Fasciola hepatica surface tegument: glycoproteins at the interface of parasite and host

Fasciola hepatica, commonly known as liver fluke, is a trematode which causes Fasciolosis in ruminants and humans. The outer tegumental coat of F. hepatica (FhTeg) is a complex metabolically active biological matrix that is continually exposed to the host immune system and therefore makes a good vaccine target. F. hepatica tegumental coat is highly glycosylated and helminth-derived immunogenic oligosaccharide motifs and glycoproteins are currently being investigated as novel vaccine candidates. This report presents the first systematic characterisation of FhTeg glycosylation using lectin microarrays to characterise carbohydrates motifs present, and lectin histochemistry to localize these on the F. hepatica tegument. We discovered that FhTeg glycoproteins are predominantly oligomannose oligosaccharides that are expressed on the spines, suckers and tegumental coat of F. hepatica and lectin blot analysis confirmed the abundance of N- glycosylated proteins. While some oligosaccharides are widely distributed on the fluke surface other subsets are restricted to distinct anatomical regions. We selectively enriched for FhTeg mannosylated glycoprotein subsets using lectin affinity chromatography and identified 369 proteins by mass spectrometric analysis. Among these proteins are a number of potential vaccine candidates with known immune modulatory properties including proteases, protease inhibitors, paramyosin, Venom Allergen-like II, Enolase and two proteins, nardilysin and TRIL, that have not been previously associated with F. hepatica Furthermore, we provide a comprehensive insight regarding the putative glycosylation of FhTeg components which could highlight the importance of further studies examining glycoconjugates in host-parasite interactions in the context of F. hepatica infection and the development of an effective vaccine.

Wolbachia infections of tephritid fruit flies: molecular evidence for five distinct strains in a single host species

Endosymbiotic bacteria of the genus Wolbachia are widespread among arthropods and can induce cytoplasmic incompatibility, thelytokous parthenogenesis, male-killing or feminization in their hosts. Here, we report phylogenetic relationships of Wolbachia in tephritid fruit flies based on wsp gene sequences. We also report, for the first time, five distinct strains of Wolbachia in Bactrocera ascita sp. B. Four of the five Wolbachia strains found in this species were in the same groups as those found in other tephritid fruit flies, suggesting possible horizontal transmission of Wolbachia from other fruit flies into B. ascita sp. B. The unreliability of wsp-specific group primers demonstrated in this study suggests that these primers might be useful only for preliminary identification of Wolbachia. Final determination of group affiliation needs to be verified with wsp sequence data.

Ultrastructure and small-subunit ribosomal DNA sequence of Henneguya lesteri n. sp (Myxosporea), a parasite of sand whiting Sillago analis (Sillaginidae) from the coast of Queensland, Australia

Henneguya lesteri n. sp, (Myxosporea) is described from sand whiting, Sillago analis, from the southern Queensland coast of Australia. H. lesteri displays a preference for the pseudobranchs and is typically positioned along the afferent blood vessels, displacing the adjoining lamellae and disrupting their normal array, The plasmodia appeared as whitish-hyaline, elliptical cysts (mean dimensions 230 x 410 mum) attached to the oral mucosa lining of the hyoid arch on the inner surface of the operculum. Infections of the gills were also found, in which the plasmodia were spherical, averaged 240 x 240 mum in size and were located on the inner hemibranch margin. The parasites lodged in the gill filament crypts and generated a mild hyperplastic response of the branchial epithelium, In histological sections, the plasmodium wall and adjoining ectoplasm appeared as a finely granulated, weakly eosinophilic layer, Ultrastructurally, this section of the host-parasite interface contained an intricate complex of pinocytotic channels. H. lesteri is polysporic, disporoblastic and pansporoblast forming. Sporogenesis is asynchronous, with the earliest developmental stages aligned predominantly along the plasmodium periphery, and maturing sporoblasts and spores toward the center. Ultrastructural details of sporoblast and spore development are in agreement with previously described myxosporeans. The mature spore is drop-shaped, length (mean) 9.1 mum, width 4.7 mum, thickness 2.5 mum, and comprises 2 polar capsules positioned closely together, a binucleated sporoplasm and a caudal process of 12.6 mum. The polar capsules are elongated, 3.2 x 1.6 mum, with 4 turns of the polar filament. Mean length of the everted filament is 23.2 mum, Few studies have analyzed the 18S gene-of marine Myxosporea. In fact, H. lesteri is the first marine species of Henneguya to be characterized at the molecular level: we determined 1966 bp of the small-subunit (18S) rDNA, The results indicated that differences between this and the hitherto studied freshwater Henneguya species are greater than differences among the freshwater Henneguya species.

