Glucose uptake was examined in adult specimens of Proterometra macrostoma (Trematoda: Digenea) recovered from the stomach (endoparasites) and gills (ectoparasites) of longear sunfish, Lepomis megalotis. The endoparasitic forms transported glucose directly through the external body surface by Na+-independent, facilitated diffusion, but the ectoparasites absorbed glucose by free diffusion alone. To determine how this transport function is regulated, cercariae were incubated in solutions having Na+ concentrations normally found in fish gut (50 mM) and in fresh water (0·5 mM). Glucose transport capacity was retained in 50 mM Na+, but disappeared in worms incubated for 1–3 days in 0·5 min Na+. Returning worms from the latter solution to one containing 50 mM Na+ fully restored glucose transport within a day. By contrast, incubation up to 5 days in 0·5 mM Na+ had no effect on glucose transport in endoparasitic adults of P. macrostoma and cercariae of P. edneyi. Thus, cutaneous sugar transport function in the migrating larva of P. macrostoma is subject to indirect regulation by environmental Na+.

Host specificity of a siphonostome copepod Ophiopsyllus reductus was confirmed by the results of an extensive survey of co-existing possible alternate host brittlestars. The parasite was found only on Ophiocomella ophiactoides. The ability to discriminate between potential hosts was tested experimentally. O. ophiactoides was always preferred and, in experiments with unrelated alternative hosts, the discrimination was absolute. When closely related species were the alternate host, discrimination was less complete. It is suggested that the discrimination is due to recognition of either tactile or chemical characteristics of the preferred host.

A monoclonal antibody-producing hybridoma cell line has been raised against merozoites of Babesia divergens. This antibody is strongly reactive against merozoites in an enzyme-linked immunosorbent assay (ELISA) and is also positive in an indirect fluorescent antibody test (IFAT) on preparations of live merozoites. The antibody recognizes an antigen, of molecular weight (Mr) 50–60 K by Western blot analysis on SDS–polyacrylamide gel electrophoresis (SDS–PAGE) gels. Merozoite neutralization assays show that the antibody significantly inhibits merozoite invasion of bovine erythrocytes.

Four monoclonal antibodies, raised against macroschizonts of Theileria parva, were studied to characterize their antigen binding specificity. The indirect fluorescent antibody test showed that the antigen(s) recognized were present in the macroschizont stage of the parasite life-cycle but not in piroplasm, kinete or sporozoite stages. Immunoblot analysis of macroschizont stage antigens suggested that all four antibodies recognized the same antigen. This was a molecule which varied in molecular mass between different parasite stocks, ranging from 68000 to 95000 Da. The antigen was localized by immunoelectron microscopy to the surface of the intracellular macroschizonts.

Isoenzyme analysis was used to characterize 6 species of trypanosomes of the subgenus Herpetosoma using 13 different enzyme systems. The species studied were Trypanosoma lewisi, T. musculi, T. grosi, T. microti, T. evotomys and T. nabiasi which cannot be distinguished on morphological grounds. Extracts for thin-layer starch-gel electrophoresis were prepared from cultures of insect forms in either Schneider's Drosophila or Grace's insect tissue culture media with foetal calf serum or a nutrient agar medium. Extracts of T. lewisi and T. musculi bloodstream forms were also run for comparison. All parasites gave distinct patterns which enabled them to be differentiated on one or more enzyme systems. Two types of computer analysis were used to group the parasites; using these techniques the murine parasites T. lewisi, T. musculi and T. grosi fell into one broad group, and T. microti and T. evotomys of microtine rodents formed another. These findings are in accord with earlier observations on the behavioural characteristics of these parasites in their mammalian host and their vector (fleas). The clear differences observed provide the basis for the application of other biochemical and immunological techniques for differentiation within this subgenus of trypanosomes.

Single percutaneous immunizations of Fischer rats with 1000 ultra-violet attenuated Schistosoma japonicum cercariae induced 52–88% resistance to challenge 4 weeks later. Increasing this to 3 immunizations induced 90% resistance to challenge, and this level of protection remained undiminished for up to 40 weeks after vaccination. Rats vaccinated with gamma-irradiated S. mansoni cercariae were resistant to challenge with S. mansoni but not S. japonicum. Similarly rats vaccinated with u.v.-attenuated S. japonicum cercariae were not resistant to heterologous challenge. Thus irradiated vaccines are species-specific in both permissive and non-permissive hosts.

