Although the folate metabolic pathway in malaria parasites is a major chemotherapeutic target, resistance to currently available antifolate drugs is an increasing problem. This pathway, however, includes a number of enzymes that, to date, have not been characterized despite their potential for clinical exploitation. As a step towards evaluation of additional targets in this pathway, we report the isolation and characterization of 3 new genes that encode homologues of GTP cyclohydrolase I (GTP-CH), dihydrofolate synthase/folylpolyglutamate synthase (DHFS/FPGS) and serine hydroxymethyltransferase (SHMT). The genes encoding GTP-CH and SHMT are unambiguously assigned to chromosome 12, while that for DHFS/FPGS is tentatively assigned to chromosome 13. All 3 genes are expressed in blood-stage parasites, yielding transcripts of which only ca 60–70% is accounted for by coding sequence. All 3 of the proteins predicted to be encoded by these genes display sequence differences compared to the human host homologues that may be of functional significance. These data bring the complement of cloned genes that encode activities in the pathway to seven, leaving only the gene encoding dihydroneopterin aldolase (DHNA) to be identified in the route from GTP to folate synthesis and folate turnover in the thymidylate cycle.

Plasmodium berghei ookinete formation in vitro and within the midgut of susceptible Anopheles atroparvus were compared. No significant morphological differences were seen, except that in vitro development was more synchronized and less degenerating forms occurred. In vitro ookinete yields were 4–31 times higher and less variable than those in vivo. Mosquitoes of a susceptible and of a refractory line of A. atroparvus were simultaneously fed on the same host or via a membrane with the same suspension of in vitro-formed mature ookinetes. Up to 100% of mosquitoes of the susceptible line produced oocysts, mostly in high numbers, whereas infection rates and numbers of oocysts produced in mosquitoes of the refractory line were lower and much more so after host feeding than after membrane feeding of mature ookinetes, indicating that refractoriness does not depend on a single process of inhibition.

Two kinds of community structure referred to, nestedness and bimodal distribution, have been observed or were searched for in parasite communities. We investigate here the relation between these two kinds of organisation, using marine fishes as a model, in order to show that parasite population dynamics may parsimoniously explain the patterns of ectoparasite species distribution and abundance. Thirty six assemblages of metazoan ectoparasites on the gills and heads of marine fish showed the following patterns: a positive relationship between abundance and the variance of abundance; a positive relationship between abundance and prevalence of infection; a bimodal pattern of the frequency distribution of prevalence of infection; nestedness as indicated by Atmar and Patterson's thermodynamic measure (a mean of 7.9°C); a unimodal distribution of prevalence in parasite assemblages with a temperature lower than the mean, and a bimodal distribution in assemblages with a temperature higher than the mean. We conclude that patterns are the result of characteristics of the parasite species themselves and that interspecific competition is not necessary to explain them. We emphasize that a holistic approach, taking all evidence jointly into account, is necessary to explain patterns of community structure. Ectoparasite assemblages of marine fish are among the animal groups that have been most thoroughly examined using many different methods, and all evidence supports the view that these animals live under non-equilibrium conditions, in largely non-saturated niche space in which interspecific competition occurs but is of little evolutionary importance.

In 1928, a collection of marine fish trematodes was made at the United States Bureau of Fisheries Station at Beaufort, North Carolina; thirty-six of fifty-one species of fishes examined contained trematodes; only one or two specimens of some species were examined. Only Monogenea were collected from Elasmo branchs. The following report includes the digenetic forms identified. Type specimens of all new species are deposited in the United States National Museum.

Toxoplasma gondii (T. gondii) infects one-third of the world population, but its association with cognitive functions in school-aged children is unclear. We examined the relationship between Toxoplasma seropositivity and neuropsychological tests scores (including math, reading, visuospatial reasoning and verbal memory) in 1755 school-aged children 12–16 years old who participated to the Third National Health and Nutrition Examination Survey, using multiple linear regressions adjusted for covariates. Toxoplasma seroprevalence was 7·7% and seropositivity to the parasite was associated with lower reading skills (regression coefficient [β] = −5·86, 95% confidence interval [CI]: −11·11, −0·61, P = 0·029) and memory capacities (β = −0·86, 95% CI: −1·58, −0·15, P = 0·017). The interaction between T. gondii seropositivity and vitamin E significantly correlated with memory scores. In subgroup analysis, Toxoplasma-associated memory impairment was worse in children with lower serum vitamin E concentrations (β = −1·61, 95% CI: −2·44, −0·77, P < 0·001) than in those with higher values (β = −0·12, 95% CI: −1·23, 0·99, P = 0·83). In conclusion, Toxoplasma seropositivity may be associated with reading and memory impairments in school-aged children. Serum vitamin E seems to modify the relationship between the parasitic infection and memory deficiency.

