Killing of intramolluscan schistosomes by host haemocytes is mediated by reactive oxygen metabolites. Hence, defence against oxidative damage is essential for the parasite to survive. In this study, expression of three key antioxidant enzymes, superoxide dismutase (EC 1.15.1.1), glutathione peroxidase (EC 1.11.1.9) and glutathione-S-transferase (EC 2.5.1.18) was determined in Schistosoma mansoni miracidia, sporocysts and cercariae. Stage-dependent expression of these enzymes was shown to be regulated at the transcriptional level. Second, the influence on enzyme expression of reactive oxygen species (ROS) and of haemocytes from schistosome-resistant and -susceptible host snails was determined. Generation of ROS by xanthine/xanthine oxidase resulted in increased transcript levels for all three enzymes. Addition of hydrogen peroxide induced a significantly increased expression of GPx and SOD but not GST. Snail haemocytes induced an up-regulation of SOD and GPx at 12 and 18 h post-exposure, respectively. Susceptible haemocytes elicited a stronger induction of transcript expression than resistant haemocytes. After 36–48 h, SOD remained up-regulated in sporocysts encapsulated by haemocytes from susceptible hosts, whereas a down-regulation of SOD and GPx occurred in schistosomes encapsulated by haemocytes from resistant snails. These observations indicate that schistosomes express elevated levels of antioxidant enzymes in interaction with haemocytes from susceptible snail hosts in which they survive. On the other hand, haemocytes of resistant snails may interfere with reactive oxygen detoxification via down-regulation of schistosome antioxidant enzymes, thus shifting the balance towards parasite killing.

An Eimeria acervulina protein fraction was identified which conferred partial protection against an E. acervulina challenge infection. From this fraction a 37 kDa protein was purified and its corresponding cDNA was cloned and shown to encode a lactate dehydrogenase (LDH). Full length cDNAs encoding LDH from two related species, E. tenella and E. maxima, were also cloned. The homology between the primary amino acid sequences of these three Eimeria LDH enzymes was rather low (66–80%), demonstrating an evolutionary divergence. The Plasmodium LDH crystal structure was used to generate a 3D-model structure of E. tenella LDH, which demonstrated that the many variations in the primary amino acid sequences (P. falciparum LDH and E. tenella LDH show only 47% identity) had not resulted in altered 3D-structures. Only a single LDH gene was identified in Eimeria, which was active as a homotetramer. The protein was present at similar levels throughout different parasitic stages (oocysts, sporozoites, schizonts and merozoites), but its corresponding RNA was only observed in the schizont stage, suggesting that its synthesis is restricted to the intracellular stage.

The questing height (i.e. ambush height) of ticks on a plant plays an important role in host selection. To test the hypothesis that the questing height of ticks in a locality had adapted to the body size of the host in that locality, we examined the questing height of nymphs of the ticks, Haemaphysalis longicornis and H. mageshimaensis, at 7 locations in Japan. Sika deer, Cervus nippon, is the primary host of these ticks and there is considerable geographical variation in the body size of sika deer. Multiple regression analysis revealed that the questing height in the field was influenced by the height of the plants and by the body size of deer at a location. However, the questing height of ticks at some locations may have been constrained by the height of the plants and might not be the same as their intrinsic questing height. When ticks were placed in vertical glass tubes in the laboratory, the questing height of ticks from a locality was correlated with the mean body size of deer at that locality. Therefore, the prominent cue determining the questing height of H. longicornis and H. mageshimaensis seems to be the body size of the host deer.

The term ‘data mining’ can be used to describe any process where useful information is extracted from data with a large background of ‘noise’. In the context of a genome project, several stages involve data mining. Amongst the sequence data, ‘signals’ need to be detected that indicate the presence of interesting features. Often this involves differentiating between transcribed and non-transcribed bases to predict coding regions. After detection, defining the roles of these sequences involves sifting through multiple lines of evidence. If these roles are accurately reflected in genome annotation, they can be used by researchers to frame queries and interrogate the data further.

