Parasite transmission dynamics are fundamental to explaining the evolutionary epidemiology of disease because transmission and virulence are tightly linked. Horizontal transmission of microsporidian parasites, e.g. Nosema bombi, may be influenced by numerous factors, including inoculation dose, host susceptibility and host population heterogeneity. Despite previous studies of N. bombi and its bumble bee hosts, neither the epidemiology nor impact of the parasite are as yet understood. Here we investigate the influence N. bombi spore dosage (1000 to 500 000 spores), spore source (Bombus terrestris and B. lucorum isolates) and host age (2- and 10-day-old bees) have on disease establishment and the presence of patent infections in adult bumble bees. Two-day-old bees were twice as susceptible as their 10-day-old sisters, and a 5-fold increase in dosage from 100 000 to 500 000 spores resulted in a 20-fold increase in the prevalence of patent infections. While intraspecific inoculations were 3 times more likely to result in non-patent infections there was no such effect on the development of patent infections. These results suggest that host-age and dose are likely to play a role in N. bombi's evolutionary epidemiology. The relatively low levels of horizontal transmission success are suggestive of low virulence in this system.

Despite years of investigation into triclabendazole (TCBZ) resistance in Fasciola hepatica, the genetic mechanisms responsible remain unknown. Extensive analysis of multiple triclabendazole-susceptible and -resistant isolates using a combination of experimental in vivo and in vitro approaches has been carried out, yet few, if any, genes have been demonstrated experimentally to be associated with resistance phenotypes in the field. In this review we summarize the current understanding of TCBZ resistance from the approaches employed to date. We report the current genomic and genetic resources for F. hepatica that are available to facilitate novel functional genomics and genetic experiments for this parasite in the future. Finally, we describe our own non-biased approach to mapping the major genetic loci involved in conferring TCBZ resistance in F. hepatica.

We present an analysis of the survival and migration rates of the infective (L3) stages of Oslertagia ostertagi and Cooperia oncophora. Although the majority of laboratory studies show that the survival of the L3 stage depends upon temperature, moisture and the age of the larvae, a simple mathematical model of larval demography, in which their mortality and migration rates are held constant, provides as good agreement between observed and predicted larval counts as models in which these rate processes are made explicit functions of larval age and microclimate. Maximum-likelihood estimates of larval mortality rates in the faeces and on the herbage are 0·0284/day and 0·00887/day respectively. The average migration rate from faeces to herbage under temperate Northern European conditions is estimated as 0·00884/day. Finally, we discuss the probable scale of L3 larval losses due to desiccation and lavage (active or passsive migration into the soil).

A cDNA encoding a cysteine protease inhibitor (cystatin) was identified by immunoscreening a Haemonchus contortus cDNA library with antisera from lambs vaccinated with a protective membrane protein complex (H-gal-GP) derived from the gut of the parasite. The cDNA sequence, designated Cys-1, showed significant levels of similarity with cystatins from several species of nematode as well as with human cystatinNucleotide and amino acid sequence data reported in this paper are available in the GenBankTM database under the accession number AF035945.. Recombinant H. contortus cystatin was expressed in Escherichia coli in a soluble and functionally active form, which proved to be a potent inhibitor of both mammalian cathepsin B and native H. contortus cysteine proteases. Immunolocalization studies using antisera raised against recombinant H. contortus cystatin showed that the inhibitor was predominantly expressed in the cytoplasm of intestinal cells. To determine whether H. contortus had any protective capacity against infection, lambs were vaccinated with the recombinant molecule and subsequently given a single challenge infection. Although vaccination did not confer any protection against infection with H. contortus, as judged by faecal egg output or worm counts, cystatin will be a valuable tool in the analysis of the function of the cysteine proteases which are the subject of on-going study as potential vaccine components.

The protein composition of Schistosoma mansoni was analysed by electrophoresis in polyacrylamide slab gels in the presence of sodium dodecyl sulphate. A high degree of identity existed between protein patterns obtained from immature and adult parasites of the two sexes. Some stage-and sex-specific components were identified and their possible origin discussed.

The pre-feeding and feeding periods of larvae, nymphs and adults of Rhipicephalus appendiculatus on rabbits (Oryctolagus cuniculus) were investigated. Larvae and nymphs required at least 8–9 days after hatching and moulting respectively before they could attach and start feeding, while adults required at least 6–9 days. But longer periods of starvation improved the proportion of ticks that successfully fed.

After attachment, there was always an initial period of slow feeding, which was followed by a phase of very rapid feeding before the engorged ticks detached from the host. Larvae detached 4–5 days after attachment, nymphs detached after 5–6 days and adults detached 7–9 days after attachment.

