Cytoadherence of Plasmodium falciparum-infected erythrocytes plays an important role in the pathogenesis of cerebral malaria. The identity of cell surface molecules on parasitized erythrocytes involved in cytoadherence is of great interest to understand the molecular basis of this mechanism. Peptide sequences derived from exofacial loops of the erythrocyte antigen band 3 from parasitized erythrocytes have previously been shown to inhibit cytoadherence. We now report that a non-repeated region of Pf155/RESA (residues 213–218) contains a hexapeptide motif being highly homologous to cytoadherence inhibitory sequences from band 3. Synthetic peptides containing the hexapeptide motif of Pf155/RESA inhibited the binding of P.falciparum-infected erythrocytes to melanoma cells in vitro. Furthermore, individuals residing in malaria-endemic areas have antibodies reactive with epitopes involving these motifs in band 3 and in Pf155/RESA.

Progarnia archosauriae nov. gen., nov. sp. (Haemosporina: Garniidae) is described in the blood of the South American caiman, Caiman crocodilus crocodilus (Archosauria: Crocodilia). The parasite undergoes merogony and gametogony principally in leucocytes and thrombocytes, but also invades erythrocytes in which it produces no ‘malarial’ pigment. It thus shares features of Fallisia and Garnia which are, respectively, intra-leucocytic and intra-erythrocytic haemosporines of the family Garniidae in present-day lizards. This, and the antiquity of the order Crocodilia, suggests that it was from such a parasite that the existing reptilian and avian haemosporines evolved. An overall evolutionary pattern is suggested.

The current taxonomy of parasites in the genus Sarcocystis is largely based on morphological characteristics as well as on host specificity and life-cycle structure. Recently, phylogenetic analyses of partial ribosomal RNA (rRNA) sequences provided support for paraphyly of Sarcocystis. We have tested the validity of this hypothesis by sequencing the complete 18S rRNA genes of Sarcocystis arieticanis, Sarcocystis gigantea and Sarcocystis tenella and comparing them with gene sequences derived from other taxa of the phylum Apicomplexa. The results obtained from this study do not reject the hypothesis of monophyly of Sarcocystis species, although the bootstrap data were inconclusive for some species.

An open randomized study was carried out to assess the efficacy of diethylcarbamazine (DEC) and mebendazole (MBZ) across, respectively, 39 and 41 patients, all exhibiting clinical and biological features evocative of toxocariasis, together with a positive immunodiagnosis by Western blot using Toxocara larvae excretory-secretory antigens. Clinical impact of the disease was quantified by a score system (20 parameters). Post-treatment follow-up used also results from eosinophil counts from total and specific anti-Toxocara IgE quantitations, and from Western blots. All patients attended the control check-up 1 month after the end of treatment. Analysis of the results showed a similar good efficacy of DEC and MBZ on clinical score and eosinophil count that were significantly lowered. MBZ therapy was slightly more efficient on specific anti-Toxocara IgE kinetics, while total IgE mean titres were not affected by either DEC or MBZ treatment. Patients from the DEC group reported a significantly higher rate of adverse reactions, most of which could be due to parasite lysis. This fact could be a strong argument for treating human toxocariasis with MBZ.

The seroprevalence of toxocariasis was investigated in 2129 school children ranging in age from 4 to 19 years. Infection, as measured by titre, was found to be high compared to values obtained from children in other countries, with 31% having a titre of ≥ 1:50 and 3·1% having titres of ≥ 1:800. Relalionships between seroprevalence and host factors including age, sex and location, and risk factors including geophagia, thumbsucking and pet ownership were explored. Age was found to be a significant factor in relation to infeclion with Toxocara. Males were significantly more infected than females, as were the inhabitants of rural schools versus urban schools. The percentage of seropositive children varied widely from school to school. Geophagia and pet ownership were found to be significantly associated with toxocariasis. Logistic regression analysis was used to model the relative contribution of these factors to infection wilh Toxocara. While this analysis identified factors which were highly significantly associated with Toxocara titre, the odds ratios were generally low indicating ihe low specificity of the model.

Following cell invasion, Trypanosoma cruzi trypomastigotes transform into amastigotes, which are the mammalian replicative forms of the parasite. Although amastigotes represent a critical stage in the life-cycle of T. cruzi, little is known of the factors controlling trypomastigote to amastigote transformation. Kanbera et al. (1990) observed that exposure of trypomastigotes to acidic pH induced their transformation into rounded forms resembling amastigotes. We confirm their observation and, using two strains of T. cruzi, establish that these transformants are ultrastructurally and biochemically indistinguishable from natural amastigotes. Incubation of trypomastigotes in medium at pH 5·0 for 2 h was sufficient to trigger their transformation into forms resembling amastigotes. Electron microscopical analysis confirmed that the kinetoplast structure, and general morphological features of the acid-induced, extracellular amastigotes were indistinguishable from those of intracellular-derived amastigotes. The extracellular transformation was accompanied by the acquisition of the stage-specific surface antigen of the naturally transformed amastigotes (Ssp-4), and loss of a stagespecific trypomastigote antigen (Ssp-3). Trypomastigotes incubated at neutral pH did not transform into amastigotes, and did not acquire the Ssp-4 epitope or lose the Ssp-3 epitope. Finally, acid-induced amastigotes subsequently incorporated [3H]thymidine into their DNA, indicating that the important replicative property of intracellular amastigotes is also exhibited by these in vitro transformants. This effect of low pH appears to be of physiological relevance, and acid-induced extracellular transformation appears to represent a valid experimental technique for studies of the molecular mechanisms involved in the differentiation process.

