Plasmodium falciparum-infected erythrocytes (IRBC) synthesize 3 histidine-rich proteins: HRP-I or the knob-associated HRP, HRP-II and HRP-III or SHARP. In order to distinguish these proteins immunochemically we prepared monoclonal antibodies which react with HRP-I, HRP-II and HRP-III, and rabbit antisera against synthetic peptides derived from the HRP-II and HRP-III sequences. A comparative analysis of diverse P. falciparum parasites was made using these antibodies and immunoprecipitation or Western blotting. HRP-I (Mr 80000–115000) was identified in all knob-positive P. falciparum parasites including isolates examined directly from Gambian patients. However, this protein was of lower abundance in these isolates and in 6 knob-positive, culture-adapted parasites compared to Aotus monkey-adapted parasites or culture-adapted parasites studied previously. HRP-II (Mr 60000–105000) was identified in all P. falciparum parasites regardless of knob-phenotype, and was recovered from culture supernatants as a secreted water-soluble protein. Within IRBC, HRP-II was found as a complex of several closely spaced bands. Cell surface radio-iodination of IRBC from several isolates and immunoprecipitation with a rabbit antiserum against the HRP-II repeat sequence identified HRP-II as a surface-exposed protein. Like HRP-I, the abundance of HRP-II was lower in the Gambian isolates than with Aotus monkey-adapted parasites studied earlier. Neither HRP-I nor HRP-II were identified in a knob-positive isolate of P. malariae collected from a Gambian patient. Analogues of these HRP were also absent from asexual parasites of diverse primate and murine malaria species screened with this panel of antibodies. HRP-III (Mr 40000–55000) was distinguished by its lower apparent size and by specific reaction with rabbit antibody against its 5-mer repeat sequence. HRP-III was of lowest abundance compared with the other two HRP. These antibody reagents and distinguishing properties should prove useful in studies on the separate functions of the 3 P. falciparum HRP.

A range of monoclonal antibodies specific for Plasmodium falciparum were tested in vitro for their abilities to inhibit the multiplication of a partially synchronized culture of P. falciparum, to augment the phagocytosis of the parasites by macrophages, and to enhance the killing of parasites by peritoneal cells depleted of adherent cells. Seven of 17 monoclonal antibodies, ranging from culture supernatant fluid and ascitic fluid to purified IgG, showed dose- and time-dependent inhibition of parasite growth in vitro. At a concentration of 0·6 mg/ml, the inhibitory capacity of these monoclonal IgGs was above 94% over a 3-day culture period, much higher than that of the relevant polyclonal IgG. Four of 6 monoclonal antibodies tested augmented the phagocytosis of the parasites by macrophages, which occurred as a result of opsonization of the parasites. Four of 7 monoclonal antibodies examined showed cytotoxic activity on malaria parasites. Peritoneal cells depleted of adherent cells were capable of killing the parasites in the presence of monoclonal antibodies. These results indicate that there may be ‘monofunction’, ‘bifunction’, and ‘multifunction’ types of monoclonal antibodies against P. falciparum. The putative protective antigen of malaria parasites purified by ‘multifunctional monoclonal antibody’ affinity chromatography may have potential interest as a vaccine against the parasite or as an immunodiagnostic reagent for human malaria.

We have examined the interaction between Schistosoma mansoni and a cytotoxin from Pseudomonas aeruginosa known to affect a variety of cell types through the formation of membrane pores. The killing effect of the cytotoxin on S. mansoni in vitro was strongly dependent on the parasite developmental stage. Skin schistosomula were most sensitive, while 4-week-old or older parasites were less so. In contrast, lung schistosomula were relatively resistant and juvenile mesenteric forms younger than 28 days were almost completely refractory to the action of the toxin. A sharp increase in sensitivity to the toxin was observed between 27 and 28 days of parasite age with a parasite length of about 1·80 mm appearing as the threshold. Thus, the schistosome sensitivity to the cytotoxin changed during parasite development in a way similar to the known sensitivity of the worms to in vitro immune attack. Killing of the parasites by the cytotoxin was preceded by the formation of vesicles which, in the case of adult worms, detached easily from the parasites. Evidence obtained by electron microscopy and by immunofluorescent assays with living worms demonstrated that the outer parasite membrane participated in the formation of the vesicle membrane. Thus, the cytotoxin may be a useful tracer for changes in the properties of the schistosome surface membrane during parasite development.

