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.

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.

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 ‘Muguga cocktail’ live vaccine comprises three Theileria parva stocks (Muguga, Kiambu 5 and the buffalo-derived Serengeti-transformed) and has been used extensively in Eastern, Central and Southern Africa with an infection and treatment protocol to protect cattle against East Coast fever. We report the characterization of the three component vaccine stocks using a panel of polymorphic micro-satellite and mini-satellite markers and the development of a stock-derived PCR method that distinguishes two of the vaccine stocks. These markers, with the use of a recently developed Reverse Line Blot assay, have enabled us to address four important questions in relation to vaccination. First, how closely related are the vaccine stocks, secondly do all three stocks persist post-vaccination and induce a carrier state, thirdly is there evidence for the transmission of the vaccine stocks and fourthly does vaccination prevent infection with local genotypes? The results show that Muguga and Serengeti-transformed stocks are highly related but very distinct from Kiambu 5 that persists in vaccinated cattle establishing a carrier state. No evidence was obtained for the transmission of vaccine stocks to co-grazed animals, although these animals were infected with up to 8 different T. parva genotypes showing there was a significant level of tick challenge. Some of the vaccinated animals become infected with a subset of local genotypes providing evidence for limited vaccine ‘breakthrough’.

This paper investigates a cohort of 2187 laboratory reared Culex quinquefasciatus fed on 69 human volunteers, including 59 persons with different levels of Wuchereria bancrofti microfilariae and 10 without microfilaria. Mosquitoes were followed until death. Mosquito survival was analysed in relation to the level of microfilaria in the human and larval count in the dead mosquito. Vector mortality during the extrinsic incubation period (12 days post-engorgement) was significantly higher in mosquitoes fed on microfilaraemic volunteers (50%) than in those fed on amicrofilaraemics (29%). Both the percentage infected and the geometric mean parasite density was significantly higher among mosquitoes which died before 13 days (45% infected and 10 larvae per infected mosquito) than those surviving beyond 13 days (39% and 2·2), suggesting a parasite loss of more than 80% during the extrinsic incubation period. A large proportion (62%) of the mosquitoes that died during the early of phase of parasite development were infected (36% in low, 26% in medium and 90% in high human Mf-density). Survival analysis showed that the parasite load in mosquitoes and the human Mf-density for a given parasite load are independent risk factors of vector survival. Overall, the hazard of dying was found to be 11–15 times higher among mosquitoes fed on microfilaraemic volunteers than those fed on amicrofilaraemics. The hazard doubles for every increase of about 60–70 parasites in the vector. As a consequence of the parasite-induced reduction in vector survival, the transmission success of the parasite is reduced. The implication of the results on control/elimination of lymphatic filariasis using mass-drug administration is discussed.

The fact that the Schistosoma mansoni egg has two ATP diphosphohydrolase (EC 3.6.1.5) isoforms with different net charges and an identical molecular weight of 63000, identified by non-denaturing polyacrylamide gel electrophoresis and immunological cross-reactivity with potato apyrase antibodies, is shown. In soluble egg antigen (SEA), only the isoform with the lower net negative charge was detected and seemed to be the predominant species in this preparation. By confocal fluorescence microscopy, using anti-potato apyrase antibodies, the S. mansoni egg ATP diphosphohydrolase was detected on the external surface of miracidium and in von Lichtenberg's envelope. Intense fluorescence was also seen in the outer side of the egg-shell, entrapped by the surface microspines, suggesting that a soluble isoform is secreted. ATP diphosphohydrolase antigenicity was tested using the vegetable protein as antigen. The purified potato apyrase was recognized in Western blots by antibodies present in sera from experimentally S. mansoni-infected mice. In addition, high levels of IgG anti-ATP diphosphohydrolase antibodies were detected by ELISA in the same sera. This work represents the first demonstration of antigenic properties of S. mansoni ATP diphosphohydrolase and immunological cross-reactivity between potato apyrase and sera from infected individuals.

