The risk factors associated with gametocytaemia at presentation and after treatment with different antimalarial drug regimens were evaluated in 767 children enrolled prospectively in 5 antimalarial drug trials between July 1996 and December 2002 in a hyperendemic area of southwestern Nigeria. The children were assigned to one of 6 treatment groups: chloroquine (CQ) only; pyrimethamine-sulfadoxine (PS) only; amodiaquine (AQ) only; CQ combined with chlorpheniramine (CQCP); or PS combined with CQ (CQPS) or AQ (AQPS). At enrolment, 115 (15%) of 767 children were gametocyte carriers. During follow-up, 15·6% of all patients (i.e. 120 patients) developed patent gametocytaemia, which in 85% (102 patients) had developed by day 7 following treatment. In a multiple regression model, 4 factors were found to be independent risk factors for the presence of gametocytaemia at enrolment: male gender (adjusted odds ratio [AOR]=0·55, 95% confidence interval [CI] 0·36–0·83, P=0·005), absence of fever (AOR=1·61, 95% CI 1·05–2·5, P=0·03), duration of illness >3 days (AOR=1·57, 95% CI 1·0–2·4, P=0·047), and asexual parasite densities less than 5000/μl (AOR=0·42, 95% CI 0·24–0·73, P=0·002). The presence of patent gametocytaemia at enrolment (AOR=0·04, 95% CI 0·02–0·07, P<0·001) and recrudescence of asexual parasites within 14 days were associated with the presence of gametocytaemia 7 or 14 days after enrolment (AOR=0·5, 95% CI 0·3–0·8, P=0·007). Delay in the time taken to clear the initial parasitaemia (>2 days) was associated with increased risk of subsequent gametocyte carriage. These findings may have implications for malaria control efforts in sub-Saharan Africa where control of the disease depends almost entirely on chemotherapy.

Parasitology publishes original papers on most aspects of pure and applied parasitology including biochemistry, molecular biology, immunology, genetics, physiology, epidemiology, ecology, chemotherapy and the control of parasitic infections, the application of new techniques, advances in the understanding of host–parasite relationships, theoretical studies and major systematic revisions. There is no minimum or maximum length for a paper but all manuscripts, including short ones, must be prepared in the standard format for this journal and any manuscript that is excessively long will be returned for shortening.

Infection with filarial nematodes produces a chronic, long-lasting illness with adult worms able to survive within human hosts for up to 15 years. A contributor to the longevity of these parasites is the presence of phosphorylcholine (PC) on components of the worms' molecular secretions (ES). PC on ES modulates host immune responses towards an anti-inflammatory phenotype thereby generating an environment favourable for parasite survival. PC is attached to nematode ES via a covalent association with carbohydrate, which, although well-documented in bacteria and fungi, is absent from humans, making it an ideal target for the development of novel drugs. In order to produce such drugs it is first necessary to understand the structure and synthesis of nematode PC-glycans. ES-62 is the major PC-ES-product of Acanthocheilonema viteae and is a homologue of PC-ES found in human filarial nematodes. We have studied the structure and biosynthesis of PC-glycans of ES-62 by a combination of pulse-chase experiments, experiments involving the use of inhibitors of each of intracellular trafficking, oligosaccharide processing and phospholipid biosynthesis and various forms of mass spectrometry. Our indications indicate that PC is transferred in the lumen of the medial Golgi to an N-type glycan consisting of a trimannosyl core with or without core fucosylation bearing between 1 and 4 N-acetyl glucosamine residues. The structure of the PC-N-glycans found in ES-62 appears to be conserved amongst filarial nematodes in that it has additionally been identified in Onchocerca volvulus and O. gibsoni. Also, similar structures have been found in non-filarial parasitic nematodes and in the free-living nematode Caenorhabditis elegans. Finally, PC has also been recently found attached to the carbohydrate moieties of nematode glycosphingolipids and the structure of these will also be considered.