The proteolytic activities present in adult Necator americanus excretory–secretory products have been assessed using biologically relevant, naturally occurring substrates (haemoglobin and fibrinogen) and a number of synthetic fluorogenic and chromogenic substrates. One broad peak of activity was observed against haemoglobin in the pH range 5 to 7, with maximum activity at pH 6·6, while fibrinogenolytic activity was shown to be greater at pH 3·5. Inhibition studies against haemoglobin, fibrinogen and synthetic substrates using a battery of appropriate protease inhibitors indicated the presence of a mixture of aspartyl, cysteinyl and serine proteases. Metal ion (Ca2+, Zn2+ and Fe2+) stimulation was demonstrated, with stimulation by Zn2+ being the most marked. These results are discussed in the context of recent developments in the field of parasite proteolytic enzymes, where they have been suggested as targets for immuno- and chemotherapy.

Aspects of vitellogenesis, known to be controlled by juvenile hormone, are adversely affected by Hymenolepis diminuta infection of Tenebrio molitor, in spite of circulating titres of the hormone remaining unchanged. It has therefore been proposed that juvenile hormone binding is disrupted at the tissue site level. Juvenile hormone III binding sites were located in the nuclear, microsomal and post-microsomal supernatant fractions of the follicle cells of Tenebrio molitor. When JH-III binding was quantified for both control and Hymenolepis diminuta-infected beetles, binding in the nucleus and cytosol were found to be largely unaffected. However, microsomal binding was severely disrupted; on days 3 and 6 post-infection, binding was greatly diminished, on day 9 post-infection, binding was slightly reduced and, by day 15, binding was ‘restored’ to that of control insects. Using follicle cell microsomes at day 3 post-infection, previous Scatchard analysis revealed the presence of at least two JH-III binding sites. The first is of higher affinity, Kd = 5·3 x 10·5 x 10−11 mol/mg protein and the second of lower affinity Kd = 7·7 x 10−7 M, Bmax = 9·75 x 10−11 mol/mg protein. A comparison with microsomal binding parameters of follicle cells from non-infected Tenebrio indicated that although the Bmax values were unchanged, the Kd value of the higher affinity site was increased by approximately 5-fold. These data are indicative of a parasite-induced competitive binding inhibitor.

Faecal samples were taken in 2 consecutive years from Scottish Blackface lambs on a commercial farm in central Scotland to examine variation among lambs in the number of nematode eggs in their faeces. Samples were taken at intervals of 4 weeks from 1 to 5 months of age. Lambs were treated with a broad-spectrum anthelmintic at each sample date. Ewes and lambs were naturally infected by grazing pasture contaminated with mixed, predominantly Ostertagia circumcincta, nematode species. The ewes were removed from the lambs when the lambs were three months old. Only 3 of the 6 sets of samples taken prior to removal of the ewes fitted a negative binomial distribution but all sets of samples taken after this did so. The mean and the variance differed with the month and year of sampling. The amount of variation among lambs increased as the lambs grew from 3 to 5 months of age, possibly because of heterogeneity in the rate of development of protective responses. Counts taken in August and September, when the lambs were 4 and 5 months of age, were positively correlated with each other. In contrast, counts taken at 1 or 2 months of age were negatively correlated with counts taken when the lambs were 3–5 months old. Sex, date of birth, sire and dam were all associated with variation in faecal egg counts but the size and significance of their influence was dependent upon the date when faecal samples were taken. Four factors: sire, dam, sex and year accounted for over two-thirds of the variation among older lambs in faecal egg counts.

Studies of foraging strategies are often complicated by competing goals of the forager. In contrast, non-feeding infective juvenile entomopathogenic nematodes forage exclusively for a single host. Two questions were posed: (1) what is the relationship between metabolic rate, energy reserves and foraging strategy and (2) when a foraging strategy fails, will an infective-stage parasite switch strategies? Three species of entomopathogenic nematodes were stored in water and changes in their behaviour, metabolic rate, energy reserves, and infectivity were measured throughout the storage period. Steinernema carpocapsae ambushes insect hosts, whereas S. glaseri and Heterorhabditis bacteriophora cruise forage. Steinernema carpocapsae was least active and had the lowest metabolic rate. Heterorhabditis bacteriophora was more active and had the highest metabolic rate. Steinernema glaseri was most active and had an intermediate metabolic rate. Neither cruising species changed foraging strategy. Steinernema carpocapsae decreased nictation (a behaviour associated with ambushing only) and increased their locomotory rate. Any change in searching strategy occurred without assessment of the profitability or distribution of potential hosts, but the advantage this confers is unknown.

