The genetic structure of Anisakis physeteris from the Mediterranean Sea has been analysed electrophoretically at 22 enzyme loci. The samples studied, although differing in the life-stage (larvae and adults), and in the host (the fishes Micromesistius poutassou and Trachurus trachurus, and the sperm whale Physeter macrocephalus) were genetically homogeneous. Of these loci 11 (Ldh, Sod, Np, Adk-2, Pgm-1, Est-1, Est-2, Acph-1, Acph-2, Lap-2 and Ca) were found to be monomorphic, while the other 11 (Sdh, Mdh, ldh, 6-Pgdh, G3pdh, Got, Adk-1, Pgm-2, Lap-1, Mpi and Gpi) showed from 2 to 7 alleles. The following values of genetic variability were estimated: He = 0·ll, P = 0·50, A = 1·95. Distinct alleles were found between A. physeteris and the A. simplex complex at 19 out of the 22 loci studied, and only few rare alleles were shared at the remaining 3 loci. The genetic divergence between A. physeteris and A. simplex A and B is therefore very high, the values of Nei’s index D being 7·384 and 6·443 respectively (I = 0·001 and 0·002). The assignation of A. physeteris and the A. simplex complex to two distinct subgenera, Skrjabinisakis and Anisakis, as proposed by Mosgovoy on a morphological basis, appears to be fully justified according to our genetic data.

Trilocularia acanthiaevulgaris occurs in the stomach and spiral valve of the spiny dogfish. Statistical analyses show that the stomach and spiral valve worms of male fish and the stomach worms of female fish exhibit seasonal trends in prevalence and mean worm burden, with peaks occurring in May, June and July of each year. Spiral valve worms of female fish do not show this trend. Calculation of the product-moment correlation coefficient shows that the peak in the number of stomach worms occurs approximately 1 month before that of spiral valve worms in male fish. Strobilization of the adult spiral valve worms and development of the resulting free proglottides is also seasonal, and takes place in June/July in both sexes. Seasonal trends in prevalence, mean worm burden and maturation of T. acanthiaevulgaris may be related to water temperature, and the cyclical changes in levels of reproductive hormones and thyroid activity associated with migration and mating of spiny dogfish. It is suggested that the availability of infected intermediate hosts and diet of the dogfish may also be important in explaining the seasonality of infection.

Onchocerca volvulus proteins labelled with 125I were immunoprecipitated with onchocerciasis and lymphatic filariasis human serum pools in order to differentiate between cross-reacting and non-cross-reacting antigens. Analysis of the immunoprecipitates by two-dimensional gel electrophoresis revealed that all high molecular weight (Mr) O. volvulus antigens cross-reacted with the lymphatic filariasis serum pools. We observed, however, that at least 8 0. volvulus antigens were specifically immunoprecipitated only by the onchocerciasis serum pools, with Mr ranging from 20000 up to 43000 Daltons. These results suggest that the lower MrO. volvulus antigens are more species specific than the other antigens. The significance of these findings for the immunodiagnosis of onchocerciasis is discussed.

Intact, viable adults, infective and newborn larvae of Trichinella pseudospiralis were surface labelled with 125I by the chloramine T method and labelled proteins were compared with those obtained from equivalent stages of T. spiralis. Electron-microscope autoradiography determined that labelled proteins were restricted to the cuticle for all stages of both isolates. Comparative polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDS–PAGE), using thin gradient gel slabs, of proteins obtained from each stage, demonstrated that the profile of surface-labelled proteins of T. pseudospiralis were restricted in number, stage specific, and similar to equivalent proteins of T. spiralis both in size and in their organization into aggregates. The stage-specific profiles of surface-labelled proteins derived from newborn larvae were indistinguishable, but differences were noted between adults and infective larvae of the two isolates. These differences in protein structure were confirmed by two dimensional mapping of tryptic peptides. Stage-specific profiles were also obtained when [35S]methionine biosynthetically labelled secretions of the 3 stages of T. pseudospiralis were compared by SDS–PAGE. Comparison of the profiles obtained with secretions for respective stages of T. spiralis again failed to distinguish newborn larvae, but adults and infective larvae of T. spiralis and T. pseudospiralis displayed a mixture of common and species-specific proteins. These findings are discussed in relation to the different pathology associated with infection with two isolates.

