The question of whether the known immunosuppressive effects of Babesia microti may disrupt the development of acquired resistance to its tick vector, Ixodes trianguliceps, in natural rodent hosts (Clethrionomys glareolus), and thus enhance thedisease transmission potential, is addressed experimentally. The results show for the first time that natural hosts can acquire resistance to ticks; that this acquired resistance is manifested chiefly by a strongly density-dependent reduction in the percentage of attached larvae that engorge; that the density dependence is quantitatively similar whether the host receives occasional large tick challenges or frequent low infestations; but that infection with B. microti does not disrupt this pattern of acquired resistance. Of two important natural host species, Apodemus sylvaticus can support repeated infestations of I. trianguliceps, but is a poor host to B. microti, while C. glareolus develops acquired resistance to the tickvector, but supports much higher-level, longer-lasting B. microti infections.

Patterns of nematode fecundity were investigated for infections of the caecal worm Heterakis gallinarum in the ring-necked pheasant (Phasianus colchicus). Worm length was a good predictor of parasite fecundity. After controlling for worm length no other factors, including parasite intensity, were related to worm fecundity. Density dependence in worm size was detected in natural infections at parasite intensities above a threshold of 96 worms (worm size decreased with increasing parasite intensity). However, below this threshold, worm size actually decreased with decreasing parasite intensity (inverse density dependence). The interaction between density dependence and inverse density dependence in regulating the development and subsequent fecundity of H. gallinarum worms in ring-necked pheasants was demonstrated in an infection experiment. Density dependence was observed in the stunted growth of worms in heavily infected hosts, relative to worms in lightly infected hosts. Inverse density dependence in worm size was the common pattern across hosts by the end of the experiment, when parasite intensities were below the density dependence threshold. This is the first study to document both density dependence and inverse density dependence in parasite fecundity in the same host–helminth system.

This paper describes the distribution of Ascaris suum in experimentally and naturally infected pigs, and offers a comparison with A. lumbricoides infections in humans. In the first study, worms were recovered post-mortem from a group of 38 pigs that had been trickle inoculated with 10000 infective A. suum eggs twice weekly for 12 weeks. In the second study, worms were collected from a group of 49 pigs that had been kept on a pasture contaminated with infective A. suum eggs for 10 weeks, after which they received treatment with an anthelmintic; they then were turned out on the same pasture for a second 10-week period before slaughter. The worm burdens of the naturally infected pigs were recorded both at treatment and post-mortem. Mean worm counts were similar at all occasions but the prevalence of infection was higher in the trickle infected and naturally reinfected pigs. Furthermore, the prevalence in naturally infected pigs increased significantly over the study period. Worm burden distributions in all groups were heavily overdispersed, but the distribution patterns differed significantly between groups: lower exposure (initial natural infection) gave a low prevalence and an almost uniform distribution of worm burdens among infected hosts. Continued or higher exposure (trickle and natural reinfection) resulted in increased prevalence and a reduction in the proportion of hosts with increasing worm load. A positive correlation was found between initial and reinfection worm burdens in the naturally infected pig population, suggesting that individual pigs are predisposed to a high or low intensity of infection. The prevalence and intensity as well as the distribution observed for A. suum infection in pigs were comparable to those reported for A. lumbricoides in endemic areas, and there is evidence for predisposition to A. suum in pigs, with an estimated correlation coefficient similar to that found in humans. It is concluded that A. suum infections in pigs are a suitable model to study the population dynamics of A. lumbricoides in human populations.

It is concluded that E. sibiricensis is the etiologic agent of alveolar hydatid disease in man. The cestode has a wide distribution in Eurasia, and St Lawrence Island apparently represents the north-easternmost extent of its range. The study of the cestode in Europe has been complicated by the co-existence of E. granulosus, which does not occur on St Lawrence Island. Microtine rodents, particularly Microtus spp. and Clethrionomys rutilus, are the natural intermediate hosts of this cestode, although other species of mammals, including man, are parasitized with varying degrees of success on the part of the larval cestode.

A holotrichous ciliate found repeatedly in very large numbers in the body cavity of larval midges (Chironomus plumosus) from Paris and Berlin areas is described as a new species of the genus Tetrahymena, named T. chironomi sp.nov. It appears to represent a true example of facultative parasitism, since parasites released from the host survive in laboratory cultures, and free-living ciliates believed identical have been isolated from fresh-water sources in nature. Over a 3-month period more than 2000 larvae, principally fourth-instar stages, were examined; about 9 % of these were found to be infected with ciliates.

