The life-history of I. pacificus when fed on guinea-pigs under laboratory conditions is described. Feeding of the female proceeds for 10–11 days. Between 120 and 191 mg of concentrated food is found in the female's gut on detaching from this host, and this is directly related to the unfed body weight of the tick.

The egg-laying pattern, in general, shows an initial peak, after which the number of eggs tails off, the whole process lasting approximately 33–40 days. The number of eggs laid by females varies between 790 and 1300. The preoviposition period is about 11–16 days.

Larvae hatch in about 53–55 days, and their feeding time ranges from 4 to 9 days, although in the present experiments larvae emerging from early laid eggs took about 10 days to complete engorgements.

Moulting of larvae to nymphs at 90% R.H. took 37–38 days, and nymphs fed for 7–11 days, with most becoming replete on the ninth.

Very few females emerged from these nymphs, and those that did emerged in just over 30 days. The reasons for this are not clear. No diapause appeared to be necessary to complete the life-cycle, and with due allowance for hardening of the mouthparts the life-history of one generation was about 7 months. Females died within 3 or 4 months if hosts were not available.

From the literature and from hitherto unpublished records some 55 vertebrates have been implicated as hosts to I. pacificus; these hosts include a wide range of mammals, six species of birds and possibly nine species of lizards.

The species has been listed from British Columbia and from five western states of U.S.A. The need for more intensive ecological work on this species is emphasized.

We are indebted to Glen M. Kohls, J. D. Gregson and D. E. Johnstone for permission to use unpublished records from their respective institutions. One of us (D.R.A) is also indebted to the Wellcome Trustees for financial assistance to visit Canada during the preliminary stages of the work.

Cyclospora cayetanensis is a coccidian parasite associated with diarrheal illness. In the USA, foodborne outbreaks of cyclosporiasis have been documented almost every year since the mid-1990s. The typical approach used to identify this parasite in human stools is an examination of acid-fast-stained smears under bright-field microscopy. UV fluorescence microscopy of wet mounts is more sensitive and specific than acid-fast staining but requires a fluorescence microscope with a special filter not commonly available in diagnostic laboratories. In this study, we evaluated a new DNA extraction method based on the Universal Nucleic Acid Extraction (UNEX) buffer and compared the performances of four published real-time polymerase chain reaction (PCR) assays for the specific detection of C. cayetanensis in stool. The UNEX-based method had an improved capability to recover DNA from oocysts compared with the FastDNA stool extraction method. The best-performing real-time PCR assay was a C. cayetanensis-specific TaqMan PCR that targets the 18S ribosomal RNA gene. This new testing algorithm should be useful for detection of C. cayetanensis in human stool samples.

The effect of sainfoin (Onobrychis viciifolia) hay consumption on the pathophysiology and local cellular responses of growing lambs during infection with Trichostrongylus colubriformis was investigated. Thirty-two lambs, 16 weeks of age, were allocated to 1 of 4 treatment groups (n=8) that were offered either grass (G) or sainfoin (S) hay while concurrently either infected (+), or not (−) with 12 000 L3 T. colubriformis larvae per week for 6 weeks. Liveweight gains were affected by diet (P=0·002) and reduced by infection (P<0·005). Faecal egg count was reduced in S+ compared to G+from days 35 to 42 (P=0·001); however, total egg output, worm burdens at day 42 and worm fecundity were similar between diets (P>0·05). Feeding sainfoin appeared to enhance immune cell development with tissue eosinophils, mast cells and pan T cells present in greater concentrations in S+ than in G+ animals. However, further studies are required to determine if the enhanced immune cell development is a consequence of a greater nutrient supply or a direct influence of sainfoin metabolites on local inflammatory responses to the gastrointestinal nematode T. colubriformis.

The usage of alternative synonymous codons in the completely sequenced, extremely A+T-rich parasite Plasmodium falciparum was studied. Confirming previous studies obtained with less than 3% of the total genes recently described, we found that A- and U-ending triplets predominate but translational selection increases the frequency of a subset of codons in highly expressed genes. However, some new results come from the analysis of the complete sequence. First, there is more variation in GC3 than previously described; second, the effect of natural selection acting at the level of translation has been analysed with real expression data at 4 different stages and third, we found that highly expressed proteins increment the frequency of energetically less expensive amino acids. The implications of these results are discussed.