Mitochondria of the malaria parasite Plasmodium falciparum are morphologically different between the asexual and sexual blood stages (gametocytes). In this paper recent findings of mitochondrial heterogeneity are reviewed based on their ultrastructural characteristics, metabolic activities and the differential expression of their genes in these 2 blood stages of the parasite. The existence of NADH dehydrogenase (complex I), succinate dehydrogenase (complex II), cytochrome c reductase (complex III) and cytochrome c oxidase (complex IV) suggests that the biochemically active electron transport system operates in this parasite. There is also an alternative electron transport branch pathway, including an anaerobic function of complex II. One of the functional roles of the mitochondrion in the parasite is the coordination of pyrimidine biosynthesis, the electron transport system and oxygen utilization via dihydroorotate dehydrogenase and coenzyme Q. Complete sets of genes encoding enzymes of the tricarboxylic acid cycle and the ATP synthase complex are predicted from P. falciparum genomics information. Other metabolic roles of this organelle include membrane potential maintenance, haem and coenzyme Q biosynthesis, and oxidative phosphorylation. Furthermore, the mitochondrion may be a chemotherapeutic target for antimalarial drug development. The antimalarial drug atovaquone targets the mitochondrion.

Isoenzyme-based studies have identified 3 taxa/species/‘phylogenetic complexes’ as agents of visceral leishmaniasis in Sudan: L. donovani, L. infantum and “L. archibaldi”. However, these observations remain controversial. A new chitinase gene phylogeny was constructed in which stocks of all 3 putative species isolated in Sudan formed a monophyletic clade. In order to construct a more robust classification of the L. donovani complex, a panel of 16 microsatellite markers was used to describe 39 stocks of these 3 species. All “L. donovani complex” stocks from Sudan were again found to form a single monophyletic clade. L. donovani ss stocks from India and Kenya were found to form 2 region-specific clades. The partial sequence of the glutamate oxaloacetate transaminase (GOT) gene of 17 L. donovani complex stocks was obtained. A single nucleotide polymorphism in the GOT gene appeared to underlie the isoenzyme classification. It was concluded that isoenzyme-based identification is unsafe for stocks isolated in L. donovani endemic areas and identified as L. infantum. It was also concluded that the name L. archibaldi is invalid and that only a single visceralizing species, Leishmania donovani, is found in East Africa.

The bacterial flora of the intestine plays an important role in the virulence caused by Entamoeba histolytica. Cysteine proteinase (CP), an amoebic virulence factor, plays a major role in host cell destruction. The mechanism of increased virulence following bacterial co-association is not understood. We studied CP of E. histolytica HM1:IMSS which was co-associated with Escherichia coli K12 strain pre-incubated with GalNAc or CP specific inhibitor E 64. Co-association of E. histolytica with bacteria enhanced CP activity 3·6-fold as assessed by azocasein assay and substrate gel electrophoresis showed bands at molecular weights of 28, 35 and 56 kDa. Northern and Western blot analysis showed increase in ehcp2 and ehcp5 gene expression. Trophozoites co-associated with E. coli showed greater cytotoxicity of BHK cells by a 51Cr release assay than trophozoites that had not been co-associated; this enhancement was abolished by E-64 treatment. The killing of BHK 21 targets by E. histolytica was characterized by DNA laddering which was not inhibited with E-64. GalNAc pre-incubation of trophozoites reduced cytotoxicity and DNA laddering, while E. coli co-associated E. histolytica showed smearing with faint laddering of BHK implicating both necrosis and apoptosis. Hence, bacterial co-association increases CP activity and CP gene expression and contributes to the necrosis of the target cell.

An analysis is presented of continuous data collected over 11 years based on 1902600 person/days of observation on the malaria experience of the people of Daraweesh, a village in eastern Sudan. Malaria transmission is hypo-endemic: the acquisition of clinical immunity with age is not as obvious as in more holo-endemic areas and malaria remained a problem in all age groups throughout the study. However, this population, who are of Fulani origin, showed a distinctly variable level of disease susceptibility. Thirty-two percent of the village never reported malaria symptoms or required malaria treatment while others experienced up to 8 clinical episodes over the 11 years of observation. Malaria incidence was clearly influenced by drought but much less obviously by rainfall. To what extent outbreak patterns are explicable in terms of anopheline factors, and to human immune factors, remains an interesting question for malaria modelling in this, and in other low transmission zones, such as the burgeoning urban areas of modern Africa.

Ticks and tick-borne diseases affect animal and human health worldwide and are the cause of significant economic losses. Approximately 10% of the currently known 867 tick species act as vectors of a broad range of pathogens of domestic animals and humans and are also responsible for damage directly due to their feeding behaviour. The most important tick species and the effects they cause are listed. The impact on the global economy is considered to be high and although some estimates are given, there is a lack of reliable data. The impact of ticks and tick-borne diseases on animal production and public health and their control are discussed.

