Hymenolepis diminuta migrates up the small intestine in response to feeding the host 1 g of glucose. Locomotion during migration may result from fixed patterns of retrograde peristaltic-like waves in the strobila of the tapeworm which propel the organism against the normal expulsive forces in the small intestine. The peristaltic-like locomotory waves occur in a gradient along the strobila with a frequency of 24·9±0·9 cycles/min in the anterior segments of the worm, decreasing linearly to 6·6±1·4 cycles/min in the posterior segments of the worm. Chemical signals, isolated from the small intestine of fed hosts, which stimulate migration behaviour in vivo do not alter the behaviour of the scolex or strobila in vitro. Removal of the scolex containing the cerebral ganglia does not alter the frequency or pattern of locomotory activity in the strobila. After the worm is cut into pieces, each region generates the pattern of locomotory activity that is appropriate for that region. These data suggest that the peripheral nervous system, and not the central nervous system, is responsible for the coordination of the fixed patterns of locomotory activity in these tapeworms.

The in vivo effects of the anthelmintics taenifugin, VÚFB 14170 and VÚFB 15269 on the tegument of Hymenolepis fraterna have been examined by SEM, TEM and cytochemistry. The drugs were given to H. fraterna-infected mice on the 14th day post-infection in a single oral dose of 150, 200 and 200 mg/kg, respectively. By 72 h post-treatment, the drug-induced pathomorphological changes in the tegument indicated that all three drugs had a significant effect. Changes were most pronounced on the brush border and in the intercellular material. On the apical surface, there was blebbing as well as accumulation of membrane fragments over the microthrix tips and erosion of the brush border. The intercellular material was changed in structure, showing increased electron density in some areas and oedema of the intercellular spaces in other areas. There were also fractures of the tegument of variable depth, sometimes reaching to the parenchyma. These results suggest altered tegumental integrity and, occasionally, complete disruption of the selective permeability barrier created by the normal tegument. This suggestion is further supported by the penetration of ruthenium red into some tegumental areas and its distribution into the intercellular spaces, down to the parenchyma. The intrategumental lysosomes also appeared to be significantly activated. There was evidence of autophagy in both distal cytoplasm and tegumental cells. Mature and gravid proglottides were more susceptible to drug damage than those in the anterior strobila and neck.

The tentacular bulb of Grillotia erinaceus metacestodes consists of obliquely striated muscle fibres with obvious motor end-plates. In this study isometric tension recordings and intracellular microelectrodes have been used to record mechanical and electrical activity from single isolated bulbs. Bulbs were mechanically quiescent and displayed resting membrane polentials (RMP) in the region of −49 to −64 mV with a mean RMP of −56 mV (n = 60). The membrane potential varied with [K+]o in a manner consistent with the RMP being determined largely by the K+ equilibrium potential. High K+ solution (> 15 mM) caused membrane depolarization and contraction of the preparation with the contraction showing both phasic and tonic components. L-glutamate caused membrane depolarization, contraction of quiescent preparations and increased the amplitude of electrically evoked responses. In contrast, 5-HT, dopamine, histamine, adrenaline, GABA, noradrenaline and D-glutamate, at concentrations up to and including 10−3 M, were without apparent affect, although acetylcholine, at relatively high concentrations (≥ 10−4 M) slightly reduced the amplitude of field-evoked contractions.

The importance of host heterogeneity in generating aggregation was investigated using Heligmosomoides polygyrus (Nematoda) in laboratory mice. Parameters of infection were compared between inbred and outbred mice, between primary and challenge infection protocols, and between gavage and natural exposure protocols, to investigate the relative effects of innate resistance, acquired resistance and behaviour, respectively. Heterogeneity in acquired resistance was identified as the most consistent factor leading to variability and aggregation of H. polygyrus numbers in mice. This hypothesis was supported in two experiments where groups of mice did not develop resistance to challenge infection (use of certain inbred strains of mice and immunosuppression with corticosteroids in the drinking water) and where variability in worm numbers after the challenge infection was comparable with that after the primary infection. Heterogeneity in host behaviour, particularly in behaviours enhancing skin contact with larvae, also was associated with increased heterogeneity in worm burden, though not as consistently as heterogeneity in acquired resistance. Surprisingly, worm burdens were not more variable in outbred compared with inbred mice. Our data suggest that the relative contributions of innate resistance, acquired resistance and behaviour in generating variable worm burdens are likely to vary spatially and temporally.