Of the surface antigens identified by radio-iodination, two-dimensional gel analyses showed no similarities between those of Schistosoma haematobium and Schistosoma mansoni, thus providing a basis for the species specificity of these antigens described previously (Simpson, Knight, Hagan, Hodgson, Wilkins & Smithers (1985) Parasitology 90, 499–508). The surface antigens of S. haematobium were glycosylated and comprised an acidic polypeptide of Mr 17000 as well as a complex set of polypeptides of approximate pI 6–7, which resolved in the Mr range 20000–30000. At least one of the lower Mr forms of this complex is also present in the adult worm. Limited cross-reaction was observed with S. mansoni infection sera and this may be due to a shared carbohydrate epitope. In contrast, extensive cross-reaction was observed using sera from mice immunized with S. bovis. This pattern parallels the species-specificity of vaccine-induced immunity. Extensive cross-reaction was also observed within cell-free translation products of m-RNA from adult worms of S. haematobium and S. mansoni by use of heterologous human infection sera. The few antigens which were species-specific may represent surface antigens.

Larval Schistosoma mansoni have been shown to induce morphological changes to the internal calcium reserves (in particular the calcareous inclusions in Type A calcium cells and to the inner, nacreous layer of the shell) of Biomphalaria glabrata within 48 h of miracidial penetration. Control experiments have shown that these changes were not due to either the experimental procedures used, mechanical damage or to starvation effects. The effects were, however, analogous to experimentally induced acidosis, suggesting that the rapidly transforming miracidium-sporocyst quickly induces changes in the host's metabolism, presumably by the production and release of CO2 and waste metabolites into the haemolymph.

A double antibody sandwich ELISA technique has been developed for detection of antigens of African trypanosomes present in the sera of infected mammals. The assay uses a high titre, high affinity rabbit antiserum made to purified membranes of procyclic trypanosomes as ‘capture’ reagent and a mixture of three biotin-labelled trypanosome-specific monoclonal antibodies as detecting reagent. The monoclonal antibodies were chosen on the basis of their specificity for surface membrane antigens of Trypanosoma brucei spp., the relative abundance and solubility of their specific antigen in aqueous solvents (including serum), and the fact that each monoclonal antibody binds to distinct epitopes on the same antigen molecule. Thus, antigen capture from serum and subsequent detection was achieved using as little as 10 ng/ml of whole trypanosome lysate, or the equivalent of 5000 trypanosomes/ml when solubilized material was added to normal serum in an artificial system. Using the optimized assay, antigen was detected in the sera of trypanosome-infected mice as early as 2 days after infection with T. b. rhodesiense. The results indicate that the assay allows detection of low concentrations of specific membrane antigens of T. brucei spp. of African trypanosomes and thus may have immunodiagnostic utility.

The plasma of mice infected with pleomorphic Trypanosoma brucei brucei contains a peptidase which has the same electrophoretic mobility on starch gels as a parasite peptidase. An enzyme with this electrophoretic mobility was not detected in the plasma of uninfected mice. The molecular weight of this enzyme in either parasite lysate or plasma from infected mice was approximately 40000 Da when assayed on a size exclusion column using high-performance liquid chromatography. The enzyme can cleave the dipeptides leu-ala, val-leu and pro-leu, but not the dipeptide phe-ala. The enzyme also cleaved the tripeptides tyr-tyr-tyr and leu-gly-gly. Another parasite peptidase which migrates on starch gels to a different position than the above-mentioned peptidase cleaved the dipeptides leu-ala, val-leu and pro-leu but could not cleave the tripeptides tyr-tyr-tyr or leu-gly-gly. Furthermore, incubation of this parasite peptidase with normal mouse plasma at 37 °C resulted in an apparent loss of detectable activity. It is postulated that the plasma of mice modifies either the charge or enzymic activity of this peptidase. We speculate that the parasite peptidase present in the plasma of mice infected with T. brucei could contribute to pathogenesis.