In order to estimate the value of population genetics for both the taxonomy of trypanosomes belonging to the species Trypanosoma brucei and a better understanding of Human African Trypanosomiasis (HAT), we undertook a cellulose acetate electrophoresis isoenzyme study involving 55 stocks isolated from man and animals in Congo, Zaire and Cameroun. Out of the 24 loci surveyed, 15 exhibited variability, which made it possible to delimit 23 zymodemes, divided into 2 groups. The first group equated to the classical subspecies Trypanosoma brucei gambiense, while the second corresponded to the classical subspecies Trypanosoma brucei brucei. These results broadly agree with the current taxonomy, and are corroborated by RFLP analysis of kDNA. Statistical analysis indicates a basically clonal reproduction system of the trypanosomes in the area studied; the zymodemes are equivalent to natural clones (or a family of closely related clones), stable in space and time. Epidemiological hypotheses are proposed according to the geographic distribution of the clones in this area.

In the present study we detected Schellackia haemoparasites infecting the blood cells of Lacerta schreiberi and Podarcis hispanica, two species of lacertid lizards from central Spain. The parasite morphometry, the presence of a refractile body, the type of infected blood cells, the kind of host species, and the lack of oocysts in the fecal samples clearly indicated these blood parasites belong to the genus Schellackia. Until now, the species of this genus have never been genetically characterized and its taxonomic position under the Lankesterellidae family is based on the lack of the exogenous oocyst stage. However, the phylogenetic analysis performed on the basis of the 18S rRNA gene sequence revealed that species of the genus Schellackia are clustered with Eimeria species isolated from a snake and an amphibian species but not with Lankesterella species. The phylogenetic analysis rejects that both genera share a recent common ancestor. Based on these results we suggest a revision of the taxonomic status of the family Lankesterellidae.

Vaccination with whole male worm extract (AMA), stichoseome extract (SA) and a short-term inculbation fluid (EXA) of adult Trichuris muris induced a high degree of protective immunity in mice as assessed by reduction in larval worm burden.

Immunodiffusion of AMA against rabbit anti-AMA serum revealed five precipitin lines, one of which was common to both EXA and SA with which only single lines were obtained.

Physico-chemical tests suggested that the antigen is a protein and that carbohydrate, lipid and DNA do not contribute to its antigenicity. Partial fractionation was obtained with ammonium sulphate. All preparations with immunogenic activity showed the common line of EXA on immunodiffusion.

It is concluded that one of the protective immunogens is a protein which can be associated with the precipitin line and originates in the stichosome.

Lambs were infected at daily intervals from 3 weeks of age with increasing doses of infective larvae of Trichostrongylus colubriformis, according to an exponential infection schedule designed to simulate the pattern of infection experienced by grazing lambs during the spring and early summer in Britain. The faecal egg counts and the worm burdens in the lambs followed a similar exponential trend for 12 weeks after initial infection.

The T. colubriformis burdens in these lambs appeared to be cumulative during the first 12 weeks, after which the animals developed a resistance to further reinfection, which was very strong by 16 weeks after initial infection. However, even lambs which were refractory to new infection continued to harbour large numbers of adult worms, which caused clinical disease in most of the lambs.

There was no evidence to suggest that either a turnover of the worm burden, inhibition of larval development or the sudden loss of established parasites played any major role in the regulation of the burdens of T. colubriformis in these young lambs.

The removal of the established burden 16 weeks after initial infection in one lamb appeared to result in a partial loss of resistance to a challenge infection given 10 days later.

1. The spores of Eimeria (not the oocysts) are the real infective agents and, as in other Sporozoa, they readily set free their sporozoites in the duodenum or in vitro under suitable conditions.

2. The protective oocyst has double walls: the ectocyst is thick and impervious to fluids but easily fractures by mechanical means, such as drying. Even though cracked, it may continue to protect the thin endocyst and spores until they reach the specially muscular regions of the alimentary canal. Free spores are probably also sometimes ingested.