Cleavage of hemoglobin by hookworm cathespin D aspartic proteases and its potential contribution to host specificity

Hookworms routinely reach the gut of nonpermissive hosts but fail to successfully feed, develop, and reproduce. To investigate the effects of host-parasite coevolution on the ability of hookworms to feed in nonpermissive hosts, we cloned and expressed aspartic proteases from canine and human hookworms. We show here that a cathepsin D-like protease from the canine hookworm Ancylosotoma caninum (Ac-APR-1) and the orthologous protease from the human hookworm Necator americanus (Na-APR-1) are expressed in the gut and probably exert their proteolytic activity extracellularly. Both proteases were detected immunologically and enzymatically in somatic extracts of adult worms. The two proteases were expressed in baculovirus, and both cleaved human and dog hemoglobin (Hb) in vitro. Each protease digested Hb from its permissive host between twofold (whole molecule) and sixfold (synthetic peptides) more efficiently than Hb from the nonpermissive host, despite the two proteases' having identical residues lining their active site clefts. Furthermore, both proteases cleaved Hb at numerous distinct sites and showed different substrate preferences. The findings suggest that the paradigm of matching the molecular structure of the food source within a host to the molecular structure of the catabolic proteases of the parasite is an important contributing factor for host-parasite compatibility and host species range.

Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease: 3 - On the interaction of vector species and parasite strain in the reaction of bugs to infection by Trypanosoma cruzi

The reaction of nine vector species of Chagas' disease to infection by seven different Trypanosoma cruzi strains; Berenice, Y, FL, CL, S. Felipe, Colombiana and Gávea, are examined and compared. On the basis of the insects' ability to establish and maintain the infection, vector species could be divided into two distinct groups which differ in their reaction to an acute infection by T. cruzi. While the proportion of positive bugs was found to be low in Triatoma infestans and Triatoma dimidiata it was high, ranging from 96.9% to 100% in the group of wild (Rhodnius neglectus, Triatoma rubrovaria)and essentially sylvatic vectors in process of adaptation to human dwellings, maintained under control following successful insecticidal elimination of Triatoma infestans (Panstrongylus megistus, Triatoma sordida and Triatoma pseudomaculata). An intermediate position is held by Triatoma brasiliensis and Rhodnius prolixus. This latter has been found to interchange between domestic and sylvatic environments. The most important finding is the strikingly good reaction between each species of the sylvatic bugs and practically all T. cruzi strains herein studied, thus indicating that the factors responsible for the excellent reaction of P.megistus to infection by Y strain, as previously reported also come into operation in the reaction of the same vector species to acute infections by five of the remaining T.cruzi strains. Comparison or data reported by other investigators with those herein described form the basis of the discussion of Dipetalogaster maximus as regards its superiority as a xenodiagnostic agent.

Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease: 4 - The reflection of parasite stock in the responsiveness of different vector species to chronic infection with different Trypanosoma cruzi stocks

Previous studies (1982,1987) have emphasized the superiority of sylvatic vector species over domestic species as xenodiagnostic agents in testing hosts with acute or chronic infections by T. cruzi "Y" stock. The present study, which is unique in that it contains data on both infectivity rates produced by the same stock in 11 different vector species and also the reaction of the same vector species to seven different parasite stocks, establishes the general validity of linking efficiency of xenodiagnosis to the biotope of its agent. For example, infectivity rates produced by "São Felipe" stock varied from 82.5% to 98.3% in sylvatic vectors but decreased to 42.5% to 71.3% in domestic species. "Colombiana" stock produced in the same sylvatic vectors infectivity rates ranging from 12.5% to 45%. These shrank to 5%-22.5% in domestic bugs. The functional role of the biotope in the vector-parasite interaction has not been eluddated. But since this phenomenon has been observed to be stable and easy to reproduce, it leads us to believe that the results obtained are valid. Data presented also provide increasing evidence that the infectivity rates exhibited by bugs from xenodiagnosis in chronic hosts, are parasite stock specific. For example, infectivity rates produced by "Berenice", "Y", "FL" and "CL" varied in R. neglectus from 26.3% to 75%; in P. megistus from 56.3% to 83.8%; in T. sordida from 28.8% to 58.8% in T. pseudomaculata from 41.3% to 66.3% and in T. rubrovaria from 48.8% to 85%. Data from xenodiagnosis in the same hosts, carrying acute infections by the same parasite stocks, gave the five sylvatic vectors a positive rating of approximately 100%, thus suggesting that the heavy loads of parasites circulating in the acute hosts obscured the characteristic interspecific differences for the parasite stock. Nonetheless these latter were revealed in the same hosts with chronic infections stimulated by very low numbers of the same parasite stocks. Certain observations here described lead us to speculate as to the possibility of further results from other parasite stocks, allowing the association of the infectivity rates produced in bugs by different parasite stocks with the isoenzymic patterns revealed by these stocks.