The serum antibody responses of 124 people naturally exposed to Ascaris lumbricoides infection were analysed by immunoprecipitation of radio-isotope labelled 3rd- and 4th-stage larval Ascaris suum excretory and secretory antigens (L3/4 ES). Profiles of antigens recognized were visualized by polyacrylamide gel electrophoresis (SDS–PAGE), and the band intensities of the 12 major precipitated antigens were individually scored. Most subjects were seropositive, but considerable variation was observed in the amount of total and individual ES antigens precipitated. The sex- and age-related profiles of antibody levels followed similar patterns to those of egg output. In addition, total antibody scores of individuals were closely correlated (r = 0.47–0.52) with their eggs per gram of faeces (e.p.g.) collected 4 months after blood samples were taken. These findings suggest that antibody levels against larval ES antigens reflect recent exposure and are consistent with the hypothesis that establishment of adult worms is proportional to the number of larvae that recently migrated through the lung.

Cyclosporin A (CsA) induced significant changes in parasite morphology when administered to mice infected with Hymenolepis microstoma. Gross morphological damage consisted of proglottis swelling and the formation of protuberances from the worm surface, visible with a low-power dissecting microscope, occurring most frequently in the posterior third of the strobila. Gross morphology and ultrastructure were examined further using scanning and transmission electron microscopy. Swollen proglottides exhibited areas covered in small pits and fissures (diameter approximately 1–2 μm) but it was not possible to establish the significance of this damage. The brush-border and distal cytoplasm appeared largely intact although some evidence of swelling of the basal membrane invaginations and possible fluid accumulation was seen in drug-treated TEM sections. The apparent oedematous condition of many of the proglottides from drug-treated mice may indicate that CsA treatment mediates permeability changes in the worm surface membrane but the mechanisms by which this may occur remain to be elucidated. The effects of CsA on the morphology of H. microstoma correlate with the previously described anthelmintic activity of the drug against this parasite where CsA treatment dramatically reduces worm growth, retards migration into the bile duct and limits parasite survival.

Three ELISA assays, based on hyperimmune rabbit serum raised against adult cestode somatic antigen, were applied in this study for the detection of Taenia- and Echinococcus-specific antigens in host faeces. The first assay, using an antiserum against Taenia pisiformis antigen extract, was used in a time-course of T. pisiformis experimental infection in dogs. The assay was shown to be considerably more sensitive than microscopical detection of eggs in faeces. Antigen was present in faeces before patency and antigen levels were independent of T. pisiformis egg output. The second assay, involving a test for human taeniasis based on antibodies against T. solium, was applied in two field studies carried out in China and Guatemala. The test was highly specific, no false positive reactions occurred with human faecal samples and the test was capable of diagnosing individuals who would not have been detected by coproscopy or treatment to recover the tapeworm. A third assay was designed for E. granulosus and demonstrated 87·5% sensitivity and 96·5% specificity with samples from naturally and experimentally infected dogs with Echinococcus or Taenia infections. In both the human Taenia and canine Echinococcus studies antigen could be detected in faecal samples from infected hosts stored in 5% formalin for 6 months. Further refinements to these tests for field application are discussed.

Two autogenic (Triaenophorus crassus and T. nodulosus) and four allogenic (Diphyllobothrium latum, D. dendriticum, D. ditremum and Schistocephalus solidus) larval cestode species were found in 13 out of 31 fish species studied from the Bothnian Bay, NE Baltic. Gasterosteus aculeatus was the most heavily infected fish with 4 larval cestode species; for two of them (D. ditremum and S. solidus) the three-spined stickleback was found to be the required fish intermediate host. Among allogenic cestode species, those restricted to different definitive host species segregated their larval population in relation to the fish host, while, for example, D. ditremum and S. solidus, both maturing in fish-eating birds, had the highest percentage of co-occurrences. D. dendriticum, which had the widest range of definitive hosts, was found in the greatest number (8) of fish species and co-occurred with all other species found except T. crassus. The two autogenic species totally segregated their larval population from each other although they both require pike as definitive host. The ecological and evolutionary relationships behind the patterns found for larval cestodes are discussed.