Intergenic region typing by restriction analysis of the ribosomal internal transcribed spacer (ITS) and mini-exon provide diagnostic markers for some Leishmania. Here, we evaluate restriction analysis of these targets for genotyping and phylogenetic analysis within the Leishmania donovani complex (agents of visceral leishmaniasis). Each method was useful for genotyping of both L. donovani complex strains and Old World Leishmania species. The targets produced less robust groups than gp63 intergenic regions, but support the need for re-evaluation of the taxonomy of the L. donovani complex.

The isolation and molecular characterization of the gene coding for L14 ribosomal protein from L. braziliensis is described. There are 2 copies of the gene per haploid genome, repeated in a head-to-tail tandem orientation and located in a single chromosome of approximately 950 kb. Northern blot analyses indicate the presence of a single transcript of 0·95 kb which is up-regulated when parasites reach the stationary growth phase. L. braziliensis L14 gene codes for a 175 amino acid long polypeptide showing 75–83% sequence identity with L14 proteins from trypanosomatids and approximately 25% with its counterparts from higher eukaryotic organisms. L14 ribosomal proteins from trypanosomatids and higher eukaryotes share along their molecules a similar distribution pattern of theoretically functional domains. L. braziliensis L14 recombinant protein is not recognized by sera from cutaneous leishmaniasis patients. Immunization of mice with one dose of L14 recombinant protein and a second dose of L14 protein covalently linked to the HSP70 from Trypanosoma cruzi induces a high antibody level against this L14 protein, which is mostly of the IgG2a subtype, as well as a strong increase in splenocyte proliferation index.

Here we describe extracellular matrix alterations in footpad lesions and draining lymph nodes caused by Leishmania (L.) amazonensis in mouse strains with distinct susceptibilities to this parasite: BALB/c (susceptible), C57BL/6 (intermediate), and DBA/2 (resistant). Changes in ECM were observed mainly in BALB/c mice that, in general, presented tissue damage associated with high parasite burden. Under polarized light, Sirius Red revealed type I collagen that was predominant in the primary lesion in all strains studied at the early phase of infection, but gradually decreased and was replaced by abundant type III collagen fibres in chronic phase lesions. The presence of type III collagen seemed to provide support to inflammatory cells, mainly vacuolated and parasitized macrophages. Laminin expression was not altered during infection by L. (L.) amazonensis in any of the mouse strains studied. Furthermore, the decreased fibronectin expression, in all strains, in areas where amastigotes have been found, indicated that this decline was also not related to the genetic background.

Sex ratio theory posits that the adaptive proportion of male to female gametocytes of a malaria parasite within the vertebrate host depends on the degree of inbreeding within the vector. Gametocyte sex ratio could be phenotypically flexible, being altered based on the infection's clonal diversity, and thus likely inbreeding. This idea was tested by manipulating the clonal diversity of infections of Plasmodium mexicanum in its lizard host, Sceloporus occidentalis. Naive lizards were inoculated with infected blood from a single donor or 3 pooled donors. Donors varied in their gametocyte sex ratios (17–46% male), and sex ratio theory allowed estimation of the clonal diversity within donor and recipient infections. Phenotypic plasticity would produce a correlation between donor and recipient infections for infections initiated from a single donor, and a less female-biased gametocyte sex ratio in recipients that received a mixed blood inoculum (with predicted higher clonal diversity) than recipients receiving blood from a single donor. Neither pattern was observed. Gametocyte sex ratio of most infections ranged from 35 to 42% male, expected if clonal diversity was high for all infections. Alternative explanations are suggested for the observed variation of gametocyte sex ratio among P. mexicanum infections.

Amylopectin is used for carbohydrate storage in different life-stages of a number of apicomplexan parasites. We have performed an ultrastructural analysis of amylopectin granules from the oocyst residual body and sporozoites of Cryptosporidium parvum. Amylopectin granules were studied in situ and after isolation from ‘French’ press disrupted parasites, by conventional transmission electron microscopy (TEM) of sectioned oocysts and various negative staining and cryoelectron microscopy techniques. Within the membrane-enclosed oocyst residuum large amylopectin granules (0·1–0·3 μm) can be found besides a characteristic large lipid body and a crystalline protein inclusion. Smaller granules were detected in sectioned sporozoites. Negative staining of isolated amylopectin granules revealed some ultrastructural features not readily visible in sectioned material. The large amylopectin granules had a smooth surface with a ‘ball of string’-like inner structure. Granules isolated from sporozoites were more irregularly shaped and showed a rod-like particulate composition. With the exception of α-amylase, which led to some degree of damage of the surface of the particles, treatment of amylopectin granules with other glycohydrolases had little effect on the overall structure. However, granules adhered to one another. Only when the granules were boiled did the ‘ball of string’ structure gradually dissolve.