A population of eels Anguilla anguilla from Lough Derg, R. Shannon, Ireland, harbouring infections of both Acanthocephalus lucii and A. anguillae was studied over three years. Both parasite species had the same intermediate host and eels appeared to be the only definitive host for A. anguillae. Throughout the whole period, A. lucii was the dominant parasite, was over-dispersed throughout the eel population and most frequently occurred as a single species infection. A. anguillae was far less common, its dispersion was close to random at most times and it almost invariably occurred as a mixed species infection. The proportions of the two species remained fairly constant over the period. Despite some indication of site selection in the intestine, the distribution of both species overlapped considerably and there was no evidence of competitive displacement of one species by the other or of resource partitioning in space. The life-histories of both species were similar: they infected eels, bred and were lost from fish at the same time of year and there was no indication of resource partitioning in time. Congeneric species of acanthocephalans can thus co-exist in apparently stable equilibrium in fish as predicted and without any evidence of interactions, but it is still considered that exploitation competition between the species may be occurring in eels.

Primary infections of Heligmosomoides polygyrus were studied in adult male CD1 mice fed on isoenergetic synthetic diets containing either 2% or 20% protein (casein). A slight reduction in food intake was observed during infection, and this was unaffected by diet. Protein deficiency was also found to have no effect upon worm establishment. Evidence was found, though, to suggest that the worms have a more severe effect upon the host in protein-deficient mice. Hypoalbuminaemia was observed due to diet and also infection, and this was synergistic. There was an increase in non-albumin plasma protein during infection which was not effected by diet. The circulating urea concentration was reduced during protein deficiency, as was the level of essential amino acids, but non-essential amino acid levels were raised. An increase in the levels of urea and essential amino acids was observed at day 4 of infection in mice on the 20% diet, but not on the 2% diet. Splenic atrophy occurred during infection, but the splanomegaly that occurred early during infection was proportionally greater in protein-deficient mice. These results are discussed in terms of the pathophysiology of both protein deficiency and infection, and comparisons are made with human malnutrition syndromes.

Studies of patterns of reinfection with four species of intestinal nematodes (Ascaris, hookworm, Trichuris and Enterobius) in 174 individual patients following chemotherapeutic treatment revealed statistical evidence for predisposition to heavy or light infection (relative to the average level in the overall population). Analyses of associations between the abundances of the four species of nematodes within a combined sample of 525 worm burdens showed significant correlations between 5 out of the 6 possible pair-wise comparisons between species. The relevance of these results to the design of control programmes based on chemotherapeutic application is discussed.

The distribution and abundance of Enterobius vermicularis in a fishing community in South India, as determined by counting worms expelled following mass anthelmintic chemotherapy, was examined in samples of patients stratified by age, sex and family grouping. The results of a worm expulsion study in January 1984 are compared with those of a second expulsion programme in November 1984, following an 11-month period of reinfection. The prevalence of Enterobius infection was consistently high in all age groups of both males and females. A comparison of the overall prevalence and intensity of infection in the January and November surveys revealed significant increases in both the percent infected and the mean number of worms harboured in November relative to the initial level. No significant trends in the intensity of Enterobius according to host age or sex were detected in either survey. The frequency distribution of Enterobius was found to be highly aggregated in the population as a whole and within age groups. At both sampling dates, the most heavily infected 25% of the community harboured over 90% of the total pinworms recovered. There was a significant pattern within most age groups for individuals to re-acquire worm burdens of a similar magnitude to their initial pre-treatment burdens. Heavy infections were found to be associated with household. A selective or targetted approach to treatment of heavily infected individuals or households is likely to be an efficient means of reducing parasite abundance on a community-wide basis. It must be stressed, however, that treatment must be applied at frequent intervals in order to achieve a long-term reduction in pinworm abundance and to avoid the possibility of increasing the intensity of infection, as was observed in this community.