A study has been made of the damage incurred by normal and Plasmodium falciparum-infected human erythrocytes following exposure to a variety of oxidant-generating systems. Hydrogen peroxide, produced by the glucose–glucose oxidase system, increased methaemoglobin formation within normal erythrocytes while normal levels of oxyhaemoglobin were maintained. Exposure to products of the xanthine–xanthine oxidase interaction did not have the same effect. Malondialdehyde measurements indicated that the host cell membranes of parasitized cells had undergone lipid peroxidation even before exposure to the oxidant-generating systems. Lipid peroxidation of normal and parasitized cell membranes was increased upon exposure to reagent-grade hydrogen peroxide and alloxan: this increase was not observed following exposure to the two enzyme–substrate systems that generated reactive oxygen intermediates. In addition, the effects of parasitism on intracellular levels of catalase and superoxide dismutase were assessed. Normal and parasitized erythrocytes were found to possess similar levels of these enzymes, which protect against oxidant-induced damage. It was therefore concluded that the increased susceptibility of infected cells to oxidant damage was probably not related to any decrease in the function of these enzymes.

The mathematical model of the in-host dynamics for malaria parasites of Anderson, R. M., May, R. M. & Gupta, S. (1989), Parasitology99 (Suppl.) S59–S79, and subsequently used by other authors, contains an error. This leads to very substantial over-estimates in parasite growth rates. A corrected form of the model is presented in this paper.

The forms under consideration resemble Rickettsia prowazeki—the supposed cause of typhus fever—which occurs in lice that have fed on typhus fever patients.

Oocysts of the Weybridge and Houghton strains of Eimeria maxima and a fresh field isolate were similar and measured on average 30·9 × 22·4 μm. The Weybridge strain and the field isolate produced similar pathogenic effects in 6-week-old chickens, high doses causing 50–80% mortality and severe weight loss. The Houghton strain was slightly less pathogenic and few birds died but more oocysts were produced. With each strain, a single dose gave complete immunity to a light challenge with the homologous strain. Two or 3 immunizing doses gave complete immunity to a heavy homologous challenge but were not sufficient to protect against heterologous challenge.

Although parasite communities have been studied extensively in recent years, spatial and temporal variation in factors affecting the communities has received less attention. This paper examined the similarity of parasite assemblages of perch (Perca fluviatilis) in 18 locations within a single lake in relation to geographical distance and temporal dynamics in the host and parasite populations. We expected that in the present study-scale where distinct but potentially interacting host subpopulations could occur, similarity of the assemblages could be affected by seasonal dynamics in host movements particularly during the spawning period. Parasite species showed differences in infection levels between the sampling locations and similarity of the assemblages of autogenic parasite species in winter, measured inversely as difference in parasite numbers, was negatively affected by geographical distance between the locations. However, no such relationship was observed in the allogenic species Ichthyocotylurus variegata. Furthermore, no relationship was found either in autogenic parasites when the locations were re-sampled in summer, after the spawning period of perch. We concluded that the effect of geographical distance on the similarity of parasite assemblages is a dynamic process, which is affected by seasonal dynamics in host and parasite populations.

The distribution of the acanthocephalan Pomphorhynchus laevis along the alimentary tract of several species of freshwater fish was studied in both natural and experimental infections. The parasite exhibits a clear preference for a particular region of the alimentary canal, which differs from host species to host species, but it is capable of surviving in all regions of the intestine. In some host species, but not in all, its growth rate may be reduced in regions outside of the preferred site. The parasite remains in the same site throughout the period of infection, emigrations occurring only preparatory to complete loss of the parasite from the host. The presence of cestodes in the region of the preferred site has no effect upon the distribution of the parasite. At high levels of infection the range of the parasite's distribution is extended. The feeding of larval parasites to fish by stomach tube also leads to an extension of range, whereas when fish are allowed to feed on cystacanths removed from their intermediate host the parasite establishes in a more anterior position than usual and in a site that it does not occupy to any extent in natural infections. It is concluded that the distribution of P. laevis in the alimentary canal offish is determined primarily by the process of liberation, activation and establishment of the parasite, and that it normally attaches in the first available space and remains there. Unsuitable physico-chemical or feeding conditions affect only its growth, not the site that it occupies. It is suggested that P. laevis may be atypical in this respect.