Cryptosporidium parvum is a protozoan parasite that causes widespread diarrhoeal disease in humans and other animals and is responsible for large waterborne outbreaks of cryptosporidiosis. Unlike many organisms belonging to the phylum Apicomplexa, such as Plasmodium spp. and Toxoplasma gondii, there is no clinically proven drug treatment against this parasite. Aspects of the basic biology of C. parvum remain poorly understood, including a detailed knowledge of key metabolic pathways, its genome organization and organellar complement. Previous studies have proposed that C. parvum lacks a relic plastid organelle, or ‘apicoplast’, but that it may possess a mitochondrion. Here we characterize a mitochondrion-like organelle in C. parvum by (i) ultrastructural and morphological description (ii) localization of heterologous mitochondrial chaperonin antibody probes (iii) phylogenetic analysis of genes encoding mitochondrial transport proteins (iv) identification and analysis of mitochondrion-associated gene sequences. Our descriptive morphological analysis was performed by energy-filtering transmission electron microscopy (EFTEM) of C. hominis and C. parvum. The ‘mitochondrion-like’ organelle was characterized by labelling the structure with a heterologous mitochondrial chaperonin probe (hsp60) both in immunoelectron microscopy (IMEM) and immunofluorescence (IMF). Phylogenetic analysis of the mitochondrial import system and housekeeping components (hsp60 and hsp70-dnaK) suggested that the C. parvum mitochondrion-like organelle is likely to have descended from a common ancestral apicomplexan mitochondrion. We also identified a partial cDNA sequence coding for an alternative oxidase (AOX) gene, a component of the electron transport chain which can act as an alternative to the terminal mitochondrial respiratory complexes III and IV, which has not yet been reported in any other member of this phylum. Degenerate primers developed to identify selected mitochondrial genes failed to identify either cytochrome oxidase subunit I, or cytochrome b. Taken together, our data aim to provide new insights into the characterization of this Cryptosporidium organelle and a logical framework for future functional investigation.

Marteilia refringens is a paramyxean parasite which infects the flat oyster Ostrea edulis and mussels (Mytilus galloprovincialis), where it has been attributed to a separate species, Marteilia maurini, by several authors. Doubts persist though as to the existence or not of two species of Marteilia in Europe. We have devised a molecular method for the diagnosis of M. refringens based on 358 bp nested-PCR of the rDNA intergene spacer (rDNA IGS) which is capable of detecting 0·5 fg of M. refringens DNA. Molecular characterization of this spacer indicates that the Marteilia parasites which infect oysters and mussels are two different strains of the same species.

Malaria is a major health concern particularly in Africa which has about 90% of the worldwide annual clinical cases. The increasing number of drug-resistant Plasmodium falciparum justifies the search for new drugs in this field. Antimalarial activity of 2-substituted 6-nitro- and 6-amino-benzothiazoles and their anthranilic acids has been tested. An in vitro study has been performed on W2 and 3D7 strains of P. falciparum and on clinical isolates from malaria-infected patients. Toxicity has been assessed on THP1 human monocytic cells. For the most active drug candidates, the in vitro study was followed by in vivo assays on P. berghei-infected mice and by in vitro assays in order to determine the stage-dependency and the mechanism of action. Of 39 derivatives tested in vitro, 2 had specific antimalarial properties. Each compound was active on all stages of the parasite, but one was markedly active on mature schizonts, while the other was more active on young schizont forms. Both drugs were also active on mitochondrial membrane potential. In vivo data confirmed efficiency with a sustained decrease of parasitaemia. Products A12 and C7 may be considered as potential antimalarial worthy of further chemical and biological research.