Among the variety of virulence factors of Entamoeba histolytica, an adherence lectin (Gal/GalNAc, 260 kDa) is known to mediate colonization and subsequent host responses. Gal/GalNAc lectin is universally recognized by the immune sera of patients with amoebic liver abscess. It plays a crucial role in cytolysis and phagocytosis of human and rat colonic mucin glycoproteins. The objective of the present study was to elucidate the role of antioxidants in E. histolytica Gal/GalNAc lectin-induced signals in the target epithelial cells. We have attempted to define a pathway in target cells, Henle-407 cells (human intestinal epithelial cell line), that could link this immunodominant antigen to a known biological pathway for target cell activation and triggering of subsequent disease pathology/parasite survival. Since several workers have demonstrated that cAMP and cGMP may act as important cellular signals for altering ion transport, so in the present study, cAMP and cGMP levels were measured in Henle-407 cells which showed significant increase at 15 min after stimulation. Elevated cAMP and cGMP levels are implicated in altered electrolyte transport and conductance. Results showed that there were increased levels of ROS and RNI which led to reduced activities of antioxidant enzymes – catalase, superoxide dismutase and glutathione peroxidase. Despite the increased glutathione (reduced) levels, the enzymes were not able to combat the damage caused by ROS and RNI. Thus, there was an increased local concentration of the free radicals and reduced activities of all the three enzymes which could damage the target cell in terms of cytoskeleton and permeability changes.

The fresh-water crustacean Daphnia magna may acquire an infection with the microsporidium Octosporea bayeri either by ingesting spores from the water (horizontally), or directly from its mother (vertically). Due to differences in the time and mechanisms of transmission, horizontal and vertical infections may lead to differences in the growth of the parasite within the host. This may influence parasite virulence, transmission to new hosts, and, consequently, epidemiology and evolution. Here we describe the within-host dynamics of 3 spore-types of O.bayeri from infections that were acquired either horizontally or vertically. In all treatments the number of spores increased exponentially until spore density reached a plateau, suggesting density-dependent within-host growth. The spore types seen differ in their growth dynamics, suggesting different roles in the parasite life-cycle. Horizontally-infected hosts harboured significantly fewer spores than vertically-infected hosts. Further, host survival was affected by infection route, with mortality being higher in horizontal infections than in vertical infections. Our results suggest that different routes of infection have an immediate effect on within-host parasite growth and thus on parasite fitness and epidemiology.

Eimerian parasites display a biologically interesting range of phenotypic variation. In addition to a wide spectrum of drug-resistance phenotypes that are expressed similarly by many other parasites, the Eimeria spp. present some unique phenotypes. For example, unique lines of Eimeria spp. include those selected for growth in the chorioallantoic membrane of the embryonating hens egg or for faster growth (precocious development) in the mature host. The many laboratory-derived egg-adapted or precocious lines also share a phenotype of a marked attenuation of virulence, the basis of which is different as a consequence of the in ovo or in vivo selection procedures used. Of current interest is the fact that some wild-type populations of Eimeria maxima are characterized by an ability to induce protective immunity that is strain-specific. The molecular basis of phenotypes that define Eimeria spp. is now increasingly amenable to investigation, both through technical improvements in genetic linkage studies and the availability of a comprehensive genome sequence for the caecal parasite E. tenella. The most exciting phenotype in the context of vaccination and the development of new vaccines is the trait of strain-specific immunity associated with E. maxima. Recent work in this laboratory has shown that infection of two inbred lines of White Leghorn chickens with the W strain of E. maxima leads to complete protection to challenge with the homologous parasite, but to complete escape of the heterologous H strain, i.e. the W strain induces an exquisitely strain-specific protective immune response with respect to the H strain. This dichotomy of survival in the face of immune-mediated killing has been examined further and, notably, mating between a drug-resistant W strain and a drug-sensitive H strain leads to recombination between the genetic loci responsible for the specificity of protective immunity and resistance to the anticoccidial drug robenidine. Such a finding opens the way forward for genetic mapping of the loci responsible for the induction of protective immunity and integration with the genome sequencing efforts.