T. chironomi is the thirteenth species to be added to the growing holotrich hymenostome genus Tetrahymena. It is taxonomically distinguishable from other members of the genus on the basis of a combination of characteristics related to its morphology and bionomics. It is one of the smallest species, has 24–27 ciliary meridians and a relatively large, spherical micronucleus, does not exhibit dimorphism or cystic stages in its life cycle, and does not possess a caudal cilium.

Prevalence and abundance of Cryptosporodium parvum and Giardia spp. were studied in 3 species of rodents from forests and abandoned agricultural fields in N.E. Poland (Clethrionomys glareolus n = 459; Microtus arvalis n = 274; Apodemus flavicollis n = 209). Overall prevalence was consistently higher in the voles compared with A. flavicollis (70·6, 73·0 and 27·8% respectively for C. parvum and 93·9, 96·3 and 48·3% respectively for Giardia spp.). Prevalence and abundance of infection also varied markedly across 3 years with 1998 being a year of higher prevalence and abundance with both species. Fewer older animals (especially C. glareolus and M. arvalis) carried infection with C. parvum and infections in these animals were relatively milder. Although seasonal differences were significant, no consistent pattern of changes was apparent. Host sex did not influence prevalence or abundance of infection with C. parvum, but made a small contribution to a 4-way interaction (in 5-way ANOVA) with other factors in the case of Giardia spp. The 2 species co-occurred significantly and in animals carrying both parasites there was a highly significant positive correlation between abundance of infection with each, even with between-year, seasonal, host age, sex and species differences taken into account. Quantitative associations were confined to the 2 vole species in the study. These results are discussed in relation to the importance of wild rodents as reservoir hosts and sources of infection for local human communities.

For over 50 years it has been known that there are considerable differences in the severity and rate of progression of both Trypanosoma brucei rhodesiense and T. b. gambiense infection between individuals. Yet research into the factors, whether parasite or host, which control virulence in Human African trypanosomiasis is in its infancy. In this paper we review the clinical evidence for virulence variation and the epidemiological and experimental data that give clues as to the mechanisms involved. Evidence will be presented for both asymptomatic forms of T. b. gambiense infection and low virulence forms of T. b. rhodesiense infection in humans. While in both cases the mechanisms remain to be elucidated, the overall infection virulence phenotype is determined by both parasite and host genotype.

Partial 28S ribosomal RNA (rRNA) gene sequences, including the variable domains D1, D2 and D3, were determined for representative species from the 4 Schistosoma species groups. On an alignment of 1345 bp from S. mansoni, S. haematobium, S. spindale and S. japonicum (with Heterobilharzia americana chosen as an outgroup), both maximum likelihood and maximum parsimony analyses provide a robust molecular phytogeny for the genus; ((((S. haematobium, S. spindale), S. mansoni), S. japonicum), H. americana). When analysed separately, both domain D1 and domain D2 yielded similarly informative data whereas D3 failed to resolve the phylogeny. These results confirm a phylogeny previously suggested by 18S rRNA gene sequences, corroborating the status of S. spindale as a sister taxon to S. haematobium, and demonstrate the utility of 28S rRNA gene sequence data for resolving phylogenies within the Schistosomatidae.

Note: nucleotide sequence data reported in this paper are available in the EMBL database under the accession numbers Z46503/04/05/06/21.

Histological investigations of the bile ducts of various hosts of F. hepatica during the early stages of infection, when the flukes are burrowing in the liver and have not yet reached the bile ducts, indicate that subtle changes are brought about, probably by chemical agencies and as a result of the inflammatory process, in the bile ducts of the hosts. The transitory appearance of minute cytoplasmic blebs at the free margins of the epithelial cells seems to inaugurate an intense hyperplasia of the epithelium with tubular ingrowths and adenomatous development of glandular tissue, and an associated fibrosis which produces a thick underlying layer of dense fibrous tissue. At the time of entry of the flukes into the biliary system the hyperplastic epithelium is intact, but soon the spines and suckers of the flukes abrade the superficial cells until this part of the duct is completely denuded. It is suggested that as a result of the inflammatory reaction, the fluke has been provided with a ‘pasture’ of hyperplastic epithelium and connective tissue on which it may continue to browse for considerable periods without necessarily affecting the host adversely. Tissue debris is found in the contents of the bile duct and similar homogenized materials occur in the caecal contents of the fluke. Previous researches have shown that the fluke will feed on various tissues, and it is suggested that this tissue-feeding habit persists during its life in the bile duct. These results agree with the findings of Müller (1923) but are at variance with the results obtained by other investigators, as is shown in discussion. The hyperplasia of the bile duct is not characteristic of fascioliasis, occurring also in clonorchiasis, opisthorchiasis and dicrocoeliasis, and in these and possibly other instances it is probably intimately connected with the nutrition of the flukes concerned.

