We have determined the molar content of guanine + cytosine (GC content) of DNA of the filarial nematode (Brugia malayi, Brugia pahangi and Dirofilaria imitis) and of the free-living soil nematodes Caenorhabditis elegans and have analysed the DNA for the presence of methylcytosine. Two independent methods, thermal denaturation and direct analysis of base content by HPLC following enzymatic hydrolysis, reveal that the GC content of filarial nematodes is 26–28%. We have been unable to find methylcytosine in the DNA of B. malayi.

A FMRFamide-like peptide has been detected in the nematode Ascaris suum, using the peroxidase-anti-peroxidase (PAP) immunocytochemical technique. Positive reactions were obtained in both the central nervous system and the peripheral nervous system of the worm, the strongest reactions being in the anterior nerve ring, the cephalic papillary ganglia, the lateral ganglia and the dorso-rectal ganglion. Immunoreactivity was observed along the length of the main nerve cords of the worm and, to a lesser extent, in the pharyngeal nerve cords. The possible role of this neuropeptide in the physiology of the nematode is discussed.

Several recent studies have demonstrated predisposition of certain humans to heavy gastro-intestinal nematode infections. This finding has been used to support the concept of community control of nematodes based on selective treatment of the few heavily infected individuals in the community. A mouse model has been used in this study to determine whether those individuals found to be ‘predisposed’ to heavy infection continue to regain heavy nematode infections following repeated anthelmintic treatments. Re-infection was examined over 3 intervals of 8 weeks in 52 mice and individual worm burdens attained following drug-induced expulsion were analysed. In the case of Heligmosomoides polygyrus, parasite numbers obtained after first treatment were only significantly correlated with those obtained after the second treatment. Re-infection levels in mice during the second and third re-infection periods did not correlate with parasite loads at the beginning of the study. In the case of Aspiculuris tetraptera, correlations after each re-infection period remained significant, although the magnitude of the correlation coefficient decreased with successive re-infection intervals. The data suggest that a selective control programme based on repeated screening to identify heavily infected individuals prior to each treatment would reduce the number of H. polygyrus in the host population 17–6% more than a single screening at the beginning of the control programme, and would reduce the number of A. tetraptera by 14% more than a single screening. Re-infection rates for H. polygyrus were shown to decrease with increasing mouse age whereas re-infection rates for A. tetraptera increased with increasing mouse age.

In Trypanosome congolense, the surface antigens expressed by cultured metacyclic forms are a limited and serodeme-specific subset of variable antigen types (VATs). Experiments were carried out in mammalian-form (MF) cultures, comprising dividing trypanosomes which express metacyclic VATs (M-VATs) maintained in vitro with a mammalian cell feeder layer, or in mice following infection with cultured metacyclic populations. Selective neutralization experiments were performed by incubating populations of trypanosomes with one or a combination of McAbs to remove their respective M-VATs. Deletion of one M-VAT from the population had no effect on expression and growth of other unrelated M-VATs. Deleted M-VATs were detected in very small proportions of the total population 2–7 days following neutralization. Subsequent incubation of neutralized cultures resulted in growth of deleted M-VATs which, in most cases, reached pre-neutralization levels. It appears, therefore, that in conditions where expression of M-VATs on dividing trypanosomes occurs, removal of individual M-VATs results in their re-expression within the population.

Passive transfer experiments showed that 76% of the resistance induced in CBA/Ca mice by exposure to radiation-attenuated cercariae of Schistosoma mansoni could be transferred to naive recipients by administration of donor serum. The level of protection achieved depended on the volume of serum administered and immunity was demonstrated most consistently with serum harvested from thrice vaccinated donors. The serum was twice as effective when given to the recipients at the time of cercarial challenge as compared to administration 5 days after challenge, a result which indicates that serum-dependent challenge elimination is probably accomplished in the cutaneous tissues. This view was confirmed by the observation that passive protection could be ablated by administration of a monoclonal antibody which we have shown elsewhere to deplete the cutaneous inflammatory reaction to cercarial penetration. Histopathological studies revealed that vaccine serum induced subdermal inflammatory reactions in challenged recipient mice which were identical both in induration and kinetics to those seen in conventionally vaccinated individuals; on days 4 and 5 post-challenge, the reactions comprised 60% mononuclear cells and 40% eosinophils. Challenge larvae, which had transformed from skin-stage to lung-stage parasites, became trapped within such reactions and eventually showed generalized vacuolation consistent with the onset of damage. Some foci were seen to contain degenerated leucocytes, free eosinophil granules and debris which is thought to represent the remnants of dead parasites. Small focal reactions were identified on occasion in naive challenged mice and in recipients of normal mouse serum, but these reactions comprised predominantly mononuclear cells and were rarely seen to encompass challenge parasites. These data show that serum-transferred resistance in the vaccinated CBA/Ca mouse model involves the induction of a cutaneous inflammatory response in the recipients.

