Nematodes of the genus Strongyloides parasitize the small intestines of vertebrates. In addition to a parasitic life-cycle, which is generally considered to be parthenogenetic, Strongyloides can also have a facultative, free-living generation involving male and female worms. The purpose of the present article was to review the literature on the modes of reproduction, the routes of development in the two generations of Strongyloides, discuss the controversial opinions in the literature regarding these aspects and point to new opportunities for addressing key questions in relation to the biology of reproduction of members of the genus employing genetic and genomic tools.

Cryptosporidium parvum is an intracellular protozoan parasite belonging to the phylum Apicomplexa, and a major cause of waterborne gastroenteritis throughout the world. Invasive zoites of apicomplexan parasites, including C. parvum, are thought to have characteristic organelles on the apical apex; however, compared with other parasites, the cytoskeletal ultrastructure of C. parvum zoites is poorly understood. Thus, in the present study, we ultrastructurally examined C. parvum sporozoites using electron microscopy to clarify the framework of invasive stages. Consequently, at the apical end of sporozoites, 3 apical rings and an electron-dense collar were seen. Two thick central microtubules were seen further inside sporozoites and extended to the posterior region. Using anti-α and -β tubulin antibodies generated from sea urchin and rat brain, both antibodies cross-reacted at the apical region of sporozoites in immunofluorescent morphology. The molecular mass of C. parvum α tubulin antigen was 50 kDa by Western blotting and the observed apical cytoskeletal structures were shown to be composed of α tubulin by immunoelectron microscopy. These results suggested that C. parvum sporozoites were clearly different in their cytoskeletal structure from those of other apicomplexan parasites.

Understanding genetic relationships amongst the life-history traits of parasites is crucial for testing hypotheses on the evolution of virulence. This study therefore examined variation between parasite isolates (the bacterium Pasteuria ramosa) from the crustacean Daphnia magna. From a single wild-caught infected host we obtained 2 P. ramosa isolates that differed substantially in the mortality they caused. Surprisingly, the isolate causing higher early mortality was, on average, less successful at establishing infections and had a slower growth rate within hosts. The observation that within-host replication rate was negatively correlated with mortality could violate a central assumption of the trade-off hypothesis for the evolution of virulence, but we discuss a number of caveats which caution against premature rejection of the trade-off hypothesis. We sought to test if the characteristics of these parasite isolates were constant across host genotypes in a second experiment that included 2 Daphnia host clones. The relative growth rates of the two parasite isolates did indeed depend on the host genotype (although the rank order did not change). We suggest that testing evolutionary hypotheses for virulence may require substantial sampling of both host and parasite genetic variation, and discuss how selection for virulence may change with the epidemiological state of natural populations and how this can promote genetic variation for virulence.

Vole tuberculosis (TB; Mycobacterium microti) is an understudied endemic infection. Despite progressing slowly, it causes severe clinical pathology and overt symptoms in its rodent host. TB was monitored for 2 years in wild field voles in Kielder Forest, UK. The prevalence of characteristic cutaneous TB lesions was monitored longitudinally at 4 sites, with individuals live-trapped and repeatedly monitored. A prevalence of 5·2% of individuals with lesions was recorded (n=2791). In a cross-sectional study, 27 sites were monitored bi-annually, with TB assessed by post-mortem examination for macroscopic lesions, and by culture and histopathology. Seventy-nine voles (10·78%; n=733) were positive for mycobacteria, with the highest prevalence in spring (13·15%; n=327). TB prevalence varied, with between 0% and 50% of voles infected per site. Prevalence increased with age (mass), and apparent seasonality was due to a higher proportion of older animals in spring. Survival analysis supported this result, with cutaneous lesions only manifesting in the advanced stages of infection, and therefore only being found on older voles. The body condition of individuals with lesions declined at the time when the lesion was first recorded, when compared to individuals without lesions, suggesting there may be an acute phase of infection during its advanced stage. Although predicted survival following the appearance of a cutaneous lesion was lower than for uninfected individuals, this was not significant.