Knowledge about how parasites choose their hosts is scarce and incomplete. Recent work has primarily focused on host health (i.e. immunocompetence) whereas ecological factors have been largely neglected. Here we investigate whether the immunocompetence, the nutritional condition or body size of nestling European bee-eaters Merops apiaster are used as parameters for habitat choice of the haematophagous fly Carnus hemapterus. We found that (i) flies consistently and non-randomly preferred larger nestlings, even after controlling for differences in habitat availability (host surface), (ii) in the presence of similar-sized hosts, parasites' choice for an individual was less likely than if hosts differed in size, (iii) the more the hosts differed in size, the more the parasites aggregated on the larger nestling and (iv) parasites changed their preference according to size criteria regardless of the identity of the larger host. Neither immunocompetence nor host body condition could account for parasites' preference. Our results do not support the prediction of the Tasty Chick Hypothesis, namely that the poor immunocompetence ability of junior chicks makes them more attractive to parasites. We conclude that basic ecological factors (e.g. body size) can be essential for parasites when choosing a host.

Most studies on the effects of tanniferous plants on nematodes have examined forages but have neglected the woody plants. Therefore, in vitro effects of extracts from 3 woody plants (Rubus fructicosus, Quercus robur, Corylus avellana) have been tested on trichostrongyles and compared to sainfoin, a legume forage. Because some in vivo results indicated that the effects of tannins differed depending on the parasitic species and/or stages, the effects were measured on 3rd-stage larvae (L3) and adult worms of Teladorsagia circumcincta, Haemonchus contortus and Trichostrongylus colubriformis. The effects of plant extracts varied according to the plant sources, the parasite species and stages. For the woody plants, significant inhibitory effects were obtained on both stages of abomasal species. Results for T. colubriformis were more variable. Effects of sainfoin extracts were significant on T. colubriformis and H. contortus L3, and on abomasal adult worms. In order to assess the implications of tannins, polyethylene glycol (PEG), an inhibitor of tannins, was added to hazel tree, oak and sainfoin extracts. Without PEG, significant inhibitory effects on L3 and adult worms were confirmed. After addition of PEG, the larval migration and motility of adult worms were restored in most cases. These results confirm variations in effects depending on factors related to plants or parasites and suggest that tannins are partly responsible for the effects.

Two superoxide dismutases (SODI and SODII) have been purified by differential centrifugation, fractionation with ammonium sulphate followed by chromatographic separation (ionic exchange and affinity), from a plant trypanosomatid isolated from Euphorbia characias, and then characterized for several biochemical properties. Both enzymes were insensitive to cyanide but sensitive to hydrogen peroxide, properties characteristic of iron-containing superoxide dismutase. SODI had a molecular mass of approximately 66 kDa, whereas the molecular mass of SODII was approximately 22 kDa, both enzymes showing single bands. The isoelectric points of SODI and SODII were 6·8 and 3·6, respectively. The enzymatic stability persisted at least for 6 months when the sample was lyophilized and preserved at −80 °C. Digitonin titration and subcellular fractionation showed that both enzymes were in the cytoplasmic fraction, although part of SODII isoenzyme was also associated with glycosomes. We assayed these activities (SOD) in 18 trypanosomatid isolates on isoelectric focusing gels, and have demonstrated that the SOD is a biochemical marker sufficient to identify a trypanosomatid isolated from a plant as belonging to the genus Phytomonas and to distinguish between a true Phytomonas and other trypanosomatids that are capable of causing transient infections in plants.

In the production of the infective cercariae of trematodes, the terminal investment hypothesis of life-history theory predicts that the rate of host exploitation and cercarial production should increase during the period of cercarial shedding since the reproductive value of the parasite decreases during this period. In contrast, a bet hedging hypothesis that focuses on the success of transmission when host contact rate is variable predicts that cercarial production should decrease in an attempt to keep the host alive for longer and thus would increase the probability of successful transmission. We examined these two hypotheses under laboratory conditions and recorded the production of Diplostomum spathaceum cercariae from naturally infected snail hosts, Lymnaea stagnalis. The average number of cercariae produced per day decreased as the snail host approached death counter to the terminal investment hypothesis. The finding supports the prediction of the bet hedging hypothesis and implies that the pattern of cercarial production may be explained by reduced virulence of the parasite within the snails to ensure extended total production time of cercariae. Nevertheless, survival of infected snails was still lower than uninfected snails suggesting that ultimately the infection still increased snail mortality rate. Cercarial production varied between days but was not cyclic, probably because of the physiology of the sporocysts within snails. Fewer cercariae were released at night, which may increase transmission efficiency to diurnally-active fish hosts. The mechanisms associated with daily cercarial production are discussed.