The factors responsible for the reactivation of a Neospora caninum latent infection are unknown, but it is postulated that the maternal immune response could be altered during pregnancy. The immune response was investigated in N. caninum chronically infected mice during successive pregnancies as well as in non-pregnant infected mice and mice infected when pregnant. Vertical transmission was demonstrated in chronically infected mice after the first pregnancy but the rate of fœtal infection fell after further pregnancies. Non-pregnant chronically infected mice showed a marked specific proliferative response and an IgG2a isotype preferential secretion. During the course of the first pregnancy, no significant modification of the immune response was recorded. After 2 successive pregnancies, the specific cellular response showed a significant fall whereas Th2 cytokine mRNA expression was noted. At the same time, IgG1 secretion increased to reach the IgG2a level. At the third delivery, a partial restoration of the proliferative response was observed. The reactivation of N. caninum chronic infection during pregnancy does not seem to be consecutive to an immunodepression. Nevertheless, pregnancy could favour parasite multiplication in utero after an occasional spontaneous release of bradyzoites.

Previous studies have indicated that SAG1, the major surface molecule of the protozoan parasite Toxoplasma gondii, is an important attachment ligand for the host cell. However, the research data that supports this claim comes largely from studies investigating tachyzoite binding, and not SAG1 binding per se. In this study we successfully developed an in vitro attachment assay to directly evaluate the mechanism of SAG1-host cell binding. Competition experiments were then performed using SAG1 that had been pre-treated with the neoglycoprotein BSA-glucosamide or with antibody. Soluble BSA-glucosamide blocked SAG1 attachment to MDBK cells in a dose-dependent manner, implying that SAG1 binding is mediated, in part, via attachment to host cell surface glucosamine. Interestingly, pre-incubation of SAG1 in polyclonal sera from chronically infected mice failed to block binding. This challenges the assumption that anti-SAG1 antibodies block parasite attachment through the masking of SAG1 host cell binding domains. Taken together, this evidence presents new strategies for understanding SAG1-mediated attachment.

Phylogenetic relationships within the Capsalidae (Monogenea) were examined using large subunit ribosomal DNA sequences from 17 capsalid species (representing 7 genera, 5 subfamilies), 2 outgroup taxa (Monocotylidae) plus Udonella caligorum (Udonellidae). Trees were constructed using maximum likelihood, minimum evolution and maximum parsimony algorithms. An initial tree, generated from sequences 315 bases long, suggests that Capsalinae, Encotyllabinae, Entobdellinae and Trochopodinae are monophyletic, but that Benedeniinae is paraphyletic. Analyses indicate that Neobenedenia, currently in the Benedeniinae, should perhaps be placed in a separate subfamily. An additional analysis was made which omitted 3 capsalid taxa (for which only short sequences were available) and all outgroup taxa because of alignment difficulties. Sequence length increased to 693 bases and good branch support was achieved. The Benedeniinae was again paraphyletic. Higher-level classification of the Capsalidae, evolution of the Entobdellinae and issues of species identity in Neobenedenia are discussed.

We characterized 14 trypanosome isolates from sylvatic mammals (9 from primates, 1 from sloth, 2 from anteaters and 2 from opossum) plus 2 human isolates of Brazilian Amazon. These isolates were proven to be Trypanosoma rangeli by detection of metacyclic trypomastigotes in the salivary glands of triatomines and by a specific PCR assay. Polymorphism determined by randomly amplified polymorphic DNA (RAPD) revealed that most (12) of the Brazilian T. rangeli isolates from the Amazon differed from those of other geographical regions, thus constituting a new group of T. rangeli. Four Brazilian isolates clustered together with a previously described group (A) that was described as being composed of being isolates from Colombia and Venezuela. Isolates from Panama and El Salvador form another group. The isolate from Southern Brazil did not cluster to any of the above-mentioned groups. This is the first study that assesses the genetic relationship of a large number of isolates from wild mammals, especially from non-human primates. A randomly-amplified DNA fragment (Tra625) exclusive to T. rangeli was used to develop a PCR assay able to detect all T. rangeli groups.

