A field trial was conducted to evaluate the potential of the nematode-destroying fungus Duddingtonia flagrans to control free-living stages of horse strongyles. In late Spring 2 groups of horses (yearlings) with mixed infections of strongyles were allowed to contaminate 2 equal-sized pastures. One of the groups (F) received a daily dose of D. flagrans mixed in a feed supplement, while the other (C) received a similar amount of supplement without fungus. During a 3-month contamination period strongyle egg counts in faeces and number of infective strongyle larvae harvested from faecal cultures were determined. Grass samples were collected fortnightly. After the contamination period the yearlings were removed and 2 groups of young tracer foals (TF and TC) grazed the fungus and control pastures respectively for 4 weeks, housed for another 15 weeks and then killed to determine their worm burdens. The number of larvae in cultures from group TF was significantly lower than that in TC and herbage infectivity was reduced to a very low level on the pasture grazed by horses fed fungi. The number of Strongylus vulgaris and Strongylus edentatus larvae was also significantly lowered in group TF. Cyathostome larvae recovered from the mucosa of the ventral and dorsal colon and from the caecum were significantly lowered in group TF foals. Also, the number of strongyles found in the gut contents of group TF foals were significantly reduced in the dorsal colon, but numbers of worms in the ventral colon and in the caecum were similar to those of the controls.

Plasmodium falciparum-infected erythrocytes were treated with proteases (trypsin, chymotrypsin, pronase, or V8 protease) or iodinated and the effect of these treatments on the cytoadherent behaviour of the cells was determined. As previously observed, protease treatment reduced cytoadherence. However, it was also found that the P. falciparum-induced adhesin, pfalhesin, was not removed by protease treatment. Gelatin flotation experiments and scanning electron microscopical examination of the treated cells indicated that protease exposure resulted in changes in the knob structures on the cells, which are known to affect the adherent behaviour of the cells. Iodination was found to be an effective method of inactivating pfalhesin.

The attachment of Eimeria tenella to its target cells as an obligatory intracellular pathogen is essential for the development of disease. Previous reports have established that other intracellular protozoa parasites have either fibronectin, an adhesion protein, or fibronectin receptors, both of which are involved in the interaction with the host cells. In this current research, studies have been undertaken to visualize a surface component that may be involved in the attachment of E. tenella to host cells. For this purpose, monoclonal antibodies, both anti-chicken and anti-human fibronectin, and also anti-chicken integrin were used. Our results show a fibronectin-like molecule with an apparent molecular weight of 110 kDa in mature schizonts and microgametes. Staining with serum directed against chicken integrin revealed immunoreactivity within mature schizonts. Both the fibronectin-like molecule and the integrin may play an important role in the parasite stage-cell interaction and the promotion of parasite uptake.

Little is known about the effects of infection with Borrelia burgdorferi, the bacterium that causes Lyme disease, on its tick vectors. The purpose of this study was to determine the behavioural and ecological effects of infection by the bacterium in nymphal and adult black-legged (Ixodes scapularis) ticks. We found that the effects of infection were more pronounced in adults than in nymphs. Compared to uninfected adults, infected adults were less able to overcome physical obstacles, avoided vertical surfaces, were less active and quested at lower heights. Infected nymphs showed increased phototaxis and attraction to vertical surfaces. Infected nymphs also showed trends toward increased questing height and a greater tendency to overcome physical obstacles although these trends were not statistically significant. These altered behaviours in an infected tick may affect survival or pathogen transmission and may reflect kin selection in the bacterial pathogen.