In order to construct an analytical model of onchocerciasis transmission, it is necessary to elucidate the functional relationships of the various population rate processes taking place within the human and vector hosts. Two previous papers have explored the evidence for density-dependent regulation in relation to microfilarial intake by, and larval development within, the Simulium host. This paper investigates the survivorship of wild-caught blackfly samples fed on subjects with different intensities of Onchocerca volvulus microfilarial infection. Analyses were based on data for Guatemalan S. ochraceum s.l. (possessing a well-developed cibarial armature), West African S. damnosum s.l. (forest species), and South Venezuelan S. guianense (the latter two lacking a toothed cibarium). The mean survival times of samples of the 3 species, kept under laboratory conditions, decreased as parasite intake increased, the rate of mortality being dependent on the fly’s age (measured as time post-feeding) and on the worm load acquired. An empirical, timedependent hazard function was fitted to observed death rates/fly/day which rose very shortly after engorgement, declined subsequently, and rose again throughout the extrinsic incubation period of the parasite. The parameters of this hazard model were all positively correlated with the density of microfilariae in the bloodmeal. Expressions of survivorship and life-expectancy as explicit functions of time post-feeding and mean parasite intake were derived. The average expectation of life at engorgement for uninfected flies in the laboratory was estimated to be around 1 week for both, armed and unarmed blackflies. Residual life-expectancy decreased with time post-feeding and microfilarial load in both categories of vectors. This decline (resulting from age- and parasite-dependent mortality rates) was much more pronounced in those species lacking a toothed fore-gut. Whilst a fraction of heavily infected S. ochraceum was able to survive the latent period of the parasite, being therefore potentially capable of transmitting the infection, equivalent worm loads in S. guianense resulted in a drastic reduction of the expectation of infective life. These results provide additional evidence to support the hypothesis that, in the case of intrinsically susceptible vectors, unarmed simuliids are more efficient at low microfilarial loads, when the transmission rate from human to vector host is higher, and parasite-induced fly mortality is negligible. The opposite takes place in armed flies, which perform poorly at low parasite burdens and better at heavier loads, with little parasite-induced vector death.

The more important points that have emerged in the course of our investigations may now be assembled.

(1) An adhesion phenomenon has been described in which, in certain circumstances, red blood corpuscles adhere to trypanosomes.

(2) We believe this red-cell adhesion to be a manifestation of the adhesion phenomenon already described by other workers both with trypanosomes and spirochaetes.

(3) The substance responsible for this phenomenon of adhesion is designated in this paper adhesin.

(4) The red-cell adhesion test has been studied in relation to several strains of polymorphic trypanosomes, all of which were either recently isolated from naturally infected man or animals, or had been recently passed cyclically through tsetse.

(5) It is shown that the adhesion phenomenon is irregular and uncertain in its appearance. A single or even a number of negative observations do not exclude trypanosomiasis. A positive reaction, on the other hand, indicates recent or actual infection with a trypanosome of the same group, but not necessarily specifically identical with that employed as antigen in the test. Thus T. gambiense adhesin bloods not uncommonly react with T. rhodesiense trypanosomes and also on occasion with the Damba strain: the converse is apparently of less common occurrence.

(6) Adhesins appear in an animal's blood in the course of its infection with trypanosomes, whether the animal be treated with trypanocidal drugs or not. When sterilising doses of such drugs are employed the adhesins gradually disappear in the course of a few months; but in untreated infections of T. gambiense they have been shown to persist in an active form for more than two years.

(7) With our material it was found impossible to distinguish between “passage” and “relapse” strains by means of the adhesion test. On the contrary it was found, at all events with T. gambiense, that the best way to call forth the reaction in the blood of animals long infected is to employ trypanosomes from a very early infection.

(8) Guinea-pigs have been found to be unsatisfactory animals in which to demonstrate adhesins; they are, however, useful as a source of sensitive trypanosomes. When only guinea-pig elements are present in a test a positive reaction is indicated by platelet not by red-cell adhesion.

(9) The presence of adhesins in the blood has no apparent relation to immunity against the homologous trypanosome.

(10) The test has been applied to over 200 human cases of trypanosomiasis in the Uganda Protectorate, and with six of these repeated observations were made. Some of these human cases reacted both to T. gambiense and T. rhodesiense, but none to T. rhodesiense alone.