Plasmodium falciparum gametocytes grown in vitro were fed through membrane feeders to laboratory-reared Anopheles stephensi mosquitoes. Intact midguts, including entire bloodmeal contents, were removed between 24 and 48 h post-bloodfeeding. Giemsa-stained histological sections were prepared from the midguts and examined by light microscopy. Contrary to previous reports, ookinetes were clearly visible within midgut epithelial cells, demonstrating intracellular migration across the midgut wall. Ookinetes entered epithelial cells through the lateral apical membrane at sites where 3 adjacent cells converged. There was no evidence for the existence of a morphologically distinct group of epithelial cells preferentially invaded by ookinetes. However, ookinete penetration was associated with significant morphological changes to invaded cells, including differential staining, condensation and fragmentation of the nucleus, vacuolization, loss of microvilli and various degrees of extrusion into the midgut lumen. Epithelial cells completely separated from the midgut wall were found within the midgut lumen. These cells were associated with invading parasites suggesting that ookinete penetration resulted in complete ejection of invaded cells from the midgut wall. Small clusters of morphologically altered midgut cells and invading parasites spanning the membranes of adjacent abnormal epithelial cells were observed, consistent with intracellular movement of ookinetes between neighbouring midgut cells. Extruded epithelial cells were also observed rarely in uninfected midguts. Epithelial cell extrusion, therefore, may be a general mechanism of tissue repair through which damaged cells are removed from the midgut wall rather than a parasite-specific response. These observations demonstrate that human malaria parasite infection of mosquitoes is consistent with, and provides further support for, the Time Bomb model of ookinete invasion of the mosquito midgut epithelium previously proposed for rodent malaria parasites.

The neuromuscular systems of parasitic helminths are targets that are particularly amenable for anthelmintics. In this study, we describe a GABAergic neurotransmission in adult Schistosoma mansoni, the trematode responsible for high levels of morbidity in people living in developing countries. GABA immunoreactivity (GABA-IR) was detected in nerve cells and fibres of the cerebral ganglia and longitudinal nerve cords and the nerve plexuses ramifying throughout the parenchyma of male adult worms. In addition, strong GABA-IR was also found associated with the oral and ventral suckers as well as in testes indicating a role for GABA in fixation to the host vascular wall and spermatogenesis. The capacity to synthesize GABA from glutamate was confirmed by measurement of a glutamate decarboxylase (GAD) activity. Supporting these data, a single band with an apparent molecular weight of about 67 kDa was detected using an antibody raised against mammalian GAD. In vivo studies revealed that picrotoxin, a non-competitive antagonist of the GABAA receptor, produced a modification of the motility and locomotory behaviour of adult worms, suggesting that GABAergic signalling pathway may play a physiological role in the motonervous system of S. mansoni and could be considered as a potential target for the development of new drugs.

Axenic trophozoites of Entamoeba histolytica strain HM1-IMSS grown in vitro in the presence of E-64, a potent irreversible inhibitor of cysteine proteinases, preserved their viability, their rate of replication, their resistance to complement, their haemolytic capacity and their ability to destroy target cells, despite complete inhibition of total cysteine proteinase activity. On the other hand, their erythrophagocytic capacity and their ability to decrease TER of MDCK cells was partially decreased. The same trophozoites injected into the portal vein of hamsters receiving a maintaining dose of E-64 failed to cause tissue damage and were rapidly eliminated. Our results suggest that amoebic cysteine proteinase activity is not required for amoebic functions in in vitro conditions, but that it becomes necessary for survival of trophozoites in in vivo conditions, whatever other role (if any) it may play in the parasite's virulence.

The mechanism by which Giardia lamblia exerts its pathogenicity is likely to be multifactorial. A 58 kDa enterotoxin was purified and characterized from the excretory–secretory product (ESP) of the parasite (Kaur et al. 2001). In the present study an attempt has been made to elucidate the mechanism of action of the ESP, a potentially important enterotoxin. A 41 kDa glycoprotein was identified in the mouse enterocyte membrane fraction with which the ESP interacted in a GM1-specific manner. The GTPase activity was reduced in enterocytes stimulated with the ESP, resulting in an increase in the level of adenylate cyclase-dependent cyclic adenosine monophosphate (cAMP). The activity of protein kinase A (PKA) in the enterocytes was also upregulated after ESP treatment. Ultimately, a significant increase in intracellular Ca2+ concentration and decrease in cytosolic Cl− level were noticed in ESP-stimulated mouse enterocytes. Thus it is possible that the enterotoxic ESP could bind to the 41 kDa glycoprotein (receptor?) on the enterocytes and activate the G-protein-mediated signal transduction pathway resulting in alteration of electrolyte transport.