The ultrastructure of the formation of the first-stage cuticle within the egg of Trichostrongylus colubriformis is described. The first indication of cuticle formation was the formation of the epicuticle external to the epidermal plasma membrane. This becomes thickened to form the epicuticle of the fully formed cuticle. Microtubules and microfilaments associated with the epidermal plasma membrane were observed during the early phases of cuticle formation. The basal zone was secreted into the space between the epicuticle and the epidermal plasma membrane, followed by the formation of the cortical zone. The basal zone had a striated appearance during the earliest stages of its formation.

The course of primary and secondary infections with Trichostrongylus tenuis in the domestic chicken was investigated. Primary infections were established after the administration of single and trickle doses of infective-stage larvae. The worm burden in the caeca was highest after a single dose of 500 infective-stage larvae; this gave a mean of 87 nematodes per bird on days 8–9 of infection, 20 nematodes on day 14 and 0 on day 28 of infection. Following trickle doses of 60, 100, 200, 300, 400 or 500 infective-stage larvae, there was a rise and then a fall in nematode egg output in all groups. In chickens given a primary dose of 500 infective-stage larvae followed 30 days later by a single secondary dose of 500 infective-stage larvae, the mean worm burden during the secondary infection rose to 57 nematodes on day 9 of infection and then fell rapidly to 18 nematodes on day 15 and to 2 on day 30. Scanning electron microscopy showed changes in the caeca of infected birds, with the caecal surface being covered in a layer of mucus from 12 days after infection. Balls of blood-stained mucus containing nematodes were observed in the caecal droppings from day 9 of infection onwards. It is concluded that chickens rapidly expel an established infection of T. tenuis, unlike the normal host, the red grouse.

The techniques of generalized linear modelling were applied to worm burdens of 2268 mice artificially infected with Schistosoma mansoni and treated with oxamniquine and/or praziquantel. Models which maximized the Poisson likelihood were shown to be superior to those assuming either a log Normal or negative binomial error structure. Use of the models to calculate and compare ED values of 8 strains of S. mansoni, detect abnormal dose response and synergism and to pool data from several experiments is illustrated.

The study examines the rate of re-acquisition of Trichuris trichiura infection after treatment in two populations, one of mixed age and the other of children with known preintervention infection intensity. A population living in a Caribbean village was treated with mebendazole and the rate of reacquisition of infection of four age classes (2–4, 5–10, 11–30, 30+ years) monitored over a 20-month period. The reinfection rate was higher in the child age-classes indicating either that children are more exposed to infection or that adults slowly develop a partially effective acquired immunity. A cohort of children (mean age 4·5 years) was separated into 3 intensity categories on the basis of expelled worm burdens and their rate of reacquisition of infection monitored over a 12-month period. The rate of reinfection was directly and positively associated with initial infection status. This may indicate that children with low intensity infections are consistently less exposed to infection or that they have effective immune responses. The latter conclusion, however, would imply that they had acquired this immunity early in life, and so appears to contradict the suggestion that resistance is only slowly acquired by adults. Reconciling these two conclusions may require more sophisticated immunological models than have been suggested previously for geohelminthiases.

The purpose of this study was to determine whether predisposition to Heligmosomoides polygyrus and Aspiculuris tetraptera (Nematoda) exists within a naturally infected population of mice. A breeding mouse population was housed in a spacious arena in which endemic infections of H. polygyrus and A. tetraptera were present. H. polygyrus were over-dispersed in the mouse population. Prevalence reached 100% by the age of 3 weeks; intensity of infection increased to a peak in the 10 to 15-week-old mice, and remained high throughout life. A group of 73 mice was treated with pyrantel pamoate, and the expelled worms were counted. Mice were returned to the arena. Daily egg production was monitored 4, 8, 12 and 14 weeks after treatment. Mice were then killed and numbers of H. polygyrus and A. tetraptera were counted. Significant positive correlations were detected between numbers of H. polygyrus at first treatment and at necropsy, indicating the existence of predisposition. Similar results were obtained for A. tetraptera. Correlations improved when data were analysed by age class of mice. Analyses based on egg-count data during reinfection did not support the hypothesis of predisposition, however. A. tetraptera and H. polygyrus burdens were significantly correlated only in 3 to 4-week-old mice at the time of the treatment.