Cryptosporidia are important protozoan parasites of vertebrates, and a number of species and genotypes, with different host ranges, have been described. In this study a protocol was established for the detection and the genetic characterization of Cryptosporidium spp. isolated from various types of surface waters (rivers, creeks, lakes, sewage plant in- and outlets and swimming pools) from the area between Zurich (Switzerland) and Munich (Germany). Cryptosporidium oocysts were isolated by continuous-flow-centrifugation and immunomagnetic separation (IMS). A novel nested PCR combined with direct sequencing of the amplicon which spans a variable region of the 18S rRNA allowed characterization of species and genotypes. Cryptosporidium spp. were detected in 23 of the 68 water samples investigated. Almost half of these isolates represent species and genotypes known to be pathogenic to man, namely C. parvum ‘bovine genotype’ (from 6 samples) and C. parvum ‘human genotype’ (4). Furthermore, we identified C. muris ‘genotype A’ (3), C. muris ‘genotype B’ (6), C. baileyi (1) as well as 3 novel Cryptosporidium genotypes. Our results confirm the ubiquitous presence of Cryptosporidium oocysts in surface waters. The detection of a variety of species and genotypes stresses the importance that molecular characterization is indispensable before drawing conclusions of medical or epidemiological significance.

Echinococcus granulosus is the causative agent of cystic echinococcosis. The disease is a significant global public health concern and human infections are most commonly associated with E. granulosus sensu stricto (s. s.) genotype G1. The objectives of this study were to: (i) analyse the genetic variation and phylogeography of E. granulosus s. s. G1 in part of its main distribution range in Europe using 8274 bp of mtDNA; (ii) compare the results with those derived from previously used shorter mtDNA sequences and highlight the major differences. We sequenced a total of 91 E. granulosus s. s. G1 isolates from six different intermediate host species, including humans. The isolates originated from seven countries representing primarily Turkey, Italy and Spain. Few samples were also from Albania, Greece, Romania and from a patient originating from Algeria, but diagnosed in Finland. The analysed 91 sequences were divided into 83 haplotypes, revealing complex phylogeography and high genetic variation of E. granulosus s. s. G1 in Europe, particularly in the high-diversity domestication centre of western Asia. Comparisons with shorter mtDNA datasets revealed that 8274 bp sequences provided significantly higher phylogenetic resolution and thus more power to reveal the genetic relations between different haplotypes.

New ways of integrating and scaling up control of neglected tropical diseases (including schistosomiasis) are presently underway. In this context consideration of social science perspectives is essential. In this article, we review social science publications of relevance to sustained control of schistosomiasis in Africa including diagnosis and screening, treatment, supply of clean water and improved sanitation, as well as health communication. Studies of community involvement and links between schistosomiasis control programmes and broader health care systems are also explored. Directions for future social science of relevance to sustainable schistosomiasis control are outlined, including ways of ensuring equitable access to health services as well as involvement of endemic communities and local health care systems based on equal partnership.

Glugoides intestinalis, Microsporidium sp., Ordospora colligata, Gurleya vavrai, Larssonia obtusa and Flabelliforma magnivora are microsporidian parasites of planctonic freshwater crustaceans Daphnia spp. We performed a phylogenetic analysis of the small subunit ribosomal DNA which revealed their positions as polyphyletic. G. intestinalis, Microsporidium sp. and O. colligata, which are horizontally transmitted gut parasites with small spores and low virulence, group with different lineages. G. intestinalis is related to 2 microsporidia infecting lepidopterans and to Vittaforma corneae, which has been described as a human pathogen. It is thought that V. corneae may have an invertebrate as its natural host. Microsporidium sp. is a relative of the genera Enterocytozoon and Nucleospora, pathogens of man and fish respectively. O. colligata is the first species found to be closely related to the genus Encephalitozoon, which is comprised of 3 species that are parasites of homeothermic vertebrates. G. vavrai and L. obtusa are sister taxa that branch close to the Amblyosporidae, the only microsporidia with known intermediate hosts. This finding supports the presumption of secondary hosts for G. vavrai and L. obtusa, as it has not been possible to maintain these species in Daphnia in the laboratory. F. magnivora roots deep at the base of the phylum microsporidia with no close relative found so far.