The behaviour and development of Elasmosoma sp., near pergandei Ashm. (Neoneurinae: Braconidae: Hymenoptera), a parasite of the ant, Formica obscuriventris clivia Creighton, was studied in a coastal sand dune habitat in central Oregon over a 2-year period. Female wasps oviposited into the abdomen of major worker ants after alighting briefly on the host. Embryonic development of the wasp occurred inside the serosal membrane or trophamnion of the egg in the abdomen of the ant host. First instar wasp larvae possessed a large head capsule with falcate mandibles, 11 ventral body lobes, an elongate tail and a dorsally located anus. Second instar larvae were unspecialized and lacked the large head capsule, elongate tail and paired ventral body lobes. Third instar larvae were hymenopteriform with a distinct head capsule. Cocoon formation and adult emergence is described. Observations on the percentage parasitism and altered behaviour of parasitized ants are presented. The association between neoneurine wasps and ants is a well-balanced system that has been in existence for at least 40 million years.

Toxoplasma gondii is the aetiological agent of toxoplasmosis and is the most frequent and best known of the parasitic diseases. In the United States, a serological survey from the Third National Health and Nutrition Examination Survey found that an estimated 23% of adolescents and adults have laboratory evidence of infection with T. gondii. Although toxoplasmosis is asymptomatic or shows self-limited symptoms in adults, in pregnant women infections can cause severe health problems to the fetus if the parasites are transmitted. Also, in immunodeficient patients, chronic infection with T. gondii can reactivate and produce encephalitis, which is frequently lethal. In addition, in veterinary medicine, T. gondii infection is of economic importance due to abortion and neonatal loss in sheep and goats. Recently, the development of vaccines against toxoplasmosis has progressed considerably. The live attenuated S48 strain of Toxoplasma has been broadly used for veterinary purposes. DNA vaccines containing the full-length of SAG1/P30, ROP2 or ROP 1 genes have proved to be a promising candidate to induce protection against toxoplasmosis. Viral vectors have proved to be the best candidates for vaccination in different diseases. A recombinant Herpes virus carrying the ROP2 gene is able to induce protective immunity in cats. In the present work we describe the potential of the MVA ROP2 recombinant vaccinia virus as a vaccine against toxoplasmosis. MVA ROP2 induces antibodies against the ROP2 protein in similar amount and types as the thermo-sensible strain ts-4 of T. gondii, which is able to fully protect mice against challenge with the virulent RH strain of T. gondii. Also, the life-span of mice is increased in MVA ROP2 vaccinated animals. We conclude that MVA ROP2 vaccine can possibly generate an immune response, which could be useful in protection against toxoplasmosis.

In this study, a single-step duplex polymerase chain reaction procedure was developed for rapid, specific and sensitive identification of Entamoeba histolytica and for its diagnostic differentiation from E. dispar. Specific oligonucleotide primers were combined for the amplification of a cysteine proteinase 5 gene target sequence of 242 bp, present only in E. histolytica. Additionally, another oligonucleotide primer pair for both the E. histolytica and E. dispar actin gene target of 300 bp was designed to amplify only from amoebae DNA. The PCR developed was specific and efficiently identified and differentiated these parasites from each other in either cultured parasites or from stool material.

In total, 61 Chilean isolates of Trypanosoma cruzi, were analysed using schizodeme and Southern analysis, using as probes the highly variable regions of minicircles from cloned parasites. Isolates were collected and amplified from domestic and wild triatomines, and from infected subjects in all the endemic areas of Chile. Three major parasite genotypes could be detected in the domestic transmission cycle, whilst 1 major T. cruzi genotype is circulating in the wild transmission cycle. Schizodeme analysis suggested that T. cruzi isolates are mixed populations, whereas the Southern analyses detected only 3 mixed isolates using 4 selected minicircle segments as probes.