may represent a physiological constraint by the lizards in evolving a thermal tolerance large enough to allow elimination of the parasite via fever. Such constraints may be important in determining the outcome of parasite—host coevolution. Some theory predicts low virulence in old parasite—host systems and higher virulence in parasites with greater reproductive output. However, in conflict with this argument, all three malarial species exhibited similar high costs to their hosts.

A key part of the life cycle of an organism is reproduction. For a number of important protist parasites that cause human and animal disease, their sexuality has been a topic of debate for many years. Traditionally, protists were considered to be primitive relatives of the ‘higher’ eukaryotes, which may have diverged prior to the evolution of sex and to reproduce by binary fission. More recent views of eukaryotic evolution suggest that sex, and meiosis, evolved early, possibly in the common ancestor of all eukaryotes. However, detecting sex in these parasites is not straightforward. Recent advances, particularly in genome sequencing technology, have allowed new insights into parasite reproduction. Here, we review the evidence on reproduction in parasitic protists. We discuss protist reproduction in the light of parasitic life cycles and routes of transmission among hosts.

The possible existence of strain and breed differences in the response of sheep to primary infections with Haemonchus contortus was examined by comparing the establishment and pathogenic effects of the parasite in Scottish Blackface and Finn Dorset sheep grouped according to haemoglobin type and infected with 7–10000 3rd-stage larvae. Homozygous haemoglobin A-type sheep of both breeds had lower worm burdens and faecal egg outputs, and suffered less severe clinical and pathophysiological disturbances than animals homozygous for haemoglobin B. In addition, Scottish Blackface sheep displayed similar advantages over Finn Dorsets with the same haemoglobin type and variations in the severity of the disease as judged by a variety of pathophysiological indices correlated closely with parasite numbers. It was therefore concluded that genetic resistance operated primarily against worm establishment and that, barring the unlikely involvement of non-specific physiological factors, this was controlled by the immune response elicited. The nature of this response is unknown, but appeared to operate only against the larval stages, since the size and metabolic activities of the surviving worms were similar in all animals. In a subsequent experiment, designed to examine the response of Scottish Blackface sheep to heavy infection (45000 larvae), there was no correlation between worm establishment and haemoglobin type. This was possibly due to a delayed immune response arising from exposure to excessive amounts of antigen.

The subsets of lymphocytes and cytokines regulating the site-specific immune response in experimental cysticercosis (Taenia crassiceps) are not known. This study investigated the cells present at the site of infection (PECs) using flow cytometry and measured the cytokines produced by these cells through 50 days of infection. The results showed an expansion of B220+CD5+, B220+CD5−, αβTCR+CD4+ and CD8+ cells coincident with a transient increase in IL-10 production. After the initial increase, the percentage of B220+ CD5− and helper T cells decreased with a concomitant decrease in IL-10 production. CD8+ T cells continued to increase throughout infection and γδTCR+ cells increased after 10 days of infection. PECs demonstrated an increased IFN-γ and IL-4 production throughout infection when stimulated with larval antigens. Because a Th2-type polarization has been shown for spleen cells from infected BALB/c mice, cytokine profiles of spleen cells and PECs in response to ConA and larval antigens were compared. ConA and antigen-specific stimulation of spleen cells from 50-day-infected mice produced increased amounts of IL-10 while PECs showed a decreased IL-10 production suggesting that anatomically distinct lymphoid populations produce different cytokines and promote different types of responses. Surprisingly, late in infection the levels of IL-4 and IFN-γ in serum increased substantially (460-fold and 100-fold, respectively). The systemic immune response of BALB/c mice during experimental cysticercosis, therefore, is a mixed Th1/Th2-type response.

Peptides belonging to the FMRFamide family are widely distributed amongst invertebrates. We report here on the isolation of the FMRFamide neuropeptide AF2 (Lys-His-Glu-Tyr-Leu-Arg-Phe-NH2) from the parasitic nematode Haemonchus contortus. Immunocytochemical techniques showed that FMRFamide-like material was distributed in several regions of these organisms including nerve cords and cell bodies of the central nervous system. AF2 was isolated using a method that employed 6 steps of reverse-phase HPLC. The concentration of AF2 in this organism was approximately 30 pmol/g of nematode.

Identification of parasite species is particularly challenging in larval and juvenile hosts, and this hampers the understanding of parasite acquisition in early life. The work described here employs a new combination of methods to identify parasite species and study parasite succession in fry of perch (Perca fluviatilis) from Lake Constance, Germany. Classical morphological diagnostics are combined with sequence comparisons between parasite life-stages collected from various hosts within the same ecosystem. In perch fry at different stages of development, 13 different parasite species were found. Incomplete morphological identifications of cestodes of the order Proteocephalidea, and trematodes of the family Diplostomatidae were complemented with sequences of mitochondrial DNA (cytochrome oxidase 1) and/or nuclear (28 s rDNA) genes. Sequences were compared to published data and used to link the parasites in perch to stages from molluscs, arthropods and more easily identifiable developmental stages from other fishes collected in Lake Constance, which both aided parasite identification and clarified transmission pathways. There were distinct changes in parasite community composition and abundance associated with perch fry age and habitat shifts. Some parasites became more abundant in older fish, whereas the composition of parasite communities was more strongly affected by the ontogenetic shifts from the pelagic to the littoral zone.