The effects of sex, age of the human host, patency of asexual and sexual stages and seasonality on infectiousness of Plasmodium falciparum to mosquitoes were investigated in a rural village in southern Tanzania between 1992 and 1994. Villagers from randomized subgroups of households were surveyed for malaria parasites. Gametocyte and trophozoite prevalences were age dependent and fluctuated without any clear pattern of seasonality. A sample of 107 participants, selected to include an excess of gametocyte carriers, slept under bednets with holes cut into the sides for 3 weeks. A total of 3837 Anopheles gambiae s.l. and 5403 A. funestus recovered from these bednets, was examined for all oocysts 5–7 days after feeding or for oocysts less than 17·5 µn in diameter 2–3 days after feeding. Additional blood slides from participants were taken twice weekly. The 5–7 day oocyst rates were 12·1% in A. gambiae s.l. and 10·9% in A. funestus and 2–3 day rates were 3·6 and 4·9%, respectively. The higher rates using the former method were attributed to previous infection. There were strong correlations in the levels of infection in both vectors when they fed on the same hosts. However, patent gametocytaemia was only weakly associated with the development of oocysts in the mosquito. Infectiousness was not related to host age, sex, or the season.

The Eucoilid parasitoid Leptopilina boulardi is able to suppress its host Drosophila melanogaster immune reaction. Some strains, however, are non-immune suppressive to that host. Virus-like particles (VLPs) responsible for the immune suppressive ability were investigated in different strains of L, boulardi with histochemical and ultrastructural techniques. Membrane-bound particles containing vesicles were observed in the reservoir of the long gland and also in the egg canal of the ovipositor. These particles are homologous with the immune suppressive VLPs already described in the reservoir of L. heterotoma. Similarities were also observed with the L2 particles described previously around the chorion of the parasitoid egg after infestation. A weak positive DNA specific histochemical reaction was observed inside the reservoir and at the ultrastructural level. Feulgen-derived techniques demonstrated that the reaction was localized inside the particles. The morphology of the particles as well as the immune suppressive ability varied between strains. Two morphotypes of VLPs are described; the ‘Is’ morphotype (always observed in immune suppressive or Is strains) and the ‘NIs’ morphotype (observed in the non-immune suppressive or NIs strain). The hybrids between Is and NIs strains produce a third type of particle, the ‘His’morphotype with half-immune suppressive ability and intermediate morphology. The origin of the particles' immune suppressive activity against D. melanogaster is discussed within the scope of host specificity.

We investigated the blood-feeding behaviour of a natural population of the human-feeding mosquito Anopheles punctulatus in Iguruwe, Papua New Guinea. In particular we investigated the relationship between the mosquitoes' blood-feeding behaviour and their infection by the malaria parasites Plasmodium falciparum and P. vivax. Female mosquitoes were caught at 4 times of the night, the amount of blood they had obtained was measured and their status of infection was evaluated. Among uninfected mosquitoes the bloodmeal size steadily increased through the night, possibly because they were progressively less likely to be disturbed by human activity as the night drew on. Infected mosquitoes, on the other hand, tended to feed maximally at all times of the night. This suggests that infected mosquitoes were more tenacious in their blood-feeding behaviour, being either less readily disturbed during a bout of feeding (and thus feeding longer) or more likely to return to continue their feed following disturbance (and thus feeding several times). Either change would increase the parasites' rate of transmission. We conclude that in this natural situation the two species of malaria parasites modified the mosquitoes' behaviour with the effect of increasing their own transmission.

Intraperitoneal implantation of adult gravid females of the bovine filarial parasite, Setaria digitata in Mastomys coucha was found to induce microfilaraemia lasting for about 125 days. The microfilariae (mf) could be detected as early as 4 days postimplantation (p.i.) and peak levels of about 30 mf in 20 µl of blood were observed by 21 days. A significant positive correlation was found between mf density and the body weight of recipients pre-implantation. The implanted adult worms were generally viable only for less than 1 week. Implantation resulted in a significant decrease in total leucocytes and erythrocytes, induction of eosinophilia, splenomegaly and anti-erythrocyte autoantibodies. The microfilariae in circulation developed into 3rd-stage infective larvae (L3) when fed onto Aedes aegypti (refm, Liverpool strain). The mf in circulation were found to be eliminated by oral administration of diethylcarbamazine citrate, indicating the usefulness of this model for screening potential anti-microfilarial drugs. During the microfilaraemic phase, priming with tetanus toxoid (TT) resulted in significantly decreased production of anti-toxin levels indicating a state of generalized immunosuppression. Induction of antibodies to various fractionated antigenic components of adult parasites could be demonstrated by enzyme immunoassay (EIA) in M. coucha implanted with live or cold-stunned adult worms. The S. digitata–M. coucha model thus is found amenable to perform chemotherapeutic and immunobiological investigations in experimental filariasis.