Evaluation of the resistance to Schistosoma mansoni infection in Nectomys squamipes (Rodentia: Cricetidae), a natural host of infection in Brazil

The development of resistance in three stages throughout an active infection (pre-ovular, acute and initial chronic stages) was studied, comparing the total number of adult worms recovered from the reinfected group and the control groups. It was shown that Nectomys squamipes was unable to develop resistance in the tested conditions and, on the other hand, reinfection in the pre-ovular period of the parasite led the rodent to present the phenomenonacilitation, with reduction of natural resistance and an increase in the parasite load. These results suggest the existence of other forms of immunity diverse from the concomitant immunity in the host-parasite relationship, according to the employed model.

Helminths of introduced house sparrows (Passer domesticus) in Brazil: does population age affect parasite richness?

Species introductions have altered host and parasite diversity throughout the world. In the case of introduced hosts, population age appears to be a good predictor of parasite richness. Habitat alteration is another variable that may impact host-parasite interactions by affecting the availability of intermediate hosts. The house sparrow (Passer domesticus (Linnaeus, 1758)) is a good model to test these predictions. It was introduced in several parts of the world and can be found across rural-urban gradients. A total of 160 house sparrows from Porto Alegre, state of Rio Grande do Sul, Brazil, were necropsied. Thirty house sparrows (19 %) were parasitized with at least one out of five helminth species (Digenea: Tamerlania inopina Freitas, 1951 and Eumegacetes sp.; Eucestoda: Choanotaenia passerina (Fuhrmann, 1907) Fuhrmann, 1932; Nematoda: Dispharynx nasuta (Rudolphi, 1819) Stiles & Hassall, 1920 and Cardiofilaria pavlovskyi Strom, 1937). Overall, there was no difference in prevalence and intensity of infection of any parasite species, parasite richness and community diversity between adult males and females and adults and juveniles. The number of infected sparrows among seasons, the richness of helminths and the abundance of species were also similar between rural and urban landscapes. Only the prevalence of C. passerina varied seasonally (p=0.0007). A decrease in the number of parasite species from the original range of P. domesticus (13) to its port of entrance in Brazil, the city of Rio de Janeiro (nine), to Porto Alegre (five) is compatible with the hypothesis that host population age is a good predictor of parasite richness.

Eurytrema coelomaticum (Digenea, Dicrocoeliidae): the effect of infection on carbohydrate contents of its intermediate snail host, Bradybaena similaris (Gastropoda, Xanthonychidae)

The interface Eurytrema coelomaticum/Bradybaena similaris was studied by quantifying the amount of glucose on the hemolymph and the content of glycogen in the cells of the digestive gland and the cephalopedal mass of infected and uninfected snails. Samples were analyzed on days 0, 30, 90 and 150 post-infection. The infected snails had less glucose in the hemolymph, with a reduction of 67.05 por cento at 30 days, and 62.09 por cento at 90 days post-infection. The reduction in glycogen content was 86.41 por cento in the digestive gland and 79.1 por cento in the cephalopedal mass at 30 days, and 92.71 por cento and 90.89 por cento in these organs respectively at 90 days post-infection. It is proposed that the sporocysts absorb glucose directly from the hemolymph.

Host-ectoparasite specificity in a small mammal community in an area of Atlantic Rain Forest (Ilha Grande, State of Rio de Janeiro), Southeastern Brazil

The analyses of the ectoparasite species associated with a small mammal community on Ilha Grande, a coastal island in southern of the state of Rio de Janeiro, Brazil, evaluated the level of host-ectoparasite specificity. Was used the Jaccard index for qualitative data to analyse the similarity. The lowest value of similarity occurred between Proechimys iheringi and Marmosops incanus and between Sciurus aestuans and Nectomys squamipes (Cj = 0.08) and the highest between P. iheringi and Oxymycterus sp. (Cj = 0.33). This index showed a low value of similarity across the ectoparasite community. The only exception from this pattern of high host specificity occurred with P. iheringi and Oxymycterus sp., which shared five species of ectoparasites. The similarity values, for most of the cases, is smaller than 0.2.

The spread of incompatibility-inducing parasites in sub-divided host populations.