Parasite modification of host behaviour influences a number of critical responses, but little is known about the effects on host spatial abilities. This study examined the effects of infection with the intestinal trichostrongylid nematode, Heligmosomoides polygyrus, on spatial water maze learning by male laboratory mice, Mus musculus. In this task individual mice had to learn the spatial location of a submerged hidden platform using extramaze visual cues. Determinations of spatial performance were made on day 19 post-infection with mice that had been administered either 50 or 200 infective larvae of H. polygyrus. The infected mice displayed over 1 day of testing (6 blocks of 4 trials) significantly poorer acquisition and retention of the water maze task than either sham-infected or control mice, with mice that had received 200 infective larvae displaying significantly poorer spatial performance than individuals receiving 50 larvae. The decrease in spatial learning occurred in the absence of either any symptoms of illness and malaise, or any evident motor, visual and motivational impairments. It is suggested that in this single host system the parasitic infection-induced decrease in spatial learning arises as a side-effect of the host's immunological and neuromodulatory responses and represents a fitness cost of response to infection.

The objectives of this study were (1) to determine the impact of severe zinc deficiency on the establishment, growth, survival and reproduction of Heligmosomoides polygyrus in the laboratory mouse, during both primary and challenge infection protocols, and (2) to determine whether the observed effects resulted from zinc deficiency per se, or from the accompanying energy restriction. Three diet groups were used: zinc-sufficient (Zn+: 60 mg zinc/kg diet), zinc-deficient (Zn·75 mg zinc/kg diet) and energy restricted (ER: 60 mg zinc/kg diet pair fed to Zn− mice). Neither Zn− nor ER influenced the establishment of the parasite during a primary infection. However, both significantly influenced the early development of the parasite. The proportion of adult worms recovered 9 days post-infection (p.i.) was highest in Zn− mice, intermediate in ER mice and lowest in +Zn+ mice. Worms were also distributed more distally in the intestine of the Zn− mice and worm survival was highest in Zn− mice, intermediate in ER mice and lowest in Zn+ mice at both 4 and 5 weeks p.i. Although the length of female worms was reduced in Zn− mice, neither per capita fecundity nor egg viability was affected by zinc deficiency. Energy restriction, on the other hand, significantly reduced worm fecundity at 5 weeks post-primary infection, but had no effect on egg viability. Zinc concentration of adult H. polygyrus was similar among dietary groups. The effects of zinc deficiency and energy restriction were also investigated 4 and 5 weeks after a challenge infection. Whereas strong host resistance was evident in Zn+ and ER mice, based on comparison of worm numbers between challenged mice and primary infection controls, no evidence of resistance was detected in Zn− mice. As in the primary infection, female worms were shorter in Zn− mice than in ER and Zn+ mice, and energy restriction but not zinc deficiency significantly affected per capita fecundity. However, in contrast to the primary infection, ER mice had elevated rather than reduced fecundity. This study demonstrates a complex interaction between H. polygyrus and zinc and energy restriction, and highlights the importance of controlling for reduced food intake in nutrition–infection studies.

There is a general lack of basic information concerning one class of glycoconjugate, the glycolipids, from parasitic nematodes. As the prototype, the neutral glycolipid fraction derived from adult males of Ascaris suum was investigated as to its chromatographic, differential chemical staining, antigenic and chemical properties. The thin-layer chromato-graphy-resolved neutral fraction glycolipids could be classified into components of fast and slow migrating band groups. Immunoreactivity was restricted to the latter as detected by IgG and IgM anti-neutral fraction glycolipid antibody levels in serial infection sera of mice. Similarities of chromatography, antigenicity and serological cross-reactivity have been extended to the neutral glycolipid fractions of other parasitic nematodes: Litomosoides carinii and Nippostrongylus brasiliensis. Chemical, differential chemical staining and enzymatic analyses identified the Ascaris suum antigenic, slow migrating band group of components as amphoteric glycosphingolipids, and not the originally hypothesized glyco-glycerolipids or glycosylphosphatidylinositols, that contained typical neutral monosaccharide constituents and a zwitter-ionic phosphodiester linkage, most probably phosphocholine. Glycosphingolipid-immunoreactivity is eliminated on cleavage of the zwitterionic phosphodiester linkage by hydrofluoric acid treatment.

NADPH diaphorase has recently been discovered to be responsible for neuronal nitric oxide (NO) synthase activity in mammals. It thus serves as a histochemical marker for the localization of NO synthase in the nervous system. The histochemical technique was used to map out potential NO-producing neurones in the nervous system of the parasitic nematode, Ascaris suum. Positive staining for NADPH diaphorase was present in various parts of the central nervous system, in particular within selective cell bodies and fibres in the ventral ganglion, the retrovesicular ganglion, ventral and dorsal cords and sublateral lines. Intense staining was also present in the motorneurone commissures, indicating a potential role for NO as a neurotransmitter at the neuromuscular junction. NADPH disphorase-positive neurones were not confined to the central nervous system. Selective staining was also present in the enteric nervous system, in particular the pharynx and in the peripheral nervous system innervating the sensory organs.