Fischer rats infected with Fasciola hepatica showed significant resistance to Schistosoma mansoni challenge, and vice versa, whereas immunization with 20 Krad-irradiated S. mansoni cercariae failed to protect against F. hepatica challenge, but did protect against homologous challenge. When groups of rats received intraperitoneal implants of newly excysted juvenile flukes, 20- to 22-day-old juveniles, or 8- to 10-week-old flukes, none was significantly protected against S. mansoni challenge, whereas juvenile implants did protect against homologous F. hepatica challenge. In passive transfer experiments in rats, serum from F. hepatica-infected rats or rabbits protected recipients against homologous, but not heterologous challenge, and serum from rats vaccinated with 20 Krad-irradiated S. mansoni cercariae protected recipients against homologous, but not heterologous challenge. These experiments provide evidence that the mechanisms involved in homologous and heterologous resistance are different, the latter lacking immunological specificity. Microsphere injections in F. hepatica-infected rats demonstrated ‘shunting’ from the portal system to the systemic circulation. If migrating schistosomula are also ‘shunted’ in Fasciola-infected rats, this, rather than immunologically specific effector mechanisms, might explain their failure to establish in the portal system.

Alterations in the hepatic portal vasculature of NMRI mice infected with Schistosoma mansoni were assessed using a microsphere injection technique. The accumulation of eggs in the livers of infected mice and the development of portal hypertension were closely related to the worm pair burden during the first 15 weeks of infection. Individual variation between mice harbouring identical patent worm pair burdens was partially explained by the reduced fecundity of females from sexually biased infections. As eggs accumulated in the liver and portal hypertension increased, the number of injected microspheres escaping from the hepatic portal system rose in rank order of diameter from 9 μm through 15 μm and 25 μm to 50 μm. There was a strong correlation between the numbers of parasite eggs in the lungs and injected microspheres recovered from the lungs. The pattern of detection of microspheres in the lungs indicated a progressive increase in diameter of intra-hepatic porta-systemic connexions, followed by development of large-bore extra-hepatic collateral vessels. An accurate temporal profile of the pathological state of the host and the extent of collateral vessel formation was obtained. Injection of 141Ce-labelled microspheres demonstrated that the arterial supply to all organs of the body was affected by alterations in the micro-vasculature of the liver and lungs.

The development of resistance in mice to reinfection with Schistosoma mansoni was recorded during an early chronic infection, and compared with hepatic portal pathological and vascular changes. The latter were assessed using a microsphere injection technique. The degree of acquired resistance was directly dependent on the patent worm burden and the time post-infection. Strong correlations were noted between the development of resistance and the appearance of parasite eggs in the lungs and spleens of infected hosts. Weaker associations were present between resistance and other aspects of the disease pathology, such as portal hypertension and organ weights. The appearance of injected microspheres in the lungs and spleens correlated well with the appearance of eggs in those organs and with the development of resistance. The levels of resistance had risen and microspheres were detected in the lungs, before the development of major extra-hepatic, porta-systemic collateral vessels. It is concluded that intra-hepatic vascular alterations may be a causal factor in the development of resistance, preventing the sequestration of migrating schistosomula in the liver. It is estimated that as much as 70–75% of the recorded resistance can be attributed to this immunologically non-specific mechanism.

The inhibitory effect of niridazole on hydrogen production by metronidazole-resistant (CDC-85) and susceptible (Cl-NIH) Trichomonas vaginalis strains was investigated. The results show that niridazole is more effective than metronidazole in inhibiting hydrogen production by the resistant isolate. In CDC-85 aerobic inhibition requires a 4-fold increase in metronidazole concentration compared with that required anaerobically, but the corresponding factor for niridazole is only 1·5-fold. Reduction of the drug by a hydrogenosome-enriched preparation gave rise to a multiline electron spin resonance detectable signal, which is due to a nitrogen-centred radical.

A panel of immunologically and biochemically defined monoclonal antibody probes has been used in conjunction with immunocytochemical techniques to localize target antigens in sections of different life-cycle stages of Trichinella spiralis. Monoclonals that immunoprecipitate surface components from adult worms, show reactivity with the surface but not with internal tissues of sectioned parasites. Reagents that immunoprecipitate radio-isotope labelled stage-specific surface components of muscle-stage larvae, however, react with the stichosome and gut lining of sectioned larvae, as well as with the surface. Monoclonal antibody probes that do not stain the surfaces of live, intact muscle larvae in immunofluorescence assays, but which immunoprecipitate solubilized surface glycoproteins, also show reactivity with cuticular and stichosomal antigens of sectioned larvae. The more powerful resolution provided by electron microscopy has localized the surface antigens to the epicuticle and the intestinal antigens to the brush-border microvilli. Of particular interest was the finding that antigens of muscle-stage larvae, known to confer protection upon recipient mice, also exist in the stichosome of adult parasites. This observation may shed some light on the fact that mice immunized with antigens from muscle-stage larvae show, in addition to reduced muscle larva burden, accelerated expulsion of adult worms. The implications of these data for stage specificity of immune responses to trichinosis are discussed.