(11) A partial analysis has been made of the mechanism of red-cell adhesion, which has been shown to be in some way associated with the presence of the red corpuscles of primates. This fact probably explains why other workers appear not to have noticed red-cell adhesion in the extreme form we have described in this paper.

The aim of this study was to construct risk maps for the presence of the dominant Leishmania infantum vector, P. perniciosus, and check its usefulness (a) to predict the risk of canine leishmaniasis and (b) to define effective leishmaniasis control measures. We obtained data for the presence/absence of P. perniciosus at 167 sampling sites in southern Spain, from which we also took a series of ecological and climate-related data. The probability of P. perniciosus presence was estimated as a function of these environmental variables and generated spatial risk maps. Altitude, land use and drainage hole features (with or without PVC piping) were retained as the only predictors for the distribution of this vector species. Drainage hole features in retaining walls, with or without PVC piping, produce significant variations in the probability of P. perniciosus presence, varying from 2·3 to 91·8% if PVC piping is absent and from 0·4 to 66·5% if all holes have PVC piping. It was concluded that the use of PVC piping in drainage holes could help to reduce leishmaniasis transmission.

Infection of an intracellular parasitic nematode, Trichinella spiralis, resulted in severe damage in muscle cells which was followed by activation and proliferation of satellite cells. The repairing process, shortly after the damage, histopathologically resembled those seen after mechanical injury. Resemblance was also true for kinetics of expression of myogenic regulatory factors (MyoD, myogenin and MRF4). The difference resided in the next step where the muscle cell infected with T. spiralis transformed to a unique cell which is parasitologically known as the nurse cell, and the proliferated satellite cells did not differentiate to the muscle cell but to the nurse cell (misdifferentiation). Thus the nurse cell was a fusion of the transformed infected muscle cell and misdifferentiated satellite cells. Infection with another species of Trichinella, T. pseudospiralis, also caused cell damage, but more extensively involving the entire length of the infected muscle cells because no septum was formed to minimize the affected area. Therefore, a large number of satellite cells were activated and proliferated. The myogenic regulatory factors such as MyoD and myogenin were activated for a longer period than in the case with T. spiralis infection. The infected muscle cell transformed to the nurse cell, whose cytoplasm was characterized by extensive smooth endoplasmic reticulum. Satellite cells misdifferentiated to the nurse cell, whose cytoplasm was amorphous, void of distinct cell organelles. The two kinds of cytoplasm did not fuse as examined thus far. Thus infection with T. spiralis and T. pseudospiralis caused misdifferentiation of satellite cells, but in a different way.

To assess the potential role of IgA antibody in expulsion of the nematode of the genus Trichinella from the intestine, a panel of IgA monoclonal antibodies (mAbs) were produced from the mesenteric lymph node cells from BALB/c mice orally vaccinated with irradiated muscle larvae of Trichinella britovi. One IgA mAb, HUSM-Tb1, formed immunoprecipitates on the surface of live muscle larvae, and by immunohistochemistry reacted with their stichocytes and cuticular surface, but not with those tissues of the adult stage or newborn larvae. Intraperitoneal injection of BALB/c mice with this mAb 5 h before challenge conferred a high level of protection (more than 95%) against T. britovi infection, when 2·0 mg of specific IgA/20 g body weight was given to a mouse. The same treatment produced a similar effect in SCID mice lacking functional T- and B-cells, indicating no requirement of synergistc T-cell factors for the effect. Passive transfer of the mAb at the time of challenge or later showed less or no effect upon worm expulsion. It is concluded that the mucosal IgA response, when adequately induced, can impede the establishment of infective Trichinella parasites in the mouse intestine.

A dilution medium for the cultivation in vitro of the erythrocytic stages of P. knowlesi has been simplified to contain the following: a balanced salt solution, glucose, isoleucine, methionine, adenosine, p-aminobenzoic acid, biotin and calcium pantothenate. The medium, in the presence of plasma gave better results than the Harvard medium for the growth of P. knowlesi during one asexual cycle and also allowed the subculture of the parasites through three asexual cycles before a reduction in the number of parasites was observed.

We should like to thank Dr F. Hawking and Dr K. N. Brown for their advice and Mr T. J. Scott-Finnigan for technical assistance. One of us (P.I.T.) received financial assistance from the World Health Organization.