The fox tapeworm Echinococcus multilocularis is typically perpetuated in a cycle with red foxes as definitive hosts and various rodent species as intermediate hosts. In this study, foxes were baited with a highly efficient drug against cestodes (praziquantel) in 5 blocks of 1 km2. Voles, Arvicola terrestris, the most abundant intermediate host species, were trapped in the 5 baited blocks and in 5 non-baited control blocks. Baiting the foxes reduced the prevalence of E. multilocularis in fox faecal samples in the baited blocks, but voles trapped in the two blocks did not differ in their infection rates. However, voles from the baited blocks had significantly smaller spleen masses and were more likely to be infested with mites than those from the control blocks, possibly reflecting different immunological activities. Our study suggests that the environmental contamination with E. multilocularis eggs, and perhaps those of other tapeworms, influences the immune system of the intermediate host species A. terrestris in the wild.

Parasite community ecology has recently focused on understanding the forces structuring these communities. There are few surveys, however, designed to study the spatial repeatability and predictability of parasite communities at the local scale in one host. The purpose of our study was to address the relationship between infracommunity and component community richness, and to describe spatial variations on the local scale, of helminth parasite communities in an avian host, the red-legged partridge (Alectoris rufa). We sampled 235 wild partridges from 8 separate localities, with different partridge population densities, in the Ciudad Real and Toledo provinces of central Spain, and we determined their overall and intestinal helminth species. We found that habitat variables (mean temperature and land use) were not significantly associated with any component community. The partridge population abundance index was directly correlated with the prevalence and mean intensity of infection but not with component community species richness. There was a curvilinear relationship between infracommunity and component community species richness, as well as negative interspecific associations, for the helminth species assemblage parasitizing the intestine. A nestedness/anti-nestedness pattern, considered as part of a continuum, was associated with prevalence, mean intensity and partridge population abundance index, but not with component community richness. Increases in the partridge population abundance index and the prevalence and mean intensity of infection were associated with increases in helminth community nestedness. Although negative interactions between helminth species could not be ruled out as forces structuring helminth communities, our results suggest that parasite community structure in the red-legged partridge was primarily determined by the extrinsic influence of parasite habitat heterogeneity and its amplification of the differing probabilities of colonization of parasite species.

A copro-antigen capture ELISA for the detection of Teladorsagia circumcincta infection in sheep was developed and evaluated. Experiments with faeces from worm-free sheep, that had been spiked with known concentrations of excretory–secretory (E–S) antigen indicated that a positive signal was generated with 180 ng of E–S/ml. A nested design, based on 8 infected and 8 worm-free sheep, was employed to assess the stages during sample preparation contributing to variation in signal from the assay. This showed that 87% of the variance in the optical density readings (ODs) was directly explained by infection status. Variation between individual sheep within infection groups, and between samples at various stages in the assay, collectively accounted for the remaining variance. Initial evaluation of specificity using faeces from animals carrying a range of monospecific infections indicated cross-reactivity with Haemonchus contortus and Nematodirus spathiger. However, by treating the supernatant from faeces for 20 min at 100 °C, the cross-reactive signal was eliminated whilst the specific signal was largely preserved. Heat treatment of faeces from 12 non-infected sheep, 12 sheep with T. circumcincta and 6 with H. contortus resulted in sensitivity being increased from 66·7 to 85·7%, and specificity from 62·5 to 87·5%. OD values showed a significant positive relationship with adult worm burdens, although at low infection intensities there was some overlap between infected and worm-free animals. We discuss the application of CC-ELISAs in facilitating selective chemotherapy of sheep, as a means of avoiding the development of anthelmintic resistance in pastoral regions where sheep are farmed on a large scale.