Absorption of glucose in vitro by enteric stages of Trichinella spiralis was examined in worms isolated at different times following infection. Glucose absorption by 6-h-old worms was similar to that seen during moulting (24 h post-infection (p.i.)). As embryogenesis began (48 h p.i.) glucose absorption in vitro by the parasite rose dramatically to a peak in 72-h-old worms. Absorption of glucose in vitro remained high in 96-h-old worms but as larviposition began (120 h p.i.) glucose uptake by T. spiralis dropped significantly. Glucose absorption by worms isolated from the host during the primary immune response was unaffected. Glucose absorption in vitro remained at similar levels in worms isolated between 120 and 312 h p.i. The percentage of absorbed label incorporated into parasite tissues was greatest in 48- and 312-h-old worms. Glucose uptake in vitro by pre-adult and adult worms changed with time and these changes accompanied specific events in the biology of the parasite.

Praziquantel is a broad-spectrum anthelmintic active against schistosome species which are major parasites of man. Two major effects on Schistosoma mansoni have been demonstrated; (i) spastic paralysis of the parasite musculature, possibly arising as a consequence of an influx of Ca2+ into the worm (Pax, Bennett & Fetterer, 1978; Coles, 1979) and (ii) vacuolation and degeneration of the worm tegument (Becker, Mehlhorn, Andrews, Thomas & Eckert, 1980). These events may contribute to the elimination of schistosomes in vivo, but this elimination may partly be dependent on the host immune response as infected T-cell-deprived mice are less able than immunologically intact animals to reduce their worm burdens following drug treatment (Doenhoff, Harrison, Sabah, Murare, Dunne & Hassounah, 1982). This latter observation raises the possibility that praziquantel may lower the ability of the parasite to evade host immunity by increasing the exposure of parasite antigens capable of acting as targets for host antibody, or antibody-armed cells at the worm surface. Consistent with this idea is the observation that adult schistosomes in praziquantel-treated mice are invaded a few hours after treatment by host granulocytes (Mehlhorn, Becker, Andrews, Thomas & Frenkel, 1981).

An experimental system is described for the study of the community dynamics of helminth–host populations, using Heligmosomoides polygyrus in the laboratory mouse. The results of a preliminary experiment using closed populations of 50 mice revealed that coexistence of host and parasite occurs for at least 4 months in the absence of immigration, with the generation of epidemiological patterns similar to those observed in the real world. In well-nourished mice the prevalence and intensity of infection initially increased with time and then declined, probably as a result of acquired immunity. The prevalence and intensity of infection increased less rapidly among hosts fed on a low protein diet, but continued to rise over the entire duration of the experiment. This continued rise is interpreted as evidence of a negative effect of protein malnutrition on host immunocompetence. The frequency distributions of parasite numbers/host were over-dispersed in each mouse population. No density dependence in parasite fecundity was detected. Aspiculuris tetraptera was also found to be present in the mouse populations. This parasite was not transmitted between mice fed on a high protein diet, but rose to a prevalence of 80 % in protein malnourished animals. No association between the intensity of A. tetraptera and H. polygyrus could be detected in individual hosts. The results are discussed in terms of the future potential of the system for the investigation of the role of acquired immunity (and its genetic control) in the generation of epidemiological patterns.

Three distinct muscle types have been identified within the metacestode of Grillotia erinaceus. These consist of peripheral somatic myofibres plus two muscle systems directly involved in parasite attachment to the host, i.e. the tentacular bulb and its antagonistic retractor muscle. In common with other cestodes the somatic muscle consists of smooth-type fibres running longitudinally and obliquely to the main body axis. The retractor muscle consists of myofibres with centrally displaced nuclei. Upon contraction these latter fibres become spirally orientated causing the muscle to coil and lateral membranes to become elevated as spikes. Definitive nerve processes have not been identified within somatic or retractor muscle. Individual tentacular bulbs form the proximal terminus for a closed hydraulic system. Each bulb consists of overlapping, contrarotating myofibres which display obvious striations; the striations appear in alternate fibres to be in transverse and oblique planes. Adjacent myofibres are separated by approximately 0·5 μm, possess abundant mitochondria and have shallow t-tubules plus associated vesicles of sarcoplasmic reticulum at each Z line. Thick myofilaments are surrounded by 13, shared, thin myofilaments. Close neuronal control for the bulb muscle is suggested by the presence of obvious motor end-plates which contain both lucent and dense neurovesicles.