Leishmania (Viannia) braziliensis and L. (V.) peruviana are two parasite species characterized by a very different pathogenicity in humans despite a high genetic similarity. We hypothesized previously that L. (V.) peruviana would descend from L. (V.) braziliensis and would have acquired its ‘peruviana’ character during the southward colonization and adaptation of the transmission cycle in the Peruvian Andes. In order to have a first appreciation of the differences in virulence between both species, we evaluated an in vitro and in vivo model for experimental infection. A procedure was adapted to enrich culture forms in infective stages and the purified metacyclics were used to infect macrophage cell lines and golden hamsters. The models were tested with 2 representative strains of L. (V.) braziliensis from cutaneous and mucosal origin respectively and 2 representative strains of L. (V.) peruviana from Northern and Southern Peru respectively. Our models were reproducible and sensitive enough to detect phenotypic differences among strains. We showed in vitro as well as in vivo that the L. (V.) braziliensis was more infective than L. (V.) peruviana. Furthermore, we found that in vitro infectivity patterns of the 4 strains analysed, were in agreement with the geographical structuring of parasite populations demonstrated in our previous studies. Further work is needed to confirm our results with more strains of different geographical origin and their specific clinical outcome. However, our data open new perspectives for understanding the process of speciation in Leishmania and its implications in terms of pathogenicity.

A Leishmania (Leishmania) amazonensis ATP diphosphohydrolase isoform was partially purified from plasma membrane of promastigotes by preparative non-denaturing polyacrylamide gel electrophoresis. SDS-PAGE followed by Western blots developed with polyclonal anti-potato apyrase antibodies identified diffuse bands of about 58–63 kDa, possibly glycosylated forms of this protein. By ELISA technique, a significantly higher total IgG antibody level against potato apyrase was found in serum from promastigote-infected mice, as compared to the uninfected mice, confirming both the existence of shared epitopes between the parasite and vegetable proteins, and the parasite ATP diphosphohydrolase antigenicity. By Western blotting, serum from amastigote-infected BALB/c mice recognizes both potato apyrase and this antigenic ATP diphosphohydrolase isoform isolated from promastigotes, suggesting that it is also expressed in the amastigote stage. The infection monitored along a 90-day period in amastigote-infected mice showed reactivity of IgG2a antibody in early steps of infection, while the disappearance of the IgG2a response and elevation of IgG1 antibody serum levels against that shared epitopes were associated with the progression of experimental leishmaniasis. This is the first observation of the antigenicity of a L. (L.) amazonensis ATP diphosphohydrolase isoform, and of the ability of cross-immunoreactivity with potato apyrase to differentiate serologically stages of leishmaniasis in infected mice.

Molecular interplay during snail-schistosome interactions is poorly understood and there is much to discover concerning the effect of snail host molecules on molecular processes in schistosomes. Using the Biomphalaria glabrata – Schistosoma mansoni host-parasite system, the effects of exposure to haemolymph, derived from schistosome-resistant and susceptible snail strains, on protein tyrosine phosphorylation in miracidia have been investigated. Western blotting revealed several tyrosine phosphorylated proteins in this larval stage. Exposure of miracidia to haemolymph from susceptible snails for 60 min resulted in a striking, 5-fold, increase in the tyrosine phosphorylation of a 56 kDa (p56) S. mansoni protein. In contrast, haemolymph from resistant snails had little effect on protein tyrosine phosphorylation levels in miracidia. Confocal microscopy revealed that tyrosine phosphorylation was predominantly associated with proteins present in the tegument. Finally, treatment of miracidia with the tyrosine kinase inhibitor genistein significantly impaired their development into primary sporocysts. The results open avenues for research that focus on the potential importance of phospho-p56 to the outcome of schistosome infection in snails, and the significance of protein tyrosine kinase-mediated signalling events to the transformation of S. mansoni larvae.

We have previously reported that genetic immunization with Tc13Tul antigen of Trypanosoma cruzi, the aetiological agent of Chagas' disease, triggers harmful effects and non-protective immune responses. In order to confirm the role of Tc13 antigens during T. cruzi infection, herein we studied the humoral and cellular immune responses to the Tc13Tul molecule and its EPKSA C-terminal portion in BALB/c T. cruzi-infected mice or mice immunized with recombinant Tc13Tul. Analysis of the antibody response showed that B-cell epitopes that stimulate a sustained IgM production along the infection and high levels of IgG in the acute phase are mainly located at the Tc13 N- and C-terminal domains, respectively. DTH assays showed that T-cell epitopes are mainly at the Tc13 N-terminal segment and that they do not elicit an efficient memory response. Recombinant Tc13Tul did not induce IFN-γ secretion in either infected or immunized mice. However, a putative CD8+Tc13Tul-derived peptide was found to elicit IFN-γ production in chronically infected animals. Immunization with recombinant Tc13Tul did not induce pathology in tissues and neither did it protect against the infection. Our results show that in the outcome of T. cruzi infection the Tc13 family protein mainly triggers non-protective immune responses.