Some Kudoa species display variations in the number of polar capsules in spores within an individual pseudocyst. Nonetheless, there is usually a dominant morphotype which forms a significant element of diagnosis. In 2007, a Kudoa isolate from whiting (spores with 5 (dominant) or 6 (minor) polar capsules) was characterized by Burger et al. (2007) as being 100% identical in SSU rDNA to Kudoa yasunagai (spores with 7 polar capsules) from a halibut, despite its obvious morphological differences. The authors hypothesized that either SSU rDNA had reached its level of resolution or that the genetic identity revealed conspecificity. To further investigate these hypotheses, SSU and LSU rDNA sequence data were coupled with principal components, correlation, and regression analyses of morphometric data from different kudoid isolates that infect brain tissue to determine the relationships between spore morphotypes and different kudoid isolates. The trends in morphometrics between the spores of particular isolates were so similar that it was concluded that the molecular results did indicate conspecificity rather than SSU reaching its level of resolution. This phenotypic influence on a significant diagnostic character within the Kudoidae has a major impact on the diagnosis of this, and potentially other, pathogenic species.

Faecal samples were obtained from 433 wild birds being treated in wildlife recovery centres in Galicia (Northwest Spain), between February 2007 and September 2009. The birds belonged to 64 species representing 17 different orders. Giardia cysts and Cryptosporidium oocysts were detected by an immunofluorescence antibody test and identified at the molecular level by established PCR-sequencing methods. The overall prevalence of Giardia was 2·1% and that of Cryptosporidium, 8·3%. To our knowledge, this is the first description of Giardia sp. in Tyto alba and Caprimulgus europaeus; and of Cryptosporidium sp. in Apus apus, Athene noctua, C. europaeus, Falco tinnunculus, Morus bassanus, Parabuteo unicinctus and Strix aluco. Furthermore, the first PCR-sequence confirmed detection of Giardia duodenalis assemblage B in, Buteo buteo, Coturnix coturnix and Pica pica; G. duodenalis assemblage D in Garrulus glandarius; and G. duodenalis assemblage F in Anas platyrhynchos; Cryptosporidium parvum in Accipiter nisus, B. buteo, Milvus migrans, Pernis apivorus and P. pica; and Cryptosporidium meleagridis in Streptopelia turtur. The study findings demonstrate the wide spread of Giardia and Cryptosporidium between wild birds.

Objective. The aim of this work was to study the prevalence and genetic diversity of Babesia in Ixodes persulcatus ticks and small mammals from Ural and Siberia in Russia. Methods. In total, 481 small mammals and 922 questing adult I. persulcatus from North Ural (Sverdlovsk region) and West Siberia (Novosibirsk region) were examined for the presence of Babesia by nested PCR based on the 18S rRNA gene. Results. Babesia microti of the ‘Munich’-type was found in 36·2% of blood samples of the small mammals from the Sverdlovsk region and B. microti of the ‘US’-type in 5·3% of the animals from the Novosibirsk region. Babesia DNA was not detected in 133 analysed I. persulcatus from the Sverdlovsk region; however, it was found in 24 of 789 ticks from the Novosibirsk region. Three distinct Babesia species were detected in I. persulcatus. B. microti ‘US’-type was identified in 10 ticks, Babesia closely related to B. divergens/B. capreoli in 2 ticks, and Babesia closely related to B. venatorum (EU1) in 12 ticks. Conclusion. To our knowledge, this is the first detection of Babesia sensu stricto in I. persulcatus ticks and of B. microti in I. persulcatus in the Asian part of Russia.

Filarial infections of humans are chronic diseases. Despite an ongoing immune response, adult filariae continuously produce their offspring, the microfilariae (Mf), which are able to persist in sufficient numbers to ensure transmission. In this study, host- and parasite-derived factors, which contribute to persistence of Mf, were investigated using the filariasis model of Litomosoides sigmodontis in mice. Different strains of mice were found to differ widely in their capability to eliminate circulating Mf. Studies of congenic mouse strains showed that early and rapid clearance of Mf was mediated by activation pathways relevant to innate immunity, whereas late or delayed clearance of Mf was pre-determined by MHC-related factors. Genetic knock-out of genes for the MHC class-II molecules totally abrogated resistance. Most interestingly, the presence of only 1 adult female, but not male worms, renders all mice susceptible, irrespective of the genetic background, enabling Mf to circulate for extended periods of time. Such prolonged microfilaraemia was also observed in L. sigmodontis-infected animals challenged with heterologous Mf of Acanthocheilonema viteae. The use of cytokine gene knock-out mice showed that persistence of L. sigmodontis Mf was facilitated by IL-10, but not by IL-4 or IFN-γ. In conclusion, irrespective of a resistant or susceptible host genetic background, survival of Mf of L. sigmodontis in mice is decisively regulated by the presence of adult female L. sigmodontis which will skew and exploit immune responses to facilitate the survival and persistence of their offspring in the infected host.

Nine hundred and five brown trout were collected from the River Teify, West Wales, over a period of 12 months and their helminth infestations are considered in relation to the age and sex of the host and season.

Only one statistically significant difference could be detected between levels of infestation in male and female trout of 1 and 2 years of age.

When trout of 3 years of age and over were spawning or recovering from the effects of spawning there is a tendency for sexually mature females to be more heavily infested with some parasites than the males. During the season of growth and maturation of the gonads this trend was reversed or became less marked. In the case of fish that were not spent or spawning the statistically significant differences showed the males to be more heavily infested than the females.

The possible reasons for these variations are discussed with particular reference to the roles of ‘physiological’ and ‘behavioural’ or ecological resistance'.

The behaviour of four species of Eimeria was studied in lambs which were given either monospecific or multispecific infections. In the presence of other species the patency of oocyst production of E. ovina and E. weybridgensis was extended and the total number of oocysts produced by all species except E. ninakohlyakimovae was increased. Clinical symptoms were observed only in lambs which received E. ninakohlyakimovae.