The study of host-parasite interactions has increased considerably in the last decades, with many studies focusing on the identification of parasite molecules (i.e. surface or excretory/secretory proteins (ESP)) as potential targets for new specific treatments and/or diagnostic tools. In parallel, in the last few years there have been significant advances in the field of extracellular vesicles research. Among these vesicles, exosomes of endocytic origin, with a characteristic size ranging from 30–100 nm, carry several atypical secreted proteins in different organisms, including parasitic protozoa. Here, we present experimental evidence for the existence of exosome-like vesicles in parasitic helminths, specifically the trematodes Echinostoma caproni and Fasciola hepatica. These microvesicles are actively released by the parasites and are taken up by host cells. Trematode extracellular vesicles contain most of the proteins previously identified as components of ESP, as confirmed by proteomic, immunogold labeling and electron microscopy studies. In addition to parasitic proteins, we also identify host proteins in these structures. The existence of extracellular vesicles explains the secretion of atypical proteins in trematodes, and the demonstration of their uptake by host cells suggests an important role for these structures in host-parasite communication, as described for other infectious agents.

Coprologic surveys were carried out in villages of the Behera Governorate in the Nile Delta region of Egypt to characterize the epidemiologic features of human fascioliasis caused by Fasciola hepatica and F. gigantica in this lowland endemic area by comparison with fascioliasis caused by only F. hepatica in areas hyperendemic for human disease in the Andean highlands of South America. The fascioliasis prevalences detected (range ‫ס‬ 5.2−19.0%, mean ‫ס‬ 12.8%) are the highest obtained in Egypt. The comparison with previous results suggests that in the Nile Delta, fascioliasis is spreading from an original situation of sporadic human cases in well-known endemic foci for animal disease to an endemic distribution in humans, which may be characterized as a mesoendemic region that includes several hyperendemic areas for human disease. As in Andean countries, a relationship with sex was found, although in Egypt prevalences, but not intensities, appeared to be significantly higher in females. All ages appear to be susceptible to liver fluke infection, with prevalences and intensities being lower before and after school age, a situation that is consistent with that detected in Andean countries, although the peak in the 9−11-year-old age group appears less pronounced in Egypt. The intensities were very high when compared with those found in subjects sporadically infected in areas endemic for animal disease, but relatively low for a hyperendemic situation, although the intensities may not be conclusive because of the transmission seasonality of fascioliasis in the Nile Delta. The marked similarities in the qualitative and quantitative spectrums of protozoans and helminths, multiparasitisms, and associations between liver flukes and other parasitic species suggest physiographic-hydrographic and behavioral-social characteristics similar in all areas hyperendemic for human fascioliasis, which are independent of other factors such as climate, altitude, and cultural or religious features. The significant positive association between liver fluke infection and schistosomiasis mansoni detected in one locality has never been described elsewhere, and must be considered relevant from clinical, pathologic, diagnostic, and therapeutic points of view. Interestingly, the relationships of schistosomiasis prevalences and intensities with sex and age follow patterns similar to those found in fascioliasis.

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In the present article, several parasitological features of mice, each experimentally infected with 75 metacercariae of Echinostoma caproni (Trematoda: Echinostomatidae), were studied during the first 12 wk postinfection. Moreover, the early pathological responses also were analyzed and compared with data previously published on other host species of E. caproni to gain further insight into the factors determining worm rejection or establishment of chronic infections. The results obtained show that the pattern of E. caproni infection in mice is consistent with a highly compatible host-parasite system. This combination is characterized by a high worm establishment, high egg output, and long survival of the worms. However, some differences with respect to other highly compatible hosts have been observed, particularly in relation to the survival of the adult worms. Histological studies suggest that the kinetics of goblet cells, mucosal neutrophils, and mononuclear inflammatory cells in the mesentery seem to be essential in determining the course of E. caproni infection in mice.

