Past and more recent research has examined the ultrastructure, metabolism, cell biology, genomics and post-genomics of schistosome schistosomula. These areas are considered and discussed in this review with particular emphasis on (1) the early migration phases through the host, (2) interaction of the host immune response with the parasite surface, (3) glucose uptake mechanisms, and (4) defining the transcriptional profiles of lung-stage schistosomula compared with other developmental stages using microarrays. The microarray profiling studies suggest caution is required when considering the use of schistosomes obtained by in vitro means for molecular or biochemical studies.

Signal transduction molecules play key roles in the regulation of developmental processes, such as morphogenesis, organogenesis and cell differentiation in all organisms. They are organized into ‘pathways’ that represent a coordinated network of cell-surface receptors and intracellular molecules, being involved in sensing environmental stimuli and transducing signals to regulate or modulate cellular processes, such as gene expression and cytoskeletal dynamics. A particularly important group of molecules implicated in the regulation of the cytoskeleton for the establishment and maintenance of cell polarity is the PAR proteins (derived from partition defective in asymmetric cell division). The present article reviews salient aspects of PAR proteins involved in the early embryonic development and morphogenesis of the free-living nematode Caenorhabditis elegans and some other organisms, with an emphasis on the molecule PAR-1. Recent advances in the knowledge and understanding of PAR-1 homologues from the economically important parasitic nematode, Haemonchus contortus, of small ruminants is summarized and discussed in the context of exploring avenues for future research in this area for parasitic nematodes.

Malaria parasites in the genus Plasmodium are now placed within 11 subgenera based on morphology under the light microscope, life-history traits, and host taxon. The phylogenetic significance of these characters, however, is problematic because the observed variation could be homoplasious. Using Plasmodium infections found in 2632 birds of many avian families collected in the USA, and several samples from other locations, we compared identifications to subgenus based on morphology in blood smears with a 2-gene molecular phylogeny (the first for avian Plasmodium) to determine if the 5 avian Plasmodium subgenera represent monophyletic groups. Phylogenetic trees recovered by parsimony, likelihood, and Bayesian methods presented nearly identical topologies. The analysis allowed testing the hypothesis of monophyly for the subgenera. Monophyly of the subgenera Haemamoeba, Huffia, and Bennettinia was supported by the analysis. The distinctive morphology of Haemamoeba species appears to have evolved once. Most samples identified to Novyella also fell within a monophyletic clade with the exception of 2 samples that fell basal to all other avian Plasmodium. Samples of the subgenus Giovannolaia did not form a monophyletic group. Thus, the characters used by parasitologists for over a century to define subgenera of Plasmodium vary in their phylogenetic significance.

Here we have studied phospholipase A1 (Plase A1) from Trypanosoma cruzi infective stages and it's possible role regarding the interaction with mammalian host cells. Plase A1 was mainly detected as a membrane-bound activity in the infective amastigote and trypomastigote stages, being remarkably higher with respect to the non-infective epimastigotes. It is noteworthy that only the infective stages secreted Plase A1. Moreover, along the differentiation process from epimastigotes into metacyclic trypomastigotes, the secreted enzyme activity increased simultaneously with the appearance of metacyclic forms, as expected. Since this enzyme is predominantly membrane-associated and secreted by the infective stages, Vero cell lipid profile modifications were analysed after interaction with either intact infective parasites or purified T. cruzi Plase A1. Significant changes in Vero cell lipid composition were observed, with the appearance of free fatty acids, diacylglycerol and lysophosphatidylcholine. Concomitantly with the generation of second lipid messengers, host cell protein kinase C activation was demonstrated. These results indicate that T. cruzi Plase A1 could play a critical role in the early events of parasite-host cell interaction that precede invasion.

During the acute phase of Trypanosoma cruzi infection, strong haematological and immune system alterations are observed. The parasite expresses trans-sialidase, a virulence factor responsible for the sialylation of its surface glycoconjugates. This enzyme is also shed to the bloodstream where it is associated with immune system alterations triggered during the infection. During experimental and human infections, the host elicits antibodies able to neutralize the enzyme activity that would be responsible for restricting systemic trans-sialidase to the early steps of the infection, when major immune alterations are induced. The actual relevance of these antibodies was tested by passive transference of monoclonal neutralizing antibodies in acute infection models displaying extreme sensitivity to the infection. Mice were inoculated with virulent parasite strains that induce high parasitaemia, early mortality and strong immune tissue abnormalities. The trans-sialidase-neutralizing antibodies were able to preserve B cell areas both in ganglia and spleen as well as the thymus architecture even in these extreme models. Although no differences between control and treated mice regarding animal survival were found, a major role for the humoral response in controlling the damage of the immune system induced by a systemically distributed virulence factor was defined in an infection with a eukaryotic pathogen.