An antibody competition enzyme-linked immunosorbent assay (ELISA) using 4 different monoclonal antibodies (MAb) raised against major antigens (Antigen 5 and Antigen B) of Echinococcus granulosus was evaluated for the diagnosis of human hydatidosis. The competition assay, using anti-Ag5 MAb 24.14, detected specific antibodies in 70% (131/188) of sera from patients with surgically confirmed E. granulosus infection and 38·5% (10/26) of sera from patients with E. multilocularis infection. None of the sera from patients with Taenia solium cysticercosis (10), T. saginata (2), filariasis (22), strongyloidiasis (19), fascioliasis (4), bilharziasis (4) and amoebiasis (2) tested were positive using a cut-off point established through reaction between MAb 24.14 and normal human sera. The combined use of the MAb 24.14-based competition ELISA with the conventional antibody-binding assay provides a highly sensitive (92·8%) and specific screening system for human hydatid disease diagnosis.

A double-blind placebo trial was conducted to determine the effect of moderate to high loads of Trichuris trichiura (whipworm) infection on the cognitive functions of 159 school children (age 9–12 years) in Jamaica. Infected children were randomly assigned to Treatment or Placebo groups. A third group of randomly selected uninfected children were assigned to a Control for comparative purposes. The improvement in cognitive function was evaluated using a stepwise multiple linear regression, designed to control for any confounding variables. The expulsion of worms led to a significant improvement in tests of auditory short-term memory (P < 0.02; P < 0.01), and a highly significant improvement in the scanning and retrieval of long-term memory (P < 0.001). After 9 weeks, treated children were no longer significantly different from an uninfected Control group in these three tests of cognitive function. The removal of T. trichiura was more important than Ascaris lumbricoides in determining this improvement. The results suggest that whipworm infection has an adverse effect on certain cognitive functions which is reversible by therapy.

Development of the inflammatory response of rainbow trout to experimental infections with Diphyllobothrium dendriticum plerocercoids is described using light and electron microscopy. The cellular response to plerocercoids occurred within 2 weeks post-infection (p.i.). This was followed by an increase in leucocyte numbers during weeks 3–6 p.i., with full encapsulation of plerocercoids by week 6 p.i. Neutrophils were the first leucocytes to engage the developing plerocercoid, followed by large influxes of macrophages which transformed into epithelioid cells. With longer times p.i. the accumulation of different leucocyte types increased, and a blood vascular network developed. Full development of the composite cyst was characterized by fibroplasia, particularly at the periphery of the cyst, and the subsequent deposition of a collagenous tissue matrix. Enzyme-linked immunosorbent assay (ELISA) examination of serum samples taken over the 20 week period showed that specific anti-D. dendriticum antibody titres were first detected at 5 weeks p.i. and increased to a maximum by 11 weeks p.i.

Responses to Taenia taeniaeformis infection were studied in mice with severe combined immunodeficiency (scid), which lack functional T and B lymphocytes. In the early phase of infection, accumulation of polymorphonuclear leucocytes (PML) occurred around the larvae in the liver of scid mice and their immunocompetent counterparts, C.B-17, (a BALB/c strain, genetically resistant to this parasite). PML accumulation continued until encapsulation of developing larvae by fibroblasts (14 days p.i.), and subsequent fibrosis resulted in granuloma formation. No infiltration of eosinophils or macrophages around larvae was observed in scid mice prior to granuloma formation, while in C.B-17 mice infiltration was observed as early as 5 days p.i., when specific antibodies could not be detected in the circulation. Most larvae were destroyed by 14 days p.i. in C.B-17 mice. In scid mice the larvae survived but the host capsules (cysts) were thin and most contained blood at 42 days p.i. In these cysts, inflammatory cells were observed on the larval surface and in invaded parasite tissue. Hepatocyte coagulation necrosis adjacent to larvae was commonly found in C.B-17 mice by 5 days p.i., while it did not occur in scid mice throughout these experiments. These results suggest that in host responses to larval T. taeniaeformis, PML accumulation and encapsulation by fibrosis are T and B cell independent, while eosinophil and macrophage infiltration, as well as resistance to infection, are T and/or B cell dependent. Additionally, there may be an association between host cell necrosis around larvae and T and/or B cell responses.