Anti-thymocyte serum (ATS) was administered to CD-1 mice infected with 100 Trichinella spiralis larvae and its effects on intestinal lysophospholipase (EC 3.1.1.5) activity, peripheral blood lymphocytes and bone marrow, peripheral blood and intestinal eosinophilia were assayed in the same experimental animal. The ATS caused a significant suppression of both the tissue lysophospholipase response and eosinophilia, in all three compartments, when compared to the values found in infected mice that were either treated with normal rabbit serum (NRS) or untreated. The suppressed eosinophil response and reduced lysophospholipase activity demonstrated a close temporal relation throughout the experiment. These findings support the hypothesis that helminth parasite-induced eosinophilia is the cause of increased lysophospholipase activity present in parasitized tissue and that the responses are thymus cell dependent.

The general structure and aspects of the development of the ovaries of the palaeacanthocephalan Corynosoma semerme were studied by transmission electron microscopy using worms varying in age from 18 to 90 h obtained from experimental primary infections in hydrocortisone-treated rats instead of seals, which serve as the natural definitive hosts. The observations can be interpreted to show that the immature ovaries become transformed relatively rapidly from cellular spheres to the more complex mature ovaries consisting of the supporting and oogonial syncytia and the germ-line cells. The supporting syncytium developed before the oogonial syncytium. The cytological appearance of ovaries from worms from rats was found to be similar to that of ovaries from mature worms of unknown age from naturally infected seals. Ecological evidence is considered to suggest that the rapid maturation of C. semerme in rats may also occur when the parasite becomes established in seals.

The effects of the phenothiazine, Stelazine, on Hymenolepis diminuta were investigated. The cestode was incubated for 10 min at 37 °C with 1 mM trifluoperazine, in the presence and absence of Ca2+. Assay of brush border enzymes showed that drug treatment lowered the activities of alkaline phosphatase, Ca2+-ATP'ase, 5′-nucleotidase and type 1 phosphodiesterase. This occurred in parallel with a significant reduction in tegumental protein. Under these conditions gross changes in ultrastructural appearance and cellular organization were observed. There was a lack of ordered microtriches and the distal cytoplasm was absent. Glycogen granules were scattered throughout the cytoplasm within the subtegumental layer. The connective tissue also appeared to be in some disarray. The effects of Stelazine appeared to be dependent on time and were significantly increased when Ca2+ was included in the incubation medium. Incubation with the less hydrophobic phenothiazine trifluoperazine sulphoxide had minimal effect on the integrity of the cestode. The results reported here support the premise that certain phenothiazines may be considered as potential cestocidal agents.

The cestodes Echinococcus granulosus, Taenia multiceps, T. pisiformis, T. hydatigena, Hymenolepis diminuta, Moniezia expansa and Anoplocephala perfoliata all produced substances that stimulated thymidine incorporation by whole blood lymphocyte cultures. This mitogenic activity was demonstrated in metacestode cyst fluids, live protoscoleces and scoleces, parasite culture supernatants, and extracts of adult parasites. T. multiceps metacestode cyst fluid mitogen adhered to, but would not pass through, cellulose dialysis tubing. This adherence was reduced or prevented by D-glucose and by proteins. The mitogen was weakly anionic. With Sephadex G75 gel filtration, its elution volume was greatly decreased when the elution buffer contained 0·5 M D-glucose. Mitogenic activity was protease resistant and could be separated by gel filtration from all the cyst fluid proteins.

An evaluation has been made of the biological and epidemiological parameters that determine the basic reproductive rates of Taenia hydatigena and T. ovis. These host-parasite systems are characterized by (i) no overcrowding in either host; (ii) no parasite-induced mortality of either host; (iii) no density-dependent constraint in the definitive host, but a strong, rapidly mobilized, short-acting immunity in the intermediate host and (iv) egg production which, in the natural environment, is high enough to prevent superinfection. It is considered that tapeworms with these characteristics are more stable to fluctuations in environmental conditions and to control measures such as dog dosing, than species which have a low egg production and infectivity such as Echinococcus granulosus. Reciprocal immunity exists between T. hydatigena and T. ovis in sheep. Exposure to T. hydatigena suppresses infection by T. ovis, but not by E. granulosus. This has important epidemiological consequences where these parasites co-exist.

It is shown that under the conditions that prevailed in New Zealand in the late 1950s, Taenia hydatigena was hyperendemic, the life-cycle being regulated by a density-dependent constraint in the form of acquired immunity, and T. ovis was rare. The control measures that caused Echinococcus granulosus, which was endemic at the time, to decline towards extinction reduced T. hydatigena and T. ovis to endemic status only. A non-linear integrodifferential equation model, which was previously linearized to describe the life-cycle of E. granulosus in dogs and sheep in New Zealand, is used to describe the life-cycles of T. hydatigena and T. ovis. The model is then used to compare and contrast the population dynamics of these three species. The model is used to demonstrate that the endemic steady state is structurally unstable, and may be asymptotically unstable to small perturbations. It is also shown that despite the lower infection pressure experienced by the intermediate host in the endemic state, the numbers of larvae in sheep may be higher than in the hyperendemic state. Finally it is shown that the partial success of the control measures against T. hydatigena may have caused an increase in the numbers and prevalence of T. ovis larvae in sheep due to the reciprocal immunity between the two species.