Leishmania mutants have contributed greatly to extend our knowledge of this parasite's biology. Here we report the use of the mariner in vitro transposition system as a source of reagents for shuttle mutagenesis and targeted disruption of Leishmania genes. The locus-specific integration was achieved by the disruption of the subtelomeric gene encoding a DNA-directed RNA polymerase III subunit (RPC2). Further inactivation of RPC2 alleles required the complementation of the intact gene, which was transfected in an episomal context. However, attempts to generate a RPC2 chromosomal null mutant resulted in genomic rearrangements that maintained copies of the intact locus in the genome. The maintenance of the RPC2 chromosomal locus in complemented mutants was not mediated by an increase in the number of copies and did not involve chromosomal translocations, which are the typical characteristics of the genomic plasticity of this parasite. Unlike the endogenous locus, the selectable marker used to disrupt RPC2 did not display a tendency to remain in its chromosomal location but was targeted into supernumerary episomal molecules.

Non-availability of adult worms from living hosts remains a key problem in population genetic studies of schistosomes. Indirect sampling involving passage through laboratory animals presents significant ethical and practical drawbacks, and may result in sampling biases such as bottlenecking processes and/or host-induced selection pressures. The novel techniques reported here for sampling, storage and multi-locus microsatellite analysis of larval Schistosoma mansoni, allowing genotyping of up to 7 microsatellite loci from a single larva, circumvent these problems. The utility of these assays and the potential problems of laboratory passage, were evaluated using 7 S. mansoni population isolates collected from school-children in the Hoima district of Uganda, by comparing the associated field-collected miracidia with adult worms and miracidia obtained from a single generation in laboratory mice. Analyses of laboratory-passaged material erroneously indicated the presence of geographical structuring in the population, emphasizing the dangers of indirect sampling for population genetic studies. Bottlenecking and/or other sampling effects were demonstrated by reduced variability of adult worms compared to their parent field-collected larval samples. Patterns of heterozygote deficiency were apparent in the field-collected samples, which were not evident in laboratory-derived samples, potentially indicative of heterozygote advantage in establishment within laboratory hosts. Genetic distance between life-cycle stages in the majority of isolates revealed that adult worms and laboratory-passaged miracidia clustered together whilst segregating from field miracidia, thereby further highlighting the utility of this assay.

The study was aimed at developing better orally active albendazole (ALB) formulations. Six formulations (ALB-1 to ALB-6) were prepared and tested against Brugia malayi in Mastomys coucha and jird (Meriones unguiculatus) at 200 mg/kg, orally, for 5 consecutive days. The anti-filarial efficacy was assessed against microfilariae (mf), adult worms and female reproductive potential. Three of the 6 ALB formulations showed greatly improved female worm sterilizing potential (ALB-1: 90%; ALB-3: 63%; ALB-4: 77% of untreated control) in B. malayi – M. coucha model. Sterilization efficacy of ALB-1 was also better than that shown by pure-ALB (P<0·001) or its marketed tablet formulation, Zentel (P<0·01), while that of ALB-4 was better than pure-ALB (P<0·05). The activity of ALB-3, pure-ALB and Zentel was, however, comparable. ALB-1 also showed late microfilaricidal activity with a maximum of 78% fall in microfilarial count. In contrast, neither the pure ALB nor Zentel showed any microfilaricidal activity. In the jird – B. malayi model, ALB-1 and ALB-4 showed marginal sterilizing efficacy whereas pure ALB or Zentel were ineffective. In conclusion the anti-filarial efficacy of ALB-1 was found to be superior to pure-ALB or Zentel.