The cuticular permeability of anhydrobiotic 4th-stage juveniles of Ditylenchus dipsaci decreases during rehydration, as indicated by staining with osmium tetroxide, the measurement of permeability coefficients by the rate of uptake of tritiated water from a HOH/C-inulin bathing solution and by an increased ability to slow down the rate of water loss and to survive subsequent desiccation. The initial decrease in permeability coefficient is rapid, suggesting a physical effect due to the rehydration of the cuticle, followed by a slower reduction over the subsequent 1–4 h which is dependent upon metabolic activity. The reestablishment of the permeability barrier is sensitive to metabolic inhibitors which affect enzyme activity and post-transcriptional protein synthesis. Sodium iodoacetamide was the only inhibitor which affected maintenance of the permeability barrier. An Arrhenius plot of changes in cuticular permeability with temperature indicated a sharp increase in permeability at 40–50°C and brief exposure to diethyl ether resulted in loss of the permeability barrier, suggesting that a superficial layer, probably the epicuticle, is responsible for controlling cuticular permeability.

Excretions and secretions (ES) and somatic components of 4, 8, 12 and 16-week-old Taenia saginata metacestodes were biosynthetically radio-isotope labelled by incubating the larvae in the presence of [35S]methionine. Despite their small size, 4-week-old metacestodes produced as much isotope-labelled ES/parasite as older metacestodes, indicating a proportionately greater metabolic activity of the parasite at this age. In situ the 4-week-old metacestodes were surrounded by a marked granulomatous cellular infiltrate which had largely resolved around 8-week-old metacestodes. Examination of the isotope-labelled ES by SDS-PAGE revealed distinct age-specific components from 4- and 12-week-old metacestodes and other ES components which were produced by all the ages of metacestodes examined. In comparison the labelled somatic components were conserved. Antigenic characterization of the ES by immunoprecipitation against a panel of clinically defined bovine sera combined with SDS-PAGE analysis, identified some highly immunogenic parasite products and others which did not elicit an antibody response demonstrable by immunoprecipitation. These components are of interest in relation to the host/parasite relationship, to the construction of diagnostic assays for the detection of T. saginata cysticercosis, and to the immunity that cattle develop against this parasite.

A continuous succession of egg capsules is formed in the ootype of Protopolystoma xenopodis and released into the urinary bladder of the host, Xenopus laevis. Since egg capsules are passed out with the aquatic toad's urine several times a day, the rate of parasite egg production can be recorded accurately by direct counts. Temperature has a marked influence on the rate of egg output which doubles in response to a rise from 17 to 25 °C. Under constant temperature conditions regular egg collections from isolated toads infested with single Protopolystoma revealed that rates of production remain stable for periods of several weeks. The overall mean rate of egg production was 8·9 eggs/worm/day (e.w.d.) at 20·0±0·5 °C (based on 5 consecutive egg collections from 58 individual parasites). Significant differences were observed, however, between the mean rates of output from different hosts, ranging from 2·1 e.w.d. (s.d. = 0·6) to 17·7 e.w.d. (S.D. = 3·2). Neither differences in worm age nor host-factors could explain the observed range in output. Worms transferred to new hosts resumed egg production at pre-transfer rates, suggesting inherent differences in the capacity for egg production by individual parasites. Total production increased with increasing worm burden, but output per parasite was significantly reduced in groups of 2, 3 or 4. Whilst competition for some finite resource provides one interpretation, this observation could equally reflect a statistical phenomenon associated with the reduced chance of encountering groups of individuals which are heterogeneous for egg production as worm burden increases and sample size decreases.