All the classical transmitter ligand molecules evolved at least 1000 million years ago. With the possible exception of the Porifera and coelenterates (Cnidaria), they occur in all the remaining phyla. All transmitters have evolved the ability to activate a range of ion channels, resulting in excitation, inhibition and biphasic or multiphasic responses. All transmitters can be synthesised in all three basic types of neurones, i.e. sensory, interneurone and motoneurone. However their relative importance as sensory, interneurone or motor transmitters varies widely between the phyla. It is likely that all neurons contain more than one type of releasable molecule, often a combination of a classical transmitter and a neuroactive peptide. Second messengers, i.e. G proteins and phospholipase C systems, appeared early in evolution and occur in all phyla that have been investigated. Although the evidence is incomplete, it is likely that all the classical transmitter receptor subtypes identified in mammals, also occur throughout the phyla. The invertebrate receptors so far cloned show some interesting homologies both between those from different invertebrate phyla and with mammalian receptors. This indicates that many of the basic receptor subtypes, including benzodiazepine subunits, evolved at an early period, probably at least 800 million years ago. Overall, the evidence stresses the similarity between the major phyla rather than their differences, supporting a common origin from primitive helminth stock.

Murine monoclonal and polyclonal antisera, raised against the 38 kDa subunit of Echinococcus granulosus antigen 5, were used to investigate the tissue distribution of the antigen in hydatid cysts. Immunoreactivity was visualized by indirect immunofluorescence on whole protoscoleces, and ultrastructural immunocytochemistry utilizing colloidal gold-based labelling procedures on unsectioned and cryosectioned brood capsules and protoscoleces. In protoscoleces, the 38 kDa subunit of antigen 5 was localized at the interface of parenchymal cells and associated extracellular matrices, as well as along the interface of the tegumentary syncytium in the somal region and its basal matrix. Cytoplasmic labelling of parenchymal cells was rare; when observed, it was associated with vesicles and membranes in cytoplasmic extensions of parenchymal cells. In brood capsules, the antigen was associated with the external face of the plasma of degenerating parenchymal cells. The 38 kDa subunit occurs along the extracellular face of cell membranes, suggesting that antigen 5 is either a component of the membranes or associated extracellular matrices.

Random amplified polymorphic DNA markers (RAPD) were used to visualize the genetic diversity within and between infrapopulations of Schistosoma mansoni recovered from the natural vertebrate host, Rattus rattus, trapped at an insular Guadeloupean focus. Phenotypes were characterized by the sex of the parasites and by 8 polymorphic markers generated by 3 primers. Among the 212 parasite individuals recovered from 10 infected rats, 78 genotypes were characterized. All the hosts naturally infected harboured multiple parasite genotypes with a maximum diversity of 28 genotypes/host. Phenotypic and genotypic diversity calculated by Shannon-Wiener's indices and Lynch and Milligan's estimators respectively is, on average, greater within than between hosts. Considering the very low snail infection rates observed in this focus and the rapid turnover of the vertebrate hosts, our results suggest that the high mobility of the vertebrate host and/or plurimiracidial snail infections could be factors responsible for parasite genetic diversity within hosts.