This study reports the distribution of parasite genotypes for the trypanosome Crithidia bombi across individual units (the colonies) in host populations of a social insect, the bumble bee Bombus terrestris. A number of microsatellite primers were developed and several of them were found to be polymorphic in our samples. Furthermore, a simple algorithm was used to identify the likely multi-locus genotypes present in multiply infected host individuals. The results demonstrated a remarkably high degree of genetic diversity among infections. A first sample from 1997 could only use a low resolution with 2 loci and showed a total of 11 different genotypes of C. bombi from 12 colonies. The sample from 2000 was analysed at 6 polymorphic loci and contained data from 8 colonies that were infected by 27 different C. bombi genotypes. Roughly 16% of all individual bees but half of all colonies (2000 sample) were infected with more than 1 genotype. The infections in the different colonies were also genetically distinct from each other, and the parasite population as a whole was in linkage disequilibrium and deviated from Hardy–Weinberg expectations. The highly structured and genetically diversified population of C. bombi is likely to result from strong genotypic host–parasite interactions.

We present a new phylogenetic analysis of 15 primate Plasmodium species based on 18S rDNA sequences including new sequences of Plasmodium coatneyi, P. fieldi, P. gonderi, P. hylobati and P. simium. The results are discussed in the context of the parasite host species and their geographical distribution. Contrary to other phylogenies constructed with this 18S rDNA molecule, we observed that the topology of phylogenetic trees was not affected either by the quality of the nucleotide matrices, or by the species present in the outgroup. This analysis showed the following. (1) The polyphyly of human Plasmodium is confirmed. (2) The monophyly of Plasmodium from Old World monkeys is confirmed by the new added sequences and P. gonderi, an African species, possibly could be at the root of this group. (3) The most parsimonious biogeographical hypothesis is that P. vivax originated in Asia; thus, its related species P. simium appears to be derived through a transfer from the human P. vivax to New World monkey species in South America. (4) Sampling efforts of non-human primate Plasmodium could permit improvement of the knowledge of primate Plasmodium phylogeny and also consideration of the risks of malaria emergence from monkey reservoirs.

In recent years there has been much progress in our understanding of the phylogeny and evolution of ticks, in particular the hard ticks (Ixodidae). Indeed, a consensus about the phylogeny of the hard ticks has emerged which is quite different to the working hypothesis of 10 years ago. So that the classification reflects our knowledge of ticks, several changes to the nomenclature of ticks are imminent or have been made. One subfamily, the Hyalomminae, should be sunk, while another, the Bothriocrotoninae, has been created (Klompen, Dobson & Barker, 2002). Bothriocrotoninae, and its sole genus Bothriocroton, have been created to house an early-diverging (‘basal’) lineage of endemic Australian ticks that used to be in the genus Aponomma. The remaining species of the genus Aponomma have been moved to the genus Amblyomma. Thus, the name Aponomma is no longer a valid genus name. The genus Rhipicephalus is paraphyletic with respect to the genus Boophilus. Thus, the genus Boophilus has become a subgenus of the genus Rhipicephalus (Murrell & Barker, 2003). Knowledge of the phylogenetic relationships of ticks has also provided new insights into the evolution of ornateness and of their life cycles, and has allowed the historical zoogeography of ticks to be studied. Finally, we present a list of the 899 valid genus and species names of ticks as of February 2004.

During asexual development Plasmodium schizonts undergo a series of complex biochemical and structural changes. Using tightly synchronized cultures of 2 P. falciparum lines (clone C10 and strain ITO4) for light microscopy and fluorescence imaging we monitored the timing and sequence of expression of proteins associated with invasion-related organelles. Antibodies to rhoptry, micronemal and dense granule proteins (Rhoptry Associated Protein 1, Apical Membrane Antigen 1, Erythrocyte Binding Antigen 175, Ring-infected Erythrocyte Surface Antigen) and to pellicle-associated proteins (Merozoite Surface Protein 1, PfMyosin-A) were used. Clone C10 developed faster than ITO4; this difference was also found in the timing of protein expression seen by immunofluorescence. Light microscopic data were combined with transmission electron microscopic analysis using serial sectioning of ITO4 schizonts to determine nuclear number and organellar development. Thus a timetable of schizont structural maturation was established. Generally, the timing of organelle-specific antigen expression correlates well with the ultrastructural data. Rhoptries are formed mainly between second and fourth nuclear divisions, micronemes between the end of the fourth nuclear division and merozoite separation from the residual body, while dense granules are generated mainly after the micronemes. PfAMA-1 appears in micronemes before EBA-175, suggesting micronemal heterogeneity.