Polistes dominulus are social wasps which are the host of the strepsipteran endoparasite Xenos vesparum. In the hibernating phase, unparasitized and parasitized wasps leave natal nests and aggregate together in sheltered quarters. In aggregations, wasps are socially active, and some individuals perform helping behaviour. Here we investigated if castrated parasitized wasps perform worker tasks in mixed aggregations. Moreover, by gas chromatography and mass spectrometry, we examined the cuticular hydrocarbons of unparasitized and parasitized wasps to evaluate if the infection alters the composition of cuticular waxes that are recognition cues in social insects. In clusters, infected females do not perform helping behaviour and they are less active than unparasitized wasps. Cuticular hydrocarbons are slightly differentiated between unparasitized and parasitized wasps but, generally, unparasitized wasps are more similar to wasps infected by Xenos females compared to wasps infected by Xenos males. Wasps infected by Xenos males do not usually survive the winter. This chemical similarity is probably a consequence of the similar physiological condition of unparasitized and female-affected Polistes wasps. At this stage, it is difficult to affirm whether these modifications are a true parasite manipulation or a consequence of infection.

Multi-drug-resistant gastrointestinal nematode parasite populations are becoming more and more prevalent. Since anthelmintic treatments are of limited effectiveness, one solution could be to replace the anthelmintic-resistant population by a susceptible population, in order to re-establish the possibility of drug-based anthelmintic control. We investigated this substitution strategy in 4 paddocks of 0·7 ha, each of which was seeded with a benzimidazole-resistant Teladorsagia circumcincta population. The proportion of benzimidazole-resistant worms in these paddocks ranged from 20% to 89%. A 2-step replacement was performed: first, the paddocks were not grazed for 6 months (from December to July), and then the grass was cut to eliminate any residual infective larvae, before contaminating each of the paddocks with 10 seeder lambs experimentally infected with a benzimidazole-susceptible strain of T. circumcincta (from July to November). At the end of the experiment, all the populations on the 4 paddocks were phenotypically benzimidazole-susceptible, but genotyping indicated that 2 populations harboured 1% and 3% resistant worms respectively. This study demonstrates that nematode replacement is feasible in temperate areas, using semi-intensive stock management, even when the initial levels of benzimidazole-resistance are very high. Further research should next assess replacing the whole community to cope with the species diversity observed under field conditions.

This study compared the prevalence and intensity of infections of helminths in 2 chicken breeds in Vietnam, the indigenous Ri and the exotic Luong Phuong. Also, possible correlations with the Major Histocompatibility Complex (MHC) were tested. The most prevalent helminths were Ascaridia galli, Heterakis beramporia, Tetrameres mothedai, Capillaria obsignata, Raillietina echinobothrida and Raillietina tetragona. Differences in prevalence and intensity of infection were found between the 2 breeds. Comparing the 2 groups of adult birds, Ri chickens were observed to have higher prevalence and infection intensities of several species of helminths, as well as a higher mean number of helminth species. In contrast, A. galli and C. obsignata were shown to be more prevalent in Luong Phuong chickens. Furthermore, an age-dependent difference was indicated in the group of Ri chickens in which the prevalence and the intensity of infection was higher for the adult than the young chickens for most helminths. The most notable exception was the significantly lower prevalence and intensities of A. galli in the group of adult chickens. In contrast, the prevalence and intensity were very similar in both age groups of Luong Phuong chickens. Using a genetic marker located in the MHC, a statistically significant correlation between several MHC haplotypes and the infection intensity of different helminth species was inferred. This is the first report of an association of MHC haplotype with the intensity of parasite infections in chickens.

In order to elucidate mechanisms underlying snail/echinostome compatibility, numerous molecular studies comparing transcripts and proteins of Biomphalaria glabrata susceptible or resistant to Echinostoma caproni were undertaken. These studies focused on plasma and haemocytes of the two strains and revealed that some transcripts and/or proteins were differentially expressed between strains. The aim of the present study was to develop a complementary transcriptomic approach by constructing subtractive libraries. This work revealed some candidate transcripts already identified in previous studies (calcium-binding proteins and glycolytic enzymes) as well as novel candidate transcripts that were differentially represented between strains of B. glabrata. Among these newly identified genes, we revealed several genes potentially involved in immune processes encoding proteases, protease inhibitors, a lectin, an aplysianin-like molecule, and cell adhesion molecules.