Cyathocotyle bushiensis Khan 1962 is a digenean intestinal parasite of ducks that appears to be involved in seasonal mortality of the definitive host. Temperature dependence of egg hatching and miracidial survival at 25%C were experimentally investigated as part of a study on transmission of the larval stages. Maximum percentage of hatching was obtained at a temperature of 25%C, at which the average hatching time was 21·7 days. The average hatching time decreased linearly from 38·9 days to 9·8 days between 18 and 28%C. Eggs exposed to cold (4%C) prior to incubation at 25%C were significantly less successful in hatching than fresh eggs incubated at the same temperature. Their hatching percentage was much reduced and their average hatching time was increased. Similarly, eggs collected in late autumn (as opposed to summer) and incubated at 23%C had significantly lower hatching success and significantly increased average hatching time. At 25%C, the average life-span of the miracidia was 8·8 h. These results are compared with similar data from other digenean species and their significance is discussed in relation to transmission to the first intermediate host in climatic conditions prevalent in endemic areas.

A mathematical model of the parasitic phase of the life-cycle of Ostertagia ostertagi in calves is described. The model is used in the re-analysis of previously published data from a long-term trickle infection experiment in which groups of calves were infected daily with graded doses of 3rd-stage (L3) larvae. The results of the analysis are consistent with the hypothesis that the observed changes in the intensity of infection in the calves were the result of a decline in the proportional establishment of ingested L3 larvae, and a rise in the death rate of the 5th-stage worms as the duration of exposure to infection increased. The proportion of ingested L3 larvae that become established in the mucosa can be described as an exponential decay function of the duration of the infection. Within the range of trickle intensities investigated, the function appears to vary independently of the level of exposure to infection. In contrast, the rate of mortality of the 5th-stage worms appears to be an increasing linear function of the total cumulative number of 3rd-stage larvae administered.

The decline in faecal egg counts, characteristic of calves which have been experimentally infected with Ostertagia ostertagi, is analysed using a mathematical model in which parasite fecundity is assumed to be an inverse function of both the duration and intensity of infection. The model incorporates a description of the frequency distribution of mature parasites between hosts (which is less over-dispersed than is usual for many other helminth infections). The model provides a good overall description of the decline in faecal egg production observed during trickle and single infection experiments. The main discrepancy between a comparison of the model predictions and the results of the most detailed available series of trickle infection experiments occurs at the initial peak of egg production. The magnitude of this difference appears to be related to the worm burden at the peak of egg production. The possible mechanisms underlying density-dependent regulation of the fecundity of O. ostertagia are discussed.

A mathematical model of the population biology of Ostertagia ostertagi is described. The model assumes that the natural control and regulation of parasite numbers is mediated by four processes: the effect of climate on the development and survival of the free-living stages; changes in the rate of establishment of the infective larvae, and density-dependent variations in parasite survival and fecundity. The model is used to compare the course of the infection in two groups of calves. One group is assumed to have been reared under conditions typical of S.E. England and the other under conditions typical of Louisiana, USA. The more general behaviour of the model is discussed in the context of sensitivity analysis. The model is an excellent mimic of the epidemiology of bovine ostertagiasis. It can be used as a simple screening procedure to help determine which of many possible anthelmintic control strategies should be selected for more detailed examination in the field, and it provides a theoretical framework within which ideas concerning the epidemiology of parasitic gastro-enteritis can be assessed and refined.