Mannose-binding lectins were purified from flatfish spotted halibut (Verasper variegatus) serum. These lectins, which we named VVL (Verasper variegatus lectin)-α (~33 kDa) and VVL-β (~30 kDa) (VVLs), under non-reducing SDS-PAGE, were surprisingly highly concentrated in serum (1·92±0·55 mg/ml; n=5), compared with other serum lectins. Both VVLs are heterodimers comprised of 2 types of subunit via inter-subunit disulfide bonds, and one subunit of VVL-α has a N-linked sugar chain. Based on N-terminal amino acid sequences, the nucleotide sequences of one subunit of VVL cDNAs were determined by 3′- and 5′-rapid amplification of the cDNA ends. The full-length VVL subunit cDNAs contained 489 bp, encoding an open reading frame of 163 amino acids. We found that VVLs bind to an ~8 kDa ciliary surface glycoprotein (a putative agglutination/immobilization antigen that we reported previously) of the fish parasite Neobenedenia girellae, and agglutinate this parasite in vitro.

Myxobolus cerebralis, the myxozoan parasite responsible for whirling disease in salmonid fishes, has a complex life-cycle involving an invertebrate host and 2 spore stages. Water flow rate is an environmental variable thought to affect the establishment and propagation of M. cerebralis; however, experimental data that separates flow effects from those of other variables are scarce. To compare how this parameter affected parasite infection dynamics and the invertebrate and vertebrate hosts, dead, infected fish were introduced into a naïve habitat with susceptible hosts under 2 experimental flow regimes: slow (0·02 cm/s) and fast (2·0 cm/s). Throughout the 1-year study, uninfected fry were held in both systems, the outflows were screened weekly for spores and the annelid populations were monitored. We found clear differences in prevalence of infection in the worms, prevalence and severity of infection in the fish, and host survival. Both flows provided environments in which M. cerebralis could complete its life-cycle; however, both the parasite and its invertebrate host proliferated to a greater extent in the slow flow environment over the 1-year study period. This finding is of significance for aquatic systems where the flow rate can be manipulated, and should be incorporated into risk analysis assessments.

Researchers are becoming interested in testing whether investment in growth and/or development trades off against investment in parasite defence. We tested this idea by examining relations between development of Wood Frogs (Rana sylvatica) and susceptibility to lung nematodes (Rhabdias ranae). Male and female frogs reared in outdoor mesocosms were the same length and mass at metamorphosis. However, males metamorphosed sooner than females. Lung nematodes were no more likely to penetrate male versus female metamorphs following controlled exposures, but males had higher intensities of adult female worms and the largest worms per host were, on average, of larger size in male metamorphs. Males that took longer to metamorphose carried higher numbers of worms in their lungs than males that metamorphosed early. In comparison, females that developed faster harboured more worms in their lungs than females that took longer to reach metamorphosis. Our results suggest that variation in susceptibility to lung nematodes is influenced by host sex and possibly also by sex-specific relations with developmental rate. Further, male hosts might prove to be a more important source of infective stages of worms than female hosts.

The aim of this study was to investigate the intra-litter infection dynamics of Isospora suis under natural conditions, and to study any association between parasite transmission and the contamination level of the farrowing pen by applying different interventions in order to reduce the transmission of I. suis infection within the litter. The study was divided in 2 trials including in total 22 litters (254 piglets). The first trial included 4 litters (where standard procedures practiced routinely on the farm piglets were applied) and the piglets were followed coprologically from farrowing until 2 weeks after weaning. The sows of those litters were also examined at various intervals before and after farrowing. The second trial included the application of 3 different management procedures: (A) standard farm hygiene and management procedures, (B) standard farm hygiene and management procedures+the first piglets found to excrete I. suis oocysts in each pen were removed from the pen, and (C) reduced cleaning. Each procedure was studied in 2 litters. This was replicated 3 times to yield a total of 18 litters. The results suggested that (i) the sow does not play an important role in transmission of I. suis in the farrowing pen; (ii) in natural infections, both the age of the piglet age at onset of oocyst excretion and the oocyst excretion patterns may vary considerably; (iii) the course of oocyst excretion or development of diarrhoea is related to the time of initial infection and (iii) piglets, which are heavy at birth, are more prone to acquire I. suis infection. Moreover, it was demonstrated that cleaning could be an effective means of restricting the spread of the parasite within the litter and thus the development of diarrhoea.