Plants containing condensed tannins (CT) may have potential to control gastrointestinal nematodes (GIN) of cattle. The aim was to investigate the anthelmintic activities of four flavan-3-ols, two galloyl derivatives and 14 purified CT fractions, and to define which structural features of CT determine the anti-parasitic effects against the main cattle nematodes. We used in vitro tests targeting L1 larvae (feeding inhibition assay) and adults (motility assay) of Ostertagia ostertagi and Cooperia oncophora. In the larval feeding inhibition assay, O. ostertagi L1 were significantly more susceptible to all CT fractions than C. oncophora L1. The mean degree of polymerization of CT (i.e. average size) was the most important structural parameter: large CT reduced larval feeding more than small CT. The flavan-3-ols of prodelphinidin (PD)-type tannins had a stronger negative influence on parasite activity than the stereochemistry, i.e. cis- vs trans-configurations, or the presence of a gallate group. In contrast, for C. oncophora high reductions in the motility of larvae and adult worms were strongly related with a higher percentage of PDs within the CT fractions while there was no effect of size. Overall, the size and the percentage of PDs within CT seemed to be the most important parameters that influence anti-parasitic activity.

Ascaris suum and Ascaris lumbricoides exhibit an over-dispersed frequency distribution in their host populations in both the adult and larval stages. The impact of host factors on this observed distribution is still poorly understood and difficult to investigate in the natural host populations. The use of a mouse model has been supported by the observations that the larval migratory pattern, in this host, mimics the pattern observed in the pig. We explored the extrinsic factors that might affect the quantitative recovery of larvae during this migration in order to standardize a model system facilitating accurate future assessment of host genetic variation on this phase of the infection. In Exp. 1 larvae accumulated in the livers of both C57BL/6j and BALB/c mice up to and including days 4–5 p.i. and then declined in both strains until day 9. Loss of larvae from the livers corresponded to arrival in the lungs and maximum accumulation on day 7 p.i. but recovery was considerably higher in C57BL/6j mice. It was concluded that day 7 recoveries gave the best indication of relative resistance/susceptibility to this parasite. In Exp. 2 A/J, BALB/c, CBA/Ca, C57BL/6j, C3H/HeN, DBA/2, NIH, SJL, and SWR mice were compared. C57BL/6j mice were identified as the most susceptible strain and CBA/Ca mice as having the most contrasting phenotype, but with a similar kinetic pattern of migration. Finally, in Exp. 3, a strong positive correlation between the size of the inoculum and the mean worm recovery from the lungs was found in CBA/Ca and C57BL/6j mice, but the difference between these strains was highly consistent, 66·6–80%, regardless of the initial dose. These results demonstrate that, using our protocols for infection and recovery, between-experiment variation in A. suum worm burdens is minimal, and that C57BL/6j mice are highly susceptible to infection compared to other strains. The mechanistic basis of this susceptibility in relation to the resistance of other strains is unknown, but the possibilities are reviewed.

The structure of helminth communities in wild rodents is subject to seasonal variation, and is dependent on host age within years. Although between-year variation has been monitored, seldom has it been assessed rigorously by appropriate multifactorial analysis with potentially confounding factors taken into account. In this study we tested the null hypothesis that despite seasonal, host age and sex effects, helminth communities should show relative stability between years. Over a period of 3 years (1998–2000) we sampled bank vole (Clethrionomys glareolus) populations (total n=250) at 2 points in the year: in spring, at the start of the breeding season, and in autumn, after the cessation of breeding. In spite of seasonal differences and strong age effects, the between-year effects were surprisingly small. Measures of component community structure (Berger-Parker dominance index, the dominant species, S. petrusewiczi) did not vary, or varied only slightly from year to year. The majority of measures of infracommunity structure [Brillouin's index of diversity, prevalence of all helminths combined, prevalence and abundance of H. mixtum (the most prevalent helminth), mean species richness] did not differ significantly between years when other factors such as age, sex and seasonal variation had been taken into account. Some between-year variations were found (at the component community level, Simpson's index of diversity; at the infracommunity level, prevalence and abundance of S. petrusewiczi and abundance of all helminths combined), but even these were modest in comparison to seasonal and age differences, and were primarily attributable to S. petrusewiczi. We conclude that despite dynamic within-year fluctuations, helminth communities in bank voles in this region of Poland show relative stability across years. The sporadic occurrence of individual platyhelminths at low prevalence, makes little difference to the overall structure, which is largely maintained by the key roles played by the dominant intestinal nematodes of bank voles and the rarer species collectively.