The effect of haemoparasites on the physiology and behaviour traits of their hosts was examined using Haemogregarina sp., a parasite of the common lizard, Lacerta vivipara, from the south of France. Infection with haemogregarines was associated with a reduced haemoglobin concentration and an increased number of immature red blood cells. Parasitized individuals also showed a reduced oxygen consumption at rest and a lower locomotor speed. We also found that the multiplication rate of the parasite depended on the temperature at which the lizard was maintained. Between 21 and 28 °C the multiplication rate of the parasite was significantly lower than between 29 and 35 °C. This suggests that the parasites may suffer reproductive costs when hosts reduce their body temperature.

The balanced polymorphism of glucose-6-phosphate dehydrogenase deficiency (G6PD-) is believed to have evolved through the selective pressure of malaria combined with consumption of fava beans. The implicated fava bean constituents are the hydroxypyrimidine glucosides vicine and convicine, which upon hydrolysis of their β-O-glucosidic bond, become potent pro-oxidants. In this work we show that the glucosides inhibit the growth of Plasmodium falciparum, increase the hexose-monophosphate shunt activity and the phagocytosis of malaria-infected erythrocytes. These activities are exacerbated in the presence of β-glucosidase, implicating their pro-oxidant aglycones in the toxic effect, and are more pronounced in infected G6PD- erythrocytes. These results suggest that G6PD- infected erythrocytes are more susceptible to phagocytic cells, and that fava bean pro-oxidants are more efficiently suppressing parasite propagation in G6PD- erythrocytes, either by directly affecting parasite growth, or by means of enhanced phagocytic elimination of infected cells. The present findings could account for the relative resistance of G6PD- bearers to falciparum malaria, and establish a link between dietary habits and malaria in the selection of the G6PD- genotype.

Recombinant Schistosoma mansoni elastase was expressed in Escherichia coli and an antiserum raised against the re-combinant protein was used to investigate stage-specific control of elastase in the parasite, and to determine whether the enzyme could form the basis of a strategy to prevent larval invasion of the host. Results showed that the expression of elastase is developmentally regulated, even if the basal promoter activity does not seem to be stage specific. The analysis of mRNA expression showed the presence of elastase transcript in adult worms although we could not detect the protein at this stage, suggesting that S. mansoni employs a form of translational control. The measurement of elastase levels in supernatants of culture schistosomula combined with the localization of elastase in cercariae invading mouse skin showed that the enzyme is heavily released during penetration. Finally, we studied the cytotoxic activity of rat anti-elastase sera, and the analysis of the isotypic profile suggested that IgG2a anti-elastase may be responsible for the cytotoxic effect.

Encapsulation of the benzimidazole albendazole in multilamellar liposomes results in a preparation in which this normally insoluble anti-hydatid drug is well solublilized in aqueous media. The high entrapment efficiency observed (75–87%) and the stability of the formulation make this a promising delivery vehicle for improved chemotherapy with albendazole. In particular, the high degree of association with phospholipid may give rise to increased oral bioavailability. Oral adminisration of albendazole in liposomes led to increased concentration and/or altered metabolism of albendazole sulphoxide (ABZSX) in liver and/or plasma in non-infected Wistar rats. Results from experiments using cotton rats (Sigmodon hispidus) infected with metacestodes of Echinococcus multilocularis show that entrapment within liposomes clearly increases the uptake of albendazole via the oral route. This was reflected by increased levels of albendazole and the two major metabolites in plasma, liver and cyst homogenate when a dose of liposomal albendazole (35 mg/kg) was given orally compared to free albendazole at 50 mg/kg. There was a 75–94% reduction in biomass of the metacestode and a significant increase in survival time for the animals treated with liposome entrapped albendazole. A clear difference in distribution of albendazole and its metabolites in the liver and the metacestode tissues in the presence of cimetidine indicated that the latter has a profound effect on the metabolism of albendazole. There appeared to be a synergistic interaction between albendazole and cimetidine, since the metabolism of albendazole was markedly altered in the combined cimetidine/liposome–albendazole group, and higher therapeutic effect was observed. These findings indicate potential both for improvement of treatment of larval E. multilocularis infection and for reduction of albendazole dose levels.