The monogenean ectoparasite, Gyrodactylus salaris Malmberg, 1957, has had a devastating effect on wild Atlantic salmon (Salmo salar) since its introduction to Norway in the mid-1970s. In Lake Pålsbufjorden, southern Norway, upstream of the stretches of the River Numedalslågen with anadromous Atlantic salmon, a resident Arctic charr (Salvelinus alpinus) population has been reported to be infected with G. salaris which is viable in the absence of its normal host, the Atlantic salmon. Currently, there is no record of G. salaris infecting Atlantic salmon in the downstream sections of the River Numedalslågen. We studied experimentally the infectivity and reproductive capacity of G. salaris from Lake Pålsbufjorden on wild and hatchery-reared Atlantic salmon as well as on Arctic charr and rainbow trout (Oncorhynchus mykiss). Arctic charr and rainbow trout were moderately susceptible, whereas the Atlantic salmon stocks from River Numedalslågen and River Drammenselva were innately resistant to only slightly susceptible. Thus, the G. salaris from Arctic charr in Lake Pålsbufjorden is considered non-pathogenic to Atlantic salmon. This is the first observation of variation in host preference among Norwegian G. salaris populations. The observed differences in virulence between G. salaris populations could have important consequences for the international legislation and management of Atlantic salmon.

Transmission of parasites may be mediated by their habitat, consisting of abiotic and biotic components. I investigated the effect of 2 important habitat components in intertidal ecosystems, tidal level (abiotic) and density of upstream hosts (biotic), on the transmission of trematode cercariae to cockle (Cerastoderma edule) hosts. A field survey showed no general trend in metacercarial loads of cockles regarding tidal level but species-dependent reactions. Parasites originating from Littorina littorea (Himasthla elongata, Renicola roscovita) showed highest infection levels in the low intertidal while parasites originating from Hydrobia ulvae (H. continua, H. interrupta) showed highest infection levels in the mid-intertidal. This reflected the density of upstream hosts at both tidal levels and positive relationships between the density of upstream hosts and metacercarial load in cockles suggested the biotic habitat component to be the dominant factor in transmission. This was confirmed by a field experiment, manipulating tidal level and the density of infected upstream snail hosts. While tidal level had no significant effect on the number of metacercariae of H. elongata acquired by cockles, the effect of upstream host density was strong. In conclusion, although tidal level usually is a very important abiotic habitat component in intertidal ecosystems leading to conspicuous zonation patterns in free-living organisms, it seems of minor importance for trematode transmission. In contrast, the biotic component upstream host density is suggested to be the dominant predictor for trematode transmission to second intermediate hosts. Assessing the relative importance of abiotic and biotic habitat components in transmission is vital for the understanding of transmission processes in the field.

Stepek, G., Lowe A. E., Buttle D. J., Duce I. R. and Behnke J. M. (2007). Anthelmintic action of plant cysteine proteinases against the rodent stomach nematode, Protospirura muricola, in vitro and in vivo. Parasitology134, 103–112 (Published online 11 October 2006. doi:10.1017/S0031182006001302)

The authors of the above article regret that several errors appear in their published paper:

On Page 105: In the methods section entitled “In vivo assessment of anthelmintic efficacy of plant cysteine proteinases”, the sentence:

‘Five grams of papaya latex were mixed with 8 ml of sterile distilled water (dH2O), filtered, and the amount of active enzyme present was measured, by active-site titration, to be 331 nmol’

should read:

‘Five grams of papaya latex were mixed with 8 ml of sterile distilled water (dH2O), filtered, and the amount of active enzyme present was measured, by active-site titration, to be 13·24 micromol’

And the sentence:

‘Each group of mice received a different treatment: 0·2 ml of papaya latex alone (containing 8 nmol active enzyme), …’

should read:

‘Each group of mice received a different treatment: 0·2 ml of papaya latex alone (containing 331 nmol active enzyme), …’

On Page 110: In column 2, line 5, the sentence:

‘The amount of active enzyme administered in each dose (8 nmol) is based …’

should read:

‘The amount of active enzyme administered in each dose (331 nmol) is based …’

And on lines 10–15, the sentence:

‘Assuming the volume of a mouse stomach to be 1 ml and the enzyme to be present throughout the stomach at equal dilution, the concentration of enzyme would be in the order of 8 microM, which is somewhat lower than the in vitro concentrations.’

Should read:

Assuming the volume of a mouse stomach to be 1 ml and the enzyme to be present throughout the stomach at equal dilution, the concentration of enzyme would be in the order of 330 microM, which is about an order of magnitude higher than effective in vitro concentrations. A possible reason for the …’