Five chemoprophylactic or chemotherapeutic strategies against bovine ostertagiasis are compared using a mathematical model of the population biology of Ostertagia ostertagi. The model offers a means of screening novel strategies prior to their further investigation in the field. Under conditions of climate and management typical of many regions in Northern temperate Europe, the model indicates that all of the tested prophylactic strategies will result in a profound reduction in the intensity of infection in grazing beef calves when compared with an untreated control group or the simple therapeutic protocol. Not all of those strategies which caused diminution in the scale of the midsummer rise in pasture larval contamination resulted in progressively less contaminated pastures in subsequent years. Moreover, the reproductive potential of the parasite is so great that the principal advantage of the ‘pasture cleaning’ effect that is the consequence of some protocols is not that the pasture may eventually be used to graze untreated calves but that the treated animals are subjected to a progressively smaller parasitic challenge with the concomitant pay-off in production gains.

Two major groups of heat-stable proteins have been purified by heat denaturation from homogenates of eggs of the potato-cyst nematodes Globodera rostochiensis and G. pallida. SDS-polyacrylamide gel electrophoresis of protein homogenates from 6 G. rostochiensis populations and 7 G. pallida populations revealed 2 bands specific for G. rostochiensis and 3 bands specific for G. pallida. Two-dimensional electrophoresis showed that the 2 bands specific for G. rostochiensis consisted of 2 polypeptides differing slightly in isoelectric point, as did one of the bands specific for G. pallida. Conventional antisera made against protein homogenates of either Globodera species showed a complete cross-reaction with the species-specific proteins. The perspectives of the differences in protein composition between G. rostochiensis and G. pallida, established in this study, for a quantitative differentiation of mixed field populations of the two Globodera species, involving monoclonal antibodies, are discussed.

Since the work of Dujardin (1845), attempts have been made to decipher acceptable divisions of the trematode groups at higher taxonomic levels, and yet there is still no generally accepted classification of the higher taxa of the Trematoda as there are for other groups of parasitic worms, such as the Monogenea, Cestoda, Nematoda and Acanthocephala. Why is it that workers with a wide knowledge of trematode systematics, such as Dollfus, Stunkard, Manter and especially Yamaguti, have felt unable or unwilling to comment in detail upon the phylogenetic relationships within the group at higher taxonomic levels? One of the main reasons for this state of affairs lies in the fact that, generally speaking, the group is not easily split into major subgroups by obvious, non-homoplasious morphological characters. Early attempts at division, based upon sucker arrangements, i.e. monostome, distome, amphistome and gasterostome, are not satisfactory, as distomes form the vast majority of the Digenea and both monostomes and amphistomes are certainly polyphyletic. In addition, the picture within the Digenea is complicated by the group's complex life-history patterns. Whereas early classifications all tended to be based upon adult (marital) morphology, life-history patterns are given great weight by workers such as Pearson (1972) and Bozhkov (1982). The cercarial morphology is considered the dominant feature in the classification of the group presented by La Rue (1957) and is emphasized in the phylogenetic relationships between the subgroups recognized by Cable (1974). Odening (1961), following an earlier suggestion of Lebour (1912), presented a classification, the major divisions of which were based upon the daughter-parthenita (i.e. the redia or daughter-sporocyst), a stance which he later found untenable (Odening, 1974). Consequently, the wealth of conflicting data from these and other sources has deterred the presentation both of classifications and speculations on evolutionary relationships. The classification of Odening (1974) and the recent cladistic analysis of Brooks, O'Grady & Glen (1985b) utilized data from all of the life-history stages. As the classification of Brooks et al. (1985b) is the most recent, and readily available in English, it must be a serious contender in terms of general acceptance. If it is accepted, then one would hope that this will be on its merits rather than because of its availability or the lack of viable alternatives; but, as discussed below, it is easy to find fault with this classification when it and its premises are examined in detail.