We have isolated and sequenced cDNA clones from Eimeria tenella and Eimeria maxima which encode proteins that share homology with a recently described family of calmodulin-domain protein kinases. The primary sequence data show that each of the protein kinases can be divided into 2 main functional domains – an amino-terminal catalytic domain typical of serine/threonine protein kinases and a carboxy-terminal domain homologous to calmodulin, which is capable of binding calcium ions at 4 ‘EF-hand’ motifs. Expression of the E. tenella calmodulin-domain protein kinase (EtCDPK) increased towards the end of oocyst sporulation, as judged by Northern and Western blotting, and indirect immunofluorescent antibody labelling showed that within a few minutes of adding sporozoites to target host cells in in vitro culture EtCDPK was found to be specifically associated with a filament-like structure that converges at the apical end of the parasite. Once the parasite entered the host cell EtCDPK appeared to be left on the host cell membrane at the point of entry, indicating a brief yet specific role for this molecule in the invasion of host cells by E. tenella.

A descriptive analysis of observed water contact activities in seven Kenyan (Akamba) communities is presented. The patterns of contact with time of day, month of year, type of activity, degree of immersion, use of soap, use of ‘kithima’ and day of week are all considered, with particular attention given to how these vary with age and sex. It is noted that (a) patterns of contact vary dramatically between these culturally rather similar communities, (b) contact usually peaks in the second decade of life, (c) generally females, especially young women, spend more time at the water than males and (d) simple (unweighted) total observed duration of contact gives a relatively inflated estimate of exposure in adults, especially young women. The methodology of observation and data handling is described in some detail.

Neuropeptides are ubiquitous signalling molecules in all metazoans possessing nervous systems, from the simple nerve nets of the cnidarians to the immensely complex systems of mammals. While the discipline of peptide neuroendocrinology was born through the study of higher vertebrates, there now exists a plethora of information regarding neuropeptides and peptidic regulatory factors in invertebrates. Such phylogenetic studies have revealed that peptidic neurotransmission is of early evolutionary origin and that, while invertebrates have nervous systems which are simpler in terms of nerve cell number and organisation when compared with vertebrates, the complexity of the peptidic ‘vocabulary’ of invertebrate neurones is of a similar order of magnitude. Most research on invertebrate neuropeptides has been directed towards representative members of groups such as the insects and molluscs and it is only in recent years that efforts have been focused on the helminths (platyhelminths and nematodes). Here, the putative origins of peptidic transmitters is discussed and the current state of knowledge on helminth neuropeptides is reviewed. In order to place the study of helminth neuropeptides in an historical and conceptual perspective, methodological development and conceptual modifications in the disciplines of vertebrate and higher invertebrate peptide neuroendocrinology have been summarised.

A low molecular weight factor in a basal medium essential for erythrocytic Plasmodium falciparum development in a serum-free medium using a cell growth-promoting factor derived from adult bovine serum was detected. The factor was hypoxanthine. The optimal hypoxanthine concentration for parasite growth was between 15 and 120 μM. The contribution of hypoxanthine to increased parasite growth was clearly evident in cultures on day 4. Among various low molecular weight supplements tested, adenine, adenosine, AMP, ATP, cyclic AMP, guanine, guanosine, inosine, inosine mono-phosphate, xanthine, NAD, NADH, NADP, NADPH and deoxyguanosine triphosphate showed a similar effect to that of hypoxanthine in the serum-free culture system. On the other hand, the addition of uric acid, FAD, thymidine, uridine, orotic acid, deoxythymidine triphosphate, deoxycytidine triphosphate, deoxyadenosine triphosphate, ribose-1-phosphate, or ethanolamine was not beneficial to the parasite growth. The results presented here will not only be of practical value, but will provide important information about the developmental requirements of the parasite.