3. The ectocyst is a continuous envelope without a persistent micropyle. It resembles keratin in many ways.

Nine clones were derived from a drug-resistant Trypanosoma congolense stock (IL 2856) and characterized in mice for their sensitivity to isometamidium chloride and diminazene aceturate. All clones were derived from the stock without drug selection and expressed high levels of resistance to isometamidium chloride (50% curative dose [CD50] values ranging from 1·5 to 5·1 mg/kg) and intermediate to high levels of resistance to diminazene aceturate (CD50 values ranging from 5·1 to 21·0 mg/kg). By contrast, the isometamidium chloride and diminazene aceturate CD50 values for a drug-sensitive clone, T. congolense IL 1180, were 0·018 mg/kg and 2·3 mg/kg, respectively. For both drugs, there appeared to be significantly different levels in expression of drug resistance amongst the 9 clones derived from IL 2856. Isoenzyme analysis of 7 enzymes showed that all 9 clones expressed the same electrophoretic variants. Thus, all 9 clones were identical for these phenotypic markers. The clone which expressed the highest level of resistance to isometamidium in mice (IL 3270) was transmitted to Boran cattle via the bite of infected Glossina morsitans centralis. IL 3270 produced an infection rate in tsetse of 5·0%. The resulting infections in cattle were shown to be resistant to intramuscular treatment with 2·0 mg/kg isometamidium chloride and 14·0 mg/kg diminazene aceturate. This contrasts with doses of 0·25 mg/kg isometamidium chloride or 3·5 mg/kg diminazene aceturate which are deemed sufficient to cure fully sensitive infections. Finally, 9 clones (subclones) were derived from IL 3270 and characterized in mice for their sensitivity to isometamidium chloride. Seven of the subclones expressed a significantly lower level of resistance to isometamidium than the parental clone and amongst the subclones there was significant variation in resistance. Thus, expression of a high level of resistance to isometamidium appears to be unstable in the rodent host and at least a component of the genetic determinant(s) for this drug-resistant phenotype is (are) likely to be unstable.

Several approaches were adopted for the disruption and removal of the tegumental surface from protoscoleces of the horse strain of the hydatid organism, Echinococcus granulosus. The effectiveness of each method and the purity of subsequent microthrix-enriched fractions obtained by differential centrifugation were evaluated by electron microscopy, by the amount of protein released and by the degree of enrichment of surface plasma membrane marker enzymes. Incubation in saponin for 10 min produced the purest microtriche preparation, but in low yield; freeze/thawing, incubation in Triton X-100 for 10 mm or in saponin for 20 min produced fractions containing significant amounts of relatively pure microtriches, but mild homogenization was a poor method for surface disruption and subsequent isolation of microtriches. Phosphodiesterase, adenosine triphosphatase (total and ouabain-inhibited), leucine aminopeptidase and glutamyltransferase were active in the protoscoleces but none were enriched in any of the microthrix fractions. In contrast, alkaline phosphatase, acid phosphatase, 5′ nucleotidase and maltase were enriched significantly in all of the isolated microtriche preparations, which suggests that these enzymes are predominantly surface membrane bound. The protein profiles of the microthrix-enriched fractions, following SDS—PAGE, were basically similar, although there were some qualitative and quantitative differences in the proteins released by each isolation procedure. Three major PAS-staining components were present in all the preparations and these probably originated from the glycocalyx. One of these PAS-positive components, with an approximate molecular weight of 110 kDa, may be a glycoprotein specific to the horse strain of E. granulosus.

Acetylcholine is the major excitatory neurotransmitter controlling motor activities in nematodes, and the enzyme which hydrolyses and inactivates acetylcholine, acetylcholinesterase, is thus essential for regulation of cholinergic transmission. Different forms of acetylcholinesterase are encoded by multiple genes in nematodes, and analysis of the pattern of expression of these genes in Caenorhabditis elegans suggests that they perform non-redundant functions. In addition, many parasitic species which colonise host mucosal surfaces secrete hydrophilic variants of acetylcholinesterase, although the function of these enzymes is still unclear. Acetylcholinesterases have a history as targets for therapeutic agents against helminth parasites, but anti-cholinesterases have been used much more extensively as pesticides, for example to control crop damage and ectoparasitic infestation of livestock. The toxicity associated with these compounds (generally organophosphates and carbamates) has led to legislation to withdraw them from the market or restrict their use in many countries. Nevertheless, acetylcholinesterases provide a good example of a neuromuscular target enzyme in helminth parasites, and it may yet be possible to develop more selective inhibitors. In this article, we describe what is known about the structure and function of vertebrate cholinesterases, illustrate the molecular diversity and tissue distribution of these enzymes in C. elegans, and discuss to what extent this may represent a paradigm for nematodes in general.