Timely diagnosis of the nematode Angiostrongylus vasorum in dogs is important in view of severe and permanent lung and cardiovascular lesions that may occur. The performance of the classical Baermann coprological method was compared with ELISAs for the serological detection of circulating antigen and specific antibodies and with Polymerase chain reaction (PCR) performed on EDTA blood, feces and tracheal swabs of serial samples from experimentally inoculated dogs over 13 weeks post inoculation (wpi) (n = 16) and following anthelmintic treatment (n = 6). Patency was observed from 6·7 to 7·6 wpi in all dogs, Baermann results were then mostly positive (116/119, 97%) during the patent period, with wide variations in the numbers of first stage larvae numbers. Blood PCR was tested positive on 1–2 occasions in 11/16 dogs in the pre-patent period, while all tested positive by antibody-detection ELISA by 6 wpi. The proportion of dogs testing positive by fecal PCR and antigen-detection ELISA rose early in the patent period. Tracheal swabs were occasionally DNA-positive in 3/16 dogs starting from 10 wpi. Following treatment, larval excretion stopped within 3 weeks and blood PCR results became negative within 1 week (5/6 dogs), while 4/6 dogs were positive for parasite DNA in tracheal swabs. Parasite antigen and specific antibodies both persisted in the blood for 3–9 weeks after treatment, with average optical densities and the proportion of positive dogs falling gradually, while results using other tests were much more variable. Results indicate that the earliest and most consistent results are obtained by the ELISAs, which can also be used for monitoring dogs after anthelmintic treatment.

Immunity to the adult stage of Trichinella spiralis, assessed by an acceleration of worm expulsion, was transferred to recipient mice with mesenteric lymph node cells (MLNC) or serum taken from infected donors. Immunity was transferred most effectively by MLNC taken from donors infected for 8 days, i.e. donors actively responding to infection. Transfer of both MLNC and serum brought about a marked acceleration of worm expulsion in all cases, even where MLNC or serum given separately failed to transfer a significant degree of immunity.

The number of cercariae of Transversotrema patialense which attach to the fish host Brachydanio rerio, during a fixed exposure period, is shown to be directly proportional to cercarial density within an experimental infection arena. The distribution of successful infections/host is shown to change from a random pattern to an over-dispersed form as cercarial exposure density or duration of host exposure to infection increases. A stochastic simulation model is used to demonstrate that small differences in host susceptibility to infection, within a population of hosts, can generate patterns of dispersion in parasite numbers/host similar to those observed in the experimental studies. Differences in host behaviour, during the period of exposure to infection, are thought to generate variability in host susceptibility to cercarial infection.

Sex steroids play a significant role in regulating the parasite load in experimental intraperitoneal Taenia crassiceps cysticercosis of male and female Balbc/anN mice. Briefly, oestrogens increase parasite loads and androgens decrease them (1) by acting directly on the parasite, favouring or hindering its reproduction, respectively, and (2) by biasing the hosts' immune response towards a parasite-permissive Th2 or a parasite-restrictive Th1 response. The infected male host also undergoes drastic endocrinological and behavioural changes that may impinge upon the course of infection, and the host's mating behaviour and its exposure to predators. In addition, at different times of infection, significant changes occur in the expression of c-fos in the host's hyppocampus, hypothalamus and preoptic area. Thus, the host's brain seems to sense and/or react to intraperitoneal infection. The physiological domains of the network affected by the infection, which classically included the hypothalamus-pituitary-axis and the immune system, must now incorporate the host's sexual hormones and other areas of the brain. The network's complex circuitry and functions may help understand some basic questions of parasitology (i.e. the hosts' sexual dimorphism in parasite infections, host-parasite specificity, heterogeneity in the course and outcome of infections at different stages of parasite and host development). The plurality of elements and the complexity of the network that regulates the host-parasite relationship also point to additional strategies for the treatment and control of infections.

Although clam populations in France are known to be infected with protozoans of the genus Perkinsus, no molecular characterization was previously performed on these parasites. Considering that several members of this genus have been associated with mortalities of molluscs worldwide, a study was undertaken in order to characterize these parasites in France. For that purpose, clams, Ruditapes philippinarum and R. decussatus, collected from different production areas and found to be infected with Perkinsus sp. in thioglycolate culture medium, were selected for PCR-RFLP tests and sequencing. Perkinsus olseni was detected in all the investigated areas and results also suggested the presence of P. chesapeaki in Leucate, a lagoon on the Mediterranean coast and in Bonne Anse in Charente Maritime, on the Atlantic coast. Clonal cultures from both detected species were produced in order to describe and compare in vitro stages. Differences in size between both Perkinsus spp. were noticed especially for schizonts and zoosporangia. Lastly, in situ hybridization tests allowed confirmation of the presence of both species in the same R. decussatus population and even in same clams. This is the first detection of P. chesapeaki in Ruditapes species and outside North America, which questions its introduction into Europe.