The distribution of the fluorescent ivermectin derivative (4″ 5,7 dimethyl bodipy proprionylivermectin, referred to here as bodipy ivermectin) was studied in muscle vesicle membranes from the parasite Ascaris suum. Incubation in bodipy ivermectin, at concentrations greater than 1 ng/ml, produced a dose-dependent fluorescence in the vesicles. The level of fluorescence was not depressed (but increased) by prior incubation with 1 μM unlabelled ivermectin. This observation suggested that most of the bodipy ivermectin was free in the lipid phase of the membrane and not associated with a receptor. The trypan blue quenching technique showed that the bodipy ivermectin did not cross the membrane bilayer but remained in the outer monolayer. Lateral mobility of the probe in the membrane was studied using the fluorescence recovery after photobleaching (FRAP) technique. The lateral diffusion coefficient (DL) was 14.0 x 10−10 cm2/s which was nearly three times faster than the lipid probe octadecanoyl-aminofluorescein in membranes from the same preparations; only 46% of the probe was mobile, showing that within a 1.2 μm radius the distribution of the bodipy ivermectin in the membrane was not homogeneous. These observations are used to suggest that: the site of action of livermectin is located in the outer monolayer of the membrane (possibly on the Cl− channel); and that the speed of onset of action in isolated membrane preparations may be limited by diffusion in the membrane.

Density-dependence in worm establishment, numbers, biomass and larval production were examined in primary infections of 0, 10, 40, 80 and 160 larvae of the lung nematode, Rhabdias bufonis in the common toad, Bufo bufo. The infection procedure established 4 non-overlapping levels of infection which persisted until 6 weeks post-infection (p.i.), after which there was an overall decline up to 12 weeks p.i. Worm numbers had no direct effect on adult worm survival but temporal changes in worm weight were density-dependent. Adult worm establishment in the lungs declined significantly as the numbers of worms in the lungs increased. At the lowest exposure dose, 86% of the larvae administered reached maturity in the lungs while at the highest, only 37% did so. Also, the numbers of immature larvae outside the lungs increased as adult worm numbers increased. Both features provide evidence for a threshold limit to the numbers of worms maturing in the lungs. Worm numbers also affected larval output per host and per capita fecundity. A significant positive relationship between per capita fecundity and per capita worm weight suggested that density-dependence acted primarily to constrain the growth of individual worms. Finally, the constraints imposed on worm growth and fecundity were apparently relaxed when worm density decreased, providing evidence for density-dependent flexibility in per capita fecundity. Density-dependence in worm establishment and per capita fecundity are mechanisms which may potentially regulate this host–parasite interaction in the field. Both mechanisms may be functionally related to physical space limitations in the lungs, within which worms must compete for finite nutrients.

Using data sets derived from published literature, the contribution of congeneric species to helminth component community richness is evaluated. Consideration of the frequency distribution of congeners in relation to host and parasite groups reveals that the distributions are unimodal, that singletons are the commonest class and that the frequency of occurrence of congeners decreases with increasing number of species per genus. Congeners may be found in any group of hosts or parasites, but are more common amongst cestodes of aquatic birds. Two patterns of occurrence of congeneric species are recognized: one in which from a few to multiple congeners are found within a single helminth genus, exemplified by dactylogyrid monogeneans and cloacinid nematodes, and the other in which there is a simultaneous occurrence of congenerics and confamilials such that there are several genera involved, but each represented by fewer species, exemplified by strongyles in horses. The question of whether these patterns can be considered examples of species flocks is discussed. We conclude that multiple congeners and species flocks are interesting phenomena but, except in isolated cases, they make insignificant contributions to community richness.

This study examines the persistence of predisposition to Ascaris lumbricoides and Trichuris trichiura during repeated chemotherapy in an urban community in Kuala Lumpur, Malaysia. Significant predisposition was observed over 2 periods of reinfection with and without age-standardization of data. Analysis of different age groups indicated that predisposition was most strongly detectable in the younger age classes. The intensities of infection with both parasites were strongly correlated at each cycle of intervention, suggesting that individuals were similarly predisposed to both species.