The effects of duration of infection and of temperature and nourishment in cultures on development of free-living generations of Strongyloides stercoralis were studied quantitatively. Rhabditiform larvae, 228–353 μm long, were collected from infected dogs with or without prednisolone treatment using the Baermann apparatus. Cultures were carried out by the filter paper test-tube method under the following conditions: incubation temperature 15–40°C and faecal dilution 1:0–1:16. Rhabditiform larvae developed predominantly to free-living females at incubation temperatures of 15–30°C and low faecal dilutions, but filariform larvae appeared mainly under extreme conditions such as high temperature. Recovery rates of filariform larvae were inversely related to those of females. It was remarkable that high temperature, but not low faecal dilution, affected development of filariform larvae. Although the appearance of free-living males was constant in various environmental conditions, the present study indicated an increase in free-living males with the duration of infection. Thus, it seems that free-living males are already fixed as male in the egg stage, and potential female rhabditiform larvae differentiate into free-living females or filariform larvae depending on environmental factors. There is no marked difference in the development of rhabditiform larvae into filariform larvae in either the immunosuppressed dog or the intact dog.

The paper provides an overview of recent studies on the use of 75Se to tag larval schistosomes and to monitor their migration and distribution patterns in naive mice and those previously exposed to cercariae. The principles and techniques of radioassay and autoradiography in studying various aspects of 75Se-labelled larval schistosomes are described. The main shortcoming of radioassay in monitoring location and movement of labelled schistosomula is that some of the label dissociates from the schistosomula and accumulates in host tissues, notably the liver. Dissociated label is indistinguishable from schistosomula-bound label making monitoring of parasite migration extremely difficult. This difficulty is overcome by compressed tissue autoradiography where labelled schistosomula can be seen as reduced silver foci on an autoradiographic film, whereas dissociated label is too diffusely distributed to produce such reduced silver foci. Furthermore, using autoradiography, quantitative information on parasite migration in normal and immunized laboratory animals can be obtained that would be impossible using traditional recovery techniques. In addition to using 75Se tracer in migration studies, the radio-isotope has potential for elucidating various aspects of schistosome transmission ecology and snail population dynamics in natural waters.

The role of the larva of the alder fly Sialis lutaria as a host for Neoechinorhynchus rutili (Acanthocephala) has been investigated. Brown trout (Salmo trutta) infected with N. rutili were found to be feeding on S. lutaria larvae which contained juvenile acanthocephalans in their haemocoels. These acanthocephalans have been identified as N. rutili. A previous report of this host-parasite relationship indicated some form of host response to the larval acanthocephalan. Stained wax sections of S. lutaria larvae infected with N. rutili did not show any evidence of either a host response or encapsulation. Samples of S. lutaria larvae revealed an interesting pattern of infection. Only larvae of a particular size range were infected. An experiment to infect commercially obtained rainbow trout (Salmo gairdneri) with N. rutili by feeding them with infected S. lutaria larvae was successful. Since S. lutaria larvae are known to be prey items for trout it appears that this route of infection could commonly occur in the natural environment. Larval S. lutaria is considered as an additional intermediate host to several ostracod species which have been shown to play a role in the transmission of N. rutili.

Field observations at one site on brown trout (Salmo trutta) and three-spined sticklebacks (Gasterosteus aculeatus) concurrently infected with mature Neoechinorhynchus rutili, together with the knowledge that large trout can be piscivorous in habit led to the proposition that the post-cyclic transmission of N. rutili may occur between these fish species. This route of transmission has been suggested for a number of acanthocephalan species. A laboratory experiement was conducted and it was demonstrated that uninfected rainbow trout (Salmo gairdneri) can acquire a N. rutili infection as a result of feeding on sticklebacks already carrying established worms in their intestines. This finding may help to explain how N. rutili is found in a wide range of fish definitive hosts throughout the northern holarctic region. More generally this example provides further evidence of the flexibility within acanthocephalan life-history patterns.

Using biochemical genetic methods, we have distinguished 2 sibling species in the complex Bothrimonus nylandicus (Schneider, 1902), which infest 2 congeneric species of sole (Solea lascaris and Solea impar) on European coasts (Atlantic and Mediterranean). Neither of the parasite species is specific for either of the sole species, but one of them is present all year round, whereas the other is absent in the autumn and winter and only appears in the spring, subsequently disappearing at the end of the summer. Only S. impar lives in the Mediterranean, and is equally infested by both cestodes, whereas both species occur in the Atlantic and each of them is preferentially infested by 1 species of cestode. The shortness of the adult stage of the parasite in the definitive host and the presence of 2 life-cycles associated with competition between the 2 hosts in the Atlantic could be responsible for the biological differences observed and for maintaining the sibling species in sympatry.