Using microelectrode structures, various forms of electric fields, such as non-uniform, rotating and travelling wave, can be imposed on particles of sizes ranging from proteins and viruses to micro-organisms and cells. Each type of particle responds to the forces exerted on them in a unique way, allowing for their controlled and selective manipulation as well as their characterization. Moreover, particles of the same type but of different viability can be distinguished in a simple, reliable manner. This review outlines the principles that govern the way in which bioparticles respond to these various field types, and how they can be exploited. Examples of current and potential biotechnological and biomedical applications are given, along with a critical comparison of current techniques.

The species Echinococcus granulosus is made up of several genotypic strain groups, whose taxonomical classification is still undetermined. Genotypes in the cervid-wolf life-cycle are poorly known, especially in Europe. In this study, 33 Echinococcus isolates from cervids from Finland and Sweden were characterized using mitochondrial ND1 gene sequencing. In addition, phylogenetic analysis of E. granulosus strains using the mitochondrial ATP6, ND1, ND3 and CO1 genes was performed using maximum likelihood, neighbour-joining and maximum parsimony methods. The Finnish and Swedish cervid isolates were found to represent the genotype G10. In the phylogenetic analyses, the camel (G6), pig (G7), cervid (G8) and Fennoscandian cervid (G10) strains clustered in a well-supported monophyletic group. This group differed clearly from the common sheep (G1) and horse (G4, ‘E. equinus’) strains, but was closely related to the cattle strain (G5, ‘E. ortleppi’). Our results support the previous studies suggesting that the genotypes G6-10 should be separated from the species E. granulosus sensu stricto. However, additional morphological studies are needed, and the relationship to the cattle strain (‘E. ortleppi’) should be thoroughly evaluated before a final decision of the taxonomical status of the G6-10 group can be made.

Ixodes ricinus horizontal movement within a humidity gradient and the influence of infection by Borrelia burgdorferi sensu lato (s.l.) on tick walking were investigated. Nymphs were placed within an arena containing a humidity gradient ranging from 45 to 95% relative humidity (RH). After 1 h of acclimation at 70% RH ticks were released so that they could either stay, or walk towards either the wet or the dry end. Their position was recorded 2 h post-release. Fat content was quantified and Borrelia infection was detected using real-time PCR and PCR followed by Reverse Line Blotting. Among the 1500 ticks tested, 29·85% were infected. More low-fat nymphs walked inside the arena than high-fat individuals. When nymphs walked, more low-fat ticks walked towards wetter than drier air, whereas more high-fat individuals walked towards drier than wetter air. Among high-fat nymphs, a lower proportion of Borrelia-infected ticks walked inside the arena compared to uninfected individuals, as though spirochetes manipulated their arthropod vector to stay. However, Borrelia infection had no effect on walking direction towards the dry or the wet end. Hence, it appears that I. ricinus nymphs walk horizontally over short distances within a humidity gradient depending on both energy resources and Borrelia infection.

A benznidazole-resistant population of Trypanosoma cruzi, Y strain, was selected after 25 successive passages (8 months) in mice treated with a single high drug dose. Initially, the resistant parasites produced a low parasitaemia level and low mortality rate in infected mice. Thereafter, the parasitaemia level and mortality rate increased to the same value obtained for mice infected with the wild-type strain. Long-term treatment with benznidazole (100 mg/kg/day) cured 71–80% of mice infected with the wild-type strain. No cure was observed in mice infected with the selected resistant parasite population. Treatment with 500 mg/kg of benznidazole at peak parasitaemia cleared all blood parasites from mice infected with wild-type parasites. No effect on parasitaemia level was observed in mice infected with the selected parasites. Benznidazole-resistant parasites showed cross-resistance to different drugs. Contrary to wild type, all clones analysed from the resistant T. cruzi population were resistant to benznidazole. Without drug pressure the resistance phenotype of clones was far more stable than that presented by the resistant population. This work demonstrates, for the first time, the in vivo selection of a population and clones of T. cruzi resistant to benznidazole, and makes available an experimental model for the study of mechanisms of drug resistance in T. cruzi.