Successful metazoan parasitism, among many other factors, requires a supply of nutrients and the removal of waste products. There is a prerequisite for a parasite-defined vasculature. The angiogenic mechanism(s) involved presumably depend on the characteristics of the tissue- and vascular system-dwelling, parasitic helminths. Simplistically, 2 possibilities or a combination of both have been considered in this review. The multifactorial induction of parasitic helminth-associated neovascularization could arise through, either a host-, a parasite- or a host-/parasite-dependent, angiogenic switch. Most studies appear to support the first and third hypotheses, but evidence exists for the intrahepatic cestode Echinococcus multilocularis, the free-living nematode Caenorhabditis elegans and the intravascular trematode Schistosoma mansoni for the second inference. In contrast, the nematode anti-coagulant protein NAPc2 from adult Ancylostoma caninum is also an anti-angiogenic factor.

The multifaceted interactions occurring between gastrointestinal (GI) parasitic helminths and the host gut microbiota are emerging as a key area of study within the broader research domain of host-pathogen relationships. Over the past few years, a wealth of investigations has demonstrated that GI helminths interact with the host gut flora, and that such interactions result in modifications of the host immune and metabolic statuses. Nevertheless, whilst selected changes in gut microbial composition are consistently observed in response to GI helminth infections across several host-parasite systems, research in this area to date is largely characterised by inconsistent findings. These discrepancies are particularly evident when data from studies of GI helminth-microbiota interactions conducted in humans from parasite-endemic regions are compared. In this review, we provide an overview of the main sources of variance that affect investigations on helminth-gut microbiota interactions in humans, and propose a series of methodological approaches that, whilst accounting for the inevitable constraints of fieldwork, are aimed at minimising confounding factors and draw biologically meaningful interpretations from highly variable datasets.

Plasmodium falciparum, P. knowlesi and P. chabaudi showed a significant activity of methylenetetrahydrofolate reductase (MTHFR). The presence of this enzyme completes the methionine synthesis cycle, in which the one-carbon fragment from serine side-chain can be transferred to methionine. However, while metabolic labelling of methionine from l-3 [14C]serine could not be demonstrated in P. falciparum, the significance of MTHFR was implicated by a novel pathway for salvage of exogenous 5-methyltetrahydrofolate from the host cell. The methyl group of the cofactor was incorporated into methionine, and the folate cofactor was found in the same pool as that derived from de novo synthesis with paminobenzoic acid as the precursor, shown previously as polyglutamylated 5-methyltetrahydrofolate. It is proposed from these results that the function of MTHFR and the methionine synthesis cycle is not the supply of methionine, but the generation of active folate cofactors from more stable precursors salvaged by the parasites

Oxidative stress has been implicated as an important pathogenic factor in the pathophysiology of various life-threatening diseases such as cancer, cardiovascular diseases and diabetes. It occurs when the production of free radicals (generated during aerobic metabolism, inflammation, and infections) overcome the antioxidant defences in the body. Although previous studies have implied that oxidative stress is present in serum of patients with parasitic infection there have been no studies confirming oxidative stress levels in the Malaysian population infected with intestinal parasites. Three biochemical assays namely hydrogen peroxide (H2O2), lipid peroxidation (LP) and advanced oxidative protein product (AOPP) assays were carried out to measure oxidative stress levels in the urine of human subjects whose stools were infected with parasites such as Blastocystis hominis, Ascaris, Trichuris, hookworm and microsporidia. The levels of H2O2, AOPP and LP were significantly higher (P<0·001, P<0·05 and P<0·05 respectively) in the parasite-infected subjects (n=75) compared to the controls (n=95). In conclusion, the study provides evidence that oxidative stress is elevated in humans infected by intestinal parasites. This study may influence future researchers to consider free radical-related pathways to be a target in the interventions of new drugs against parasitic infection and related diseases.

Rats harbouring a 35-day-old primary infection of Moniliformis dubius were inoculated with constant doses of Nippostrongylus brasiliensis and 10 days later, after post mortem examination, rats with concurrent infections harboured significantly fewer Nippostrongylus than rats with single infections. Similar infections of Moniliformis were carried out, but with post mortem taking place on days 8,9, 12 and 14 of the Nippostrongylus infections. On days 8 and 9 of infection, rats with concurrent infections did not harbour significantly fewer Nippostrongylus compared with single infections. Both single and concurrent infections of 12-and 14-day-old Nippostrongylus were found to harbour lower numbers of worms. In the single infection this corresponds to the timing of the typical immune expulsion of a primary single infection which takes place on approximately day 12 of infection. The Moniliformis population was not significantly affected, in terms of numbers, dry weight and length, although each parasite population did show a slight shift in site in the presence of the other. A significant reduction in egg production by Nippostrongylus was detected throughout concurrent infection. The possible role of non-reciprocal cross-immunity is discussed as an explanation for the apparent early expulsion of the Nippostrongylus population in the presence of Moniliformis.