BACKGROUND:Maternally transmitted symbionts have evolved a variety of ways to promote their spread through host populations. One strategy is to hamper the reproduction of uninfected females by a mechanism called cytoplasmic incompatibility (CI). CI occurs in crosses between infected males and uninfected females and leads to partial to near-complete infertility. CI-infections are under positive frequency-dependent selection and require genetic drift to overcome the range of low frequencies where they are counter-selected. Given the importance of drift, population sub-division would be expected to facilitate the spread of CI. Nevertheless, a previous model concluded that variance in infection between competing groups of breeding individuals impedes the spread of CI.RESULTS:In this paper we derive a model on the spread of CI-infections in populations composed of demes linked by restricted migration. Our model shows that population sub-division facilitates the invasion of CI. While host philopatry (low migration) favours the spread of infection, deme size has a non-monotonous effect, with CI-invasion being most likely at intermediate deme size. Individual-based simulations confirm these predictions and show that high levels of local drift speed up invasion but prevent high levels of prevalence across the entire population. Additional simulations with sex-specific migration rates further show that low migration rates of both sexes are required to facilitate the spread of CI.CONCLUSION:Our analyses show that population structure facilitates the invasion of CI-infections. Since some level of sub-division is likely to occur in most natural populations, our results help to explain the high incidence of CI-infections across species of arthropods. Furthermore, our work has important implications for the use of CI-systems in order to genetically modify natural populations of disease vectors.

Potential evidence of parasite avoidance in an avian malarial vector

Epidemiological studies of malaria or other vector-transmitted diseases often consider vectors as passive actors in the complex life cycle of the parasites, assuming that vector populations are homogeneous and vertebrate hosts are equally susceptible to being infected during their lifetime. However, some studies based on both human and rodent malaria systems found that mosquito vectors preferentially selected infected vertebrate hosts. This subject has been scarcely investigated in avian malaria models and even less in wild animals using natural host-parasite associations. We investigated whether the malaria infection status of wild great tits, Parus major, played a role in host selection by the mosquito vector Culex pipiens. Pairs of infected and uninfected birds were tested in a dual-choice olfactometer to assess their attractiveness to the mosquitoes. Plasmodium-infected birds attracted significantly fewer mosquitoes than the uninfected ones, which suggest that avian malaria parasites alter hosts' odours involved in vector orientation. Reaction time of the mosquitoes, that is, the time taken to select a host, and activation of mosquitoes, defined as the proportion of individuals flying towards one of the hosts, were not affected by the bird's infection status. The importance of these behavioural responses for the vector is discussed in light of recent advances in related or similar model systems.

Variation in intensity of a parasitic mite (Spinturnix myoti) in relation to the reproductive cycle and immunocompetence of its bat host (Myotis myotis)

Given the intimate association in host-parasite systems, parasites are expected to initiate their own reproduction when vulnerable hosts become abundant and/or when adult hosts are less resistant. In this study, we examined the variation in the intensities of a blood-sucking mite (Spinturnix myoti, Acarina) with respect to the reproductive cycle and immunocompetence of its host, the greater mouse-eared bat Myotis myotis. Reproductive, pregnant females were less immunocompetent and harboured more parasites than nonreproductive females, whilst, during lactation, immunocompetence was positively associated with female body mass. There was a dramatic increase in the T-cell response of gravid females with the advancement of gestation, which coincided with a diminution of individual parasite loads and a progressive switch of parasites from adults to juveniles. The latter not only harboured greater numbers of mites than adult female bats, but they also exhibited gravid parasites in higher proportions, indicating that juvenile hosts are more attractive for parasite reproduction than adult females.

Causal mechanisms underlying host specificity in bat ectoparasites.

In parasites, host specificity may result either from restricted dispersal capacity or from fixed coevolutionary host-parasite adaptations. Knowledge of those proximal mechanisms leading to particular host specificity is fundamental to understand host-parasite interactions and potential coevolution of parasites and hosts. The relative importance of these two mechanisms was quantified through infection and cross-infection experiments using mites and bats as a model. Monospecific pools of parasitic mites (Spinturnix myoti and S. andegavinus) were subjected either to individual bats belonging to their traditional, native bat host species, or to another substitute host species within the same bat genus (Myotis). The two parasite species reacted differently to these treatments. S. myoti exhibited a clear preference for, and had a higher fitness on, its native host, Myotis myotis. In contrast, S. andegavinus showed no host choice, although its fitness was higher on its native host M. daubentoni. The causal mechanisms mediating host specificity can apparently differ within closely related host-parasite systems.