The results are presented of an experimental investigation of the relationship between faecal egg counts and worm burden in outbred MF1 mice infected with Heligmosomoides polygyrus (Nematoda). The sex-ratio of the adult parasites was found to be significantly female biased, but independent of parasite burden. Evidence was also found to suggest a significant association between parasite density and mating success. The linear logarithmic relationship (gradient of approximately 2) between the variance and mean of repeated egg counts from individual mice could not be disrupted by controlled experimental conditions, and is therefore concluded to be an inherent feature of the biology of helminth-host interactions. A significant positive association was detected between host faecal output and parasite fecundity; further investigation of the cause of this association is now required. Average faecal production was found to be inversely related to worm burden. In combination, the above two factors account partly, but not completely, for the observed density dependence in the absolute rate of parasite egg production. Two epidemiological consequences of the relationship between faecal production and parasite fecundity are discussed. First, absolute rates of egg production can only be estimated by temporal egg counts (epd). Secondly, measurements of egg production/g of faecal material (epg) are more reliable indicators of worm burden than measurements of epd. Both faecal output and worm fecundity respond as might be predicted to a period of host food deprivation; faecal egestion and measurements of epd are signifcantly depressed, and measurements of epg are significantly increased. The data are consistent with the hypothesis that egg production and faecal output are causally associated, but that other factors relating to parasite density also influence egg production. Of the possible causes for the high variability in parasite egg production between mice harbouring low number of worms, the most likely explanation seems to be host heterogeneity (possible genetic in origin). This is discussed in relation to similar patterns observed in data collected from human populations in areas of endemic helminth infection.

Previously we reported the isolation of several Escherichia coli clones expressing fragments of Taenia taeniaeformis antigens as β-galactosidase fused proteins (Bowtell, Saint, Rickard & Mitchell, 1984). Here we describe the isolation of additional antigen-expressing clones from a larval cDNA library and the assignment of these clones to 7 antigen families. These were isolated with a polyspecific rabbit antiserum raised to the oncosphere. Since this serum was capable of reacting with a large number of antigens, it was important to develop techniques for rapidly determining the identity of the native T. taeniaeformis molecule corresponding to a cloned antigen gene. These included active immunization of rabbits with fused proteins and several techniques involving affinity purification on immobilized fused proteins. The reactivity of the antigen-positive clones with sera from humans infected with related parasites was also assessed. Finally, immunization of mice with several fused proteins failed to protect against subsequent infection, although antigens previously identified as candidate host-protective antigens (Bowtell, Mitchell, Anders, Lightowlers & Rickard, 1983) have yet to be identified in the expression library.

Recently, some authors (Kennedy, 1981; Price & Clancy, 1983) have argued that there are fundamental differences between the communities of helminths in fish and bird hosts. Such differences are foreshadowed by the work of Dogiel (1964) and are apparent from survey data (e.g. Threlfall, 1967; Bakke, 1972; Hair & Holmes, 1975 on birds, and compare Chubb, 1963; Mishra & Chubb, 1969; Wootten, 1973; Ingham & Dronen, 1980 on fish). Questions still remain, however, as to whether the distinctions are truly justified and whether the differences are really fundamental. In this paper, we address these questions by examining helminth diversity in a series of hosts. We then discuss and provide explanations for the observed differences.

The adult liver fluke, Fasciola hepatica, inhabits the bile duct of its final host, usually cattle or sheep. The veterinary aspects of infection with F. hepatica can represent a major problem and consequently fascioliasis can have serious economic effects. As recently as 1972 the loss in revenue due to liver fluke infestations in the UK was estimated at an incredible £50 million per annum (Coles, 1975). Not only can F. hepatica infect cattle and sheep, but also outbreaks of human disease have been reported. The last serious outbreak in Britain was in 1968 when at least 49 cases were identified (Ashton, Boardman, D'Sa, Everall & Houghton, 1970; Hardman, Jones & Davies, 1970).