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is currently being used for rapid and reproducible identification of bacteria, viruses and fungi in clinical microbiological laboratories. However, some studies have also reported the use of MALDI-TOF MS for identification of parasites, like Leishmania, Giardia, Cryptosporidium, Entamoeba, ticks and fleas. The present review collates all the information available on the use of this technique for parasites, in an effort to assess its applicability and the constraints for identification/diagnosis of parasites and diseases caused by them. Though MALDI-TOF MS-based identification of parasites is currently done by reference laboratories only, in future, this promising technology might surely replace/augment molecular methods in clinical parasitology laboratories.

We studied patterns of variation in parasite communities of 2 closely related species of Mastomys rodents. These 2 species live in sympatry in South-eastern Senegal, but differ drastically in their habitat choice. We asked (a) whether the host species have the same parasites; (b) whether there is any observable pattern relative to the host species/habitat type in the structure of parasite communities; (c) whether the variability in parasite community for each host species is related to habitat characteristics. We analysed 220 and 264 individuals of each host species, sampled respectively in 10 and 11 trap sites. Twenty parasite taxa were recorded, and the majority were nematodes. Between-host species comparisons showed that helminth communities were slightly more diversified in M. natalensis. Many parasite species were found in both Mastomys. However, various helminth taxa varied in frequency and abundance between host species. Within each host species, helminth diversity, prevalence and/or abundance of some parasites were correlated with habitat or host population factors that may influence parasite life-cycles, such as village structure, or the presence/absence of a pool. Our results suggest that habitat characteristics have a strong impact on helminth community structure.

Objective. RhD-positive subjects are protected against toxoplasmosis-associated impairment of psychomotor performance. Here we searched for RhD-positivity-associated maternal protection against the effects of toxoplasmosis. Methods. In the present retrospective cohort study, we analysed data from 785 (139 RhD-negative) Toxoplasma-free and 194 (27 RhD-negative) Toxoplasma-infected pregnant women. We searched for effects of toxoplasmosis and Rhd-phenotype on maternal weight before pregnancy, pregnancy weight gain, fetal ultrasound data (biparietal diameter, abdominal circumference, femur length) and on birth length and weight. Results. At pregnancy week 16, the RhD-negative mothers with toxoplasmosis gained more weight than others (P<0·001). The difference of about 1600 g remained approximately constant from pregnancy week 16 until the end of pregnancy. Neither toxoplasmosis nor RhD phenotype had any effect on fetal bioparameter data or birth length and weight. Conclusion. The most parsimonious explanation for the observed data is that the RhD-positive phenotype might protect infected subjects against a broad spectrum of detrimental effects of latent toxoplasmosis, including excessive gestational weight gain.

Hosts living on islands carry few parasite species, and the prevalence and intensity of directly transmitted parasites are often higher in insular than in mainland populations. However, it is unclear whether density or other features of insular populations can be responsible for the pattern observed. We compared the parasite richness, prevalence and intensity of parasites between 2 feral populations of cats living either at low density on an island (Kerguelen) or at high density on the mainland (Lyon). Parasite richness was higher in Lyon than in Kerguelen, where only Toxocara cati was found. T. cati egg prevalence was higher in Kerguelen (71·1%) than in Lyon (58·0%). Because cat density cannot explain this pattern, we propose that the low number of parasite species, the diet and/or immunity of cats act to increase prevalence in Kerguelen. Moreover, prevalence, intensity and variance-to-mean ratio increased with age and body mass in Kerguelen whereas, in Lyon, prevalence decreased with age and body mass. We hypothesize that the pattern of exposure differs between populations, and that density-dependent parasite mortality is lower in Kerguelen than in Lyon. We discuss the consequences concerning the influence of parasites on insular host populations.