Lung-stage schistosomula are the target of protective immunity in mice vaccinated with attenuated cercariae of Schistosoma mansoni. Therefore, proteins present at this developmental stage, and in particular those which are secreted, are a potential source of novel vaccine candidates. However, little information is available about such molecules. Here we describe the cDNA clones identified by screening expression libraries with serum raised against proteins released by lung-stage schistosomula. In total, 11 different cDNA species were identified, 6 of which have been described previously in S. mansoni; these included fructose 1,6-bisphosphate aldolase and Sm21.7 which together accounted for two-thirds of all positive clones. Of the 5 newly described schistosome genes, 1 cDNA had a high degree of homology to the s5a subunit of 26S proteasomes, most significant being with the human protein. The remaining 4 clones showed no significant homologies to any genes sequenced previously. Fructose 1,6-bisphosphate aldolase, Sm21.7, the proteasome homologue and 1 unknown clone (A26) have been expressed in a bacterial expression system and serum produced against each recombinant protein. Immunolocalization showed fructose 1,6-bisphosphate aldolase, Sm21.7 and the proteasome homologue to be most abundant in muscle cells whilst clone A26 was distributed throughout many tissues, but was most abundant in the tegument. Analysis of the cellular immune responses of vaccinated mice showed 3 of the 4 expressed clones to be highly immunogenic, inducing the secretion of large quantities of the Th1-type cytokine interferon gamma.

Acquired immunity to Schistosoma mansoni in the rat can be assayed by the recovery of a proportion of the schistosomula of a challenge infection from the lungs 5 days after the challenge has been given. The recoveries from immune rats, which are significantly less than those from control animals, demonstrate that a proportion of a challenge infection is killed in the lungs or at an earlier point in the pathway of migration.

Immunity in the Sprague–Dawley rat can first be shown by the lung recovery technique 3 weeks after an immunizing exposure of 500 cercariae. Immunity reaches a peak between weeks 6 and 7 but then declines to zero by week 12. The PVG inbred Hooded rat shows a similar but delayed development and decline of immunity. When the lung recovery technique shows immunity to be declining, hepatic perfusion demonstrates that immunity to reinfection is partially retained, indicating that at this stage the challenge is killed after the first 5 days.

Re-exposure of rats in which immunity has declined induces an anamnestic lung recovery response. There appears to be a relationship between spontaneous cure and the decline of immunity. A factor in the serum of infected rats which kills young schistosomula in culture develops in parallel with immunity, but high titres of this factor are maintained during the decline of immunity.

The chemical and physical nature of monogenean attachment sclerites has been investigated by chromatography, histochemistry, solubility studies and X-ray diffraction, and these sclerites have been shown to be scleroproteinaceous and not, as the bulk of the literature suggests, chitinous in composition.

Hooks sclerites (i.e. marginal hooks and hamuli), which are the most primitive type of monogenean attachment sclerites and arise early on ontogeny, have been shown to be keratinous; clamp sclerites, accessory bars and the spines arming the pseudohaptors and squamodisks of certain genera which appear to have been acquired later in the phylogeny of the group to supplement the efficiency of the haptoral hooks, contain no cystine sulphur.

While the chemical nature of the non-cystine-containing skeletal structures has not been fully elucidated, clamp substance was found to differ from that of the other scleroproteins with which it was compared, namely sclerotin, vertebrate elastin, reticulin, collagen and keratin. Clamp substance does not appear to be quinonetanned; acid proteins maybe important in the stabilization of this scleroprotein.

Evidence for the occurrence of a variety of S–S bearing scleroproteins throughout the invertebrates has been collated and the problems involved in adequately defining a keratin have been discussed. The implications of the apparent affinity of monogenean hook protein to vertebrate keratins, which in general are intracellular and epidermal derivatives have been considered and some speculations have been made about the possible differences in the development of hook and clamp structures.

Contrary to the prevalent opinion that monogenean sclerites are ‘cuticularizations’, evidence has been presented that these structures are in fact deeply seated and unlikely to be derivations of a superficial cuticle.

The chemical differences elucidated between the median and lateral sclerites of the chimaericolid adhesive organ have encouraged speculation on the evolution of the different types of attachment organ throughout the polyopisthocotylineans.

Outside the Monogenea, studies on the sulphur content of digenean spines and stylets and on the larval hooklets of the ‘cestodarians’ Gyrocotyle, Amphilina and Archigetes, and of eucestodes, have helped to substantiate the view that the cestodes and monogeneans are more closely related to each other than either of these groups is related to the digeneans.

I wish to thank the Director and staff of the Plymouth Laboratory and in particular Mr J. E. Green, for invaluable assistance. I am also indebted to Dr R. W. H. Small for his guidance on X-ray diffraction technique, to Dr J. Morris of the M.R.C. Skin Unit for his advice on the chromatography and to Dr J. Llewellyn for his interest and helpful criticism throughout.