BackgroundIntestinal protozoan parasites are major contributors to the global burden of gastrointestinal disease causing significant socioeconomic consequences. Children living in resource-poor settings with restricted access to water and sanitary services are particularly at risk of these infections.MethodsA prospective, community-based, cross-sectional survey was conducted in Paraná (southern Brazil) between May 2015 and May 2016. A total of 766 stool samples were individually collected from volunteers (male/female ratio: 0.99; age range: 0–76 years) and used for investigating the presence of intestinal helminth and protozoan species by routine microscopic procedures including the Kato-Katz and modified Ritchie concentration methods and the Ziehl-Neelsen stain technique. Quantitative real-time PCR confirmed microscopy-positive samples for Giardia duodenalis and the assemblages and sub-assemblages determined by multilocus sequence-based genotyping of the glutamate dehydrogenase (gdh) and β-giardin (bg) genes of the parasite. Identification of Blastocystis subtypes was carried out by amplification and sequencing of a partial fragment of the small-subunit ribosomal RNA gene (SSU rDNA) of this heterokont microorganism.ResultsOverall, 46.1% (353/766) of the participants were infected/colonised by at least one intestinal parasite/commensal species. Protozoan and helminth species were detected in 42.7% and 10.1% of the surveyed population, respectively. Blastocystis sp. (28.2%), Endolimax nana (14.9%), and Giardia duodenalis (11.0%) were the most prevalent species found among protozoans and Ascaris lumbricoides (5.0%), Trichuris trichiura (4.6%) and hookworms (1.0%) among helminths. A total of 38 G. duodenalis-positive samples were genotyped at gdh and bg markers, revealing the presence of the sub-assemblages AII (47.4%), AII/AIII (2.6%), BIII (5.3%), BIV (26.3%) and BIII/BIV (13.1%). Two samples (5.3%) were only identified as assemblage B. AII was predominantly found in females aged 5–9 years and was associated with a higher likelihood of reporting gastrointestinal symptoms. A total of 102 Blastocystis-positive samples were successfully subtyped at the SSU rRNA gene revealing the presence of ST1 (36.3%), ST2 (15.7%), ST3 (41.2%), ST4 (2.9%), ST6 (1.0%) and ST8 (2.9%).ConclusionsData presented here indicate that enteric parasites still represent a pressing health concern in Paraná, Brazil, probably due to sub-optimal water, sanitation and hygiene conditions. A mostly anthroponotic origin is suspected for G. duodenalis and Blastocystis sp. infections.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3054-7) contains supplementary material, which is available to authorized users.

The aim of the present study was to compare the development of Echinostoma caproni (Trematoda: Echinostomatidae) adults in two host species displaying different degrees of compatibility with this parasite. For this purpose, the variability in the worm recovery, egg output, and morphology of E. caproni adults during the course of experimental infections in hamsters and rats was analyzed. Student's t-tests and two-factor ANOVA analysis with the time post-infection and the host species as independent variables, and Bonferroni t-tests as post hoc analysis were used for the study. Worm recovery and egg output were host species dependent. The values were significantly higher in the worms established in hamsters than those in rats. The oral sucker area, pre-pharynx length, and pharynx area were the most conservative features, and no significant variability related to the host species was detected. In contrast, body area, collar width, esophagus length, cirrus sac area, ventral sucker area, ovarian area and anterior and posterior testicular areas were significantly higher in those worms collected from hamsters. Moreover, significant worm age-host species interactions were found for body area, ovarian area, ventral sucker area, and anterior and posterior testicular areas.

Echinostoma caproni is an intestinal trematode that has been extensively used as an experimental model to investigate the factors determining the resistance to intestinal helminths or the development of chronic infections. ICR mice are permissive hosts for E. caproni in which chronic infections are developed, concomitantly with local Th1 responses, elevated levels of local IFN-γ, inflammation and antibody responses. However, mice develop partial resistance to homologous challenge infections after cure of a primary infection, which converts this subject into an adequate model for the study of the mechanisms generating resistance against intestinal helminths. The purpose of the present study was to compare the immune response induced in primary and secondary infections to elucidate the factors determining the different outcome of the infection in each type of infection. The results obtained indicate that susceptibility is determined by the lack of IL-25 expression in response to primary infection. In contrast, infection in an environment with elevated levels of IL-25, as occurs in challenge infection, results in a Th2 phenotype impairing parasite survival. This was confirmed by treatment of naïve mice with exogenous IL-25 and subsequent infection. Changes induced in goblet cell populations and mucin glycosylation could be implicated in resistance to infection.