The 4 species of ruminants (dromedary, zebu cattle, sheep and goat) in arid areas of Mauritania harboured Haemonchus spp. as the most frequent internal parasite. This was a rare situation where the 3 putative species, H. longistipes (dromedary), H. placet (zebu cattle) and H. contortus (sheep and goat) occurred sympatrically. The study was undertaken on hosts slaughtered at the Nouakchott abattoir, on the basis of monthly collection of worms. The environment was very unfavourable to H. placei and unfavourable to H. contortus, as intensity of infection remained low throughout the year, whereas infection in the dromedary was 10 to 20-fold higher. The survival strategies during the long, dry season were different: the surviving stages were either 4th-stage larvae in digesta (dromedaries), 4th-stage larvae either in digesta or mucosae (cattle), or 4th-stage larvae in mucosae and few adults (sheep and goats). The prolificacy of female worms, indicative of the potential to contaminate pastures, was similar for all Haemonchus spp. in the rainy season. H. longistipes behave differently during the pre-rainy season as no increase of prolificacy could be demonstrated as observed in the other species. Traits of vulvar morphology are considered as markers of ecological adaptation and were studied. The knobbed and smooth female morphs (in equal proportions) were the most frequent in H. longistipes, the knobbed morph out-numbered the other morphs in H. placei, and all 3 morphs were present in sheep and goats with the linguiform form being predominant. Genetic characterization of the 3 species was performed by means of Random Amplified Polymorphic DNA (RAPD). Three groups were obtained from analysis of these data: 1 group with individuals of H. contortus, 1 group with individuals of H. placei, and 1 group with individuals of H. longistipes. This indicated that, although the 3 species were valid, H. contortus and H. placei were more similar. Intraspecific variability was 2-fold higher in H. contortus than in the 2 other species. The ecological, morphological and genetical studies showed that H. longistipes, H. placei and H. contortus could be arranged in increasing order of variability.

The melanization of Dirofilaria immitis microfilariae in Armigeres subalbatus haemolymph in vitro is a two-step process. Firstly, the microfilariae are encased in a transparent capsule, then the capsule material is melanized later. Benzamidine HCl and p-amidinophenylmethanesulfonyl fluoride, both serine protease inhibitors, inhibited the deposition of the transparent capsule material and melanization. Diethyldithiocarbamate, a phenoloxidase inhibitor, did not prevent the deposition of the transparent capsule material but it did inhibit melanization. m-Hydroxybenzylhydrazine, a dopa decarboxylase inhibitor, had no inhibitory action on the deposition of the transparent capsule material. However, the time for the transparent capsule to become melanized was delayed due to the presence of m-hydroxybenzylhydrazine in the test system. Immunocytochemical localization showed that prophenoloxidase and/or phenoloxidase was present in the transparent capsule material. These results suggest (1) that prophenoloxidase cascade is essential in the melanization of microfilariae in mosquitoes and its putative activation behaviour is similar to that of other insects and (2) that the deposition of transparent capsule material is a result of the activation of prophenoloxidase by serine proteases and the melanization of the transparent capsule material is due to the presence of active phenoloxidase in capsule.

CBA mice deprived of their T-cells by means of thymectomy and administration of rabbit anti-mouse thymocyte serum before a primary infection of Schistosoma mansoni, failed to resist re-infection to the same extent as immunologically intact controls. However, little difference was made to the degree of resistance to re-infection acquired by thymectomized S. mansoni-infected mice when the anti-thymocyte serum was administered after the primary infection and just before the challenge. Hydrocortisone acetate, when administered to primarily infected mice just before reinfection appeared to reduce the degree of acquired resistance, but the drug also had a schistosomicidal effect on the challenge-derived organisms. An attempt to specifically suppress the acquisition of resistance against S. mansoni by administering serum from homologously infected, resistant donors before and during the course of a primary infection failed, and partial depletion of complement activity with cobra venom factor that was administered just before challenge also failed to affect resistance. Serum obtained from mice with chronic S. mansoni infections and injected intradermally at the site of subsequent administration of a homologous percutaneous challenge infection failed to markedly inhibit maturation of the challenge in the recipient. Recipients of 3 ml of serum from heavily infected donors were also not significantly more resistant to challenge than untreated controls. However, isolated skin from heavily infected mice allowed fewer cercariae to penetrate and emerge transformed as schistosomula than did isolated skin from uninfected controls.

Environmental sex determination in the mermithid nematode Romanomermis culicivorax is examined in the context of parasite reproductive success and population regulation. Experimental results show that the sex ratio of the nematode within its mosquito host (Culex quinquefasciatus) is dependent on parasite density. Sex ratios are biased to females at low parasite burdens and to males at high parasite burdens. Low temperature further enhances female-biased ratios. The net effect of density-dependent sex determination on parasite and host population growth is shown to be critically dependent on the frequency distribution of parasite numbers/host. Mermithid parasite distributions within natural host populations show low degrees of aggregation relative to other helminth species. The population regulation of the parasite is examined with respect to environmental sex determination and parasite-induced host mortalities by means of simple mathematical models of the dynamics of parasite transmission via its life-cycle. The significance of regulatory constraints on population growth are discussed in relation to the use of mermithids as biological control agents of insect pests or disease vectors.