Trypanosomes were isolated before and after the formation of infected detectable antibody from various brain sites and the blood of Microtus montanus. All isolates were serotyped by the agglutination reaction, and the isolates obtained prior to antibody formation were serologically identical to the original inoculum. Later isolates obtained from separate sites of an infected animal were serologically different from the original inoculum and also from each other. It was therefore concluded that in a single chronically infected animal there are numerous different antigenic populations of trypanosomes each occupying separate brain sites. A hypothesis to account for this antigenic diversity is given.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been recently described as an innovative and effective tool for identifying arthropods and mosquito blood meal sources. To test this approach in the context of an entomological survey in the field, mosquitoes were collected from five ecologically distinct areas of Mali. We successfully analysed the blood meals from 651 mosquito abdomens crushed on Whatman filter paper (WFPs) in the field using MALDI-TOF MS. The legs of 826 mosquitoes were then submitted for MALDI-TOF MS analysis in order to identify the different mosquito species. Eight mosquito species were identified, including Anopheles gambiae Giles, Anopheles coluzzii, Anopheles arabiensis, Culex quinquefasciatus, Culex neavei, Culex perexiguus, Aedes aegypti and Aedes fowleri in Mali. The field mosquitoes for which MALDI-TOF MS did not provide successful identification were not previously available in our database. These specimens were subsequently molecularly identified. The WFP blood meal sources found in this study were matched against human blood (n = 619), chicken blood (n = 9), cow blood (n = 9), donkey blood (n = 6), dog blood (n = 5) and sheep blood (n = 3). This study reinforces the fact that MALDI-TOF MS is a promising tool for entomological surveys.

The tegumental membrane complex of Schistosoma mansoni is the site of interaction between the parasite and the host. The tegument is involved in uptake of many nutrients, but also plays a crucial role in the evasion of the actions of the host immune system. Essential for the success of this evasion is maintaining the integrity of the tegumental membranes. The rate of turnover of phospholipids was investigated by pulse-labelling worms cultured in vitro, followed by additional incubation in the presence of unlabelled substrates. Tegumental membranes were isolated, characterized using antibodies against specific tegumental proteins, and analysed. It was demonstrated that the most prominent fatty acid found in tegumental phospholipids, palmitate, incorporated rapidly into the phospholipid fraction during a 30 min pulse labelling. In a subsequent 20 h chase with unlabelled substrates, the incorporated radioactivity was lost again from the tegumental membrane complex. This high turnover of palmitate was found to be limited to phosphatidylcholine (PC) only. The turnover was due to deacylation/reacylation, and not to the sloughing of membranes as is the case in schistosomula. It is speculated that this rapid turnover of PC in the tegument of adult schistosomes plays a new and important role in the immune evasion by the parasite.

The sanitary control of threatened wild animals is of pivotal interest for their conservation. This task, however, is highly complex in wildlife/livestock systems. In this paper we report findings from a 2-year cross-sectional study of the epidemiology and attempted control of a Sarcoptes mite infestation in the threatened cheetah population in Masai Mara (Kenya), and discuss its interaction with sympatric wild (lion, wildebeest and Thomson's gazelle) and domestic (dog, cattle and sheep) animals. Sarcoptes scabiei was isolated from cheetahs, Thomson's gazelles, wildebeests, lions, cattle, goats and dogs; Psoroptes ovis, on the other hand, was only isolated from sheep. The prevalence study revealed 12·77% infection rates in cheetahs, 4·7% in dogs, 0·8% in Thomson's gazelles, 0·8% in sheep, 0·09% in cattle, and 0·09% in goats, while it opportunistically affected lions and wildebeest. Our study revealed that prevalence of Sarcoptes mite in cheetah population was not associated with the studied geographical blocks, animal sex or the presence of affected domestic animals. Cheetah infection with S. scabiei was associated with the climatic conditions (dry more than wet season) and the balancing between the total number of Thomson's gazelles and the prevalence of infected individuals. Apparently the high prevalence of mangy gazelles has a negative effect on cheetah; this negative effect was reduced when the number of healthy gazelles was increased. Treatment with injectable ivermectin of the clinically affected wild and domestic animals during the first year of this study was associated with much lower incidence of sarcoptic mange during the second year.