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Background: The liver fluke Opisthorchis viverrini infects several million people in Southeast Asia. Adult flukes live in the bile ducts of humans, where they cause hepatobiliary pathology, including cholangiocarcinoma. Here, we investigated the potential of extracellular vesicles (EVs) secreted by the fluke and defined recombinant proteins derived from EVs to generate protective immunity in a hamster vaccination-challenge model. Methodology/Principal findings: EVs isolated from the excretory-secretory products of O. viverrini and two recombinant EV surface proteins encoding the large extracellular loops (LEL) of Ov-TSP-2 (rOv-TSP-2) and Ov-TSP-3 (rOv-TSP-3) were adjuvanted and used to vaccinate hamsters intraperitoneally followed by challenge infection with O. viverrini metacercariae. The number of adult flukes recovered from hamsters immunized with EVs, rOv-TSP-2, rOv-TSP-3 and rOv-TSP-2+rOv-TSP-3 were significantly reduced compared to control animals vaccinated with adjuvant alone. The number of eggs per gram feces was also significantly reduced in hamsters vaccinated with rOv-TSP-2 compared to controls, but no significant differences were found in the other groups. The average length of worms recovered from hamsters vaccinated with EVs, rOv-TSP-2 and rOv-TSP-3 was significantly shorter than that of worms recovered from the control group. Anti-EV IgG levels in serum and bile were significantly higher in hamsters vaccinated with EVs compared to control hamsters both pre- and post-challenge. In addition, levels of anti-rOv-TSP antibodies in the serum and bile were significantly higher than control hamsters both pre- and post-challenge. Finally, antibodies against rOv-TSP-2 and rOv-TSP-3 blocked uptake of EVs by human primary cholangiocyte in vitro, providing a plausible mechanism by which these vaccines exert partial efficacy and reduce the intensity of O. viverrini infection. Conclusion/Significance: Liver fluke EVs and recombinant tetraspanins derived from the EV surface when administered to hamsters induce antibody responses that block EV uptake by target bile duct cells and exert partial efficacy and against O. viverrini challenge. [ABSTRACT FROM AUTHOR]

The article discusses the need for more research on the molecular biology of snails that harbor parasites, specifically focusing on the liver fluke Opisthorchis viverrini. The liver fluke is a leading cause of bile-duct cancer in Southeast Asia. The authors generated the first reference transcriptome of the Bithynia siamensis goniomphalos snail, which is an intermediate host for O. viverrini. The transcriptome provides valuable information for future studies on the biology of the liver fluke and the interactions between the parasite and the snail. The authors hope that this research will contribute to the development of new strategies to control snail-borne diseases. [Extracted from the article]

Background: The human liver fluke, Opisthorchis viverrini, is designated as a group 1 carcinogen, and is the major risk factor for cholangiocarcinoma in endemic countries throughout Southeast Asia. Proteins in the excretory-secretory products and tegumental surface membranes of the fluke have been proposed to play pivotal roles in parasite survival in the host, and subsequent pathogenesis. These macromolecules are therefore valid targets for the development of vaccines and new drugs to control the infection. Tetraspanins (TSP) are prominent components of the tegument of blood flukes where they are essential for tegument formation, are directly exposed to the immune system, and are major targets for a schistosomiasis vaccine. We propose that similar molecules in the surface membranes of O. viverrini are integral to tegument biogenesis and will be efficacious vaccine antigens. Methodology/Principal Findings: The cDNA sequence encoding O. viverrini tetraspanin-1 (Ov-TSP-1) was identified and cloned. The Ov-tsp-1gene was isolated from a cDNA library. Ov-tsp-1 mRNA was expressed most highly in metacercariae and eggs, and to a lesser extent in juvenile and adult worms. Immunolocalization with adult flukes confirmed that Ov-TSP-1 was expressed in the tegument and eggs in utero. Western blot analysis of rOv-TSP-1 probed with sera from O. viverrini-infected humans and hamsters indicated that both hosts raise antibody responses against the native TSP. Using RNA interference we silenced the expression level of Ov-tsp-1 mRNA in adult flukes by up to 72% by 10 days after delivery of dsRNA. Ultrastructural morphology of adult worms treated with Ov-tsp-1 dsRNA displayed a distinctly vacuolated and thinner tegument compared with controls. Conclusions/Significance: This is the first report of a tetraspanin from the tegument of a liver fluke. Our data imply that tetraspanins play important structural roles in the development of the tegument in the adult fluke. Potential uses of O. viverrini tetraspanins as novel interventions are discussed. Author Summary: Liver fluke infection is a fish borne disease that afflicts millions of residents in Thailand and Laos. Infection results from eating undercooked freshwater fish contaminated with larvae of the worm Opisthorchis viverrini. Infection can lead to cancer of the bile ducts (cholangiocarcinoma). Indeed, O. viverrini is designated as a Group 1 carcinogen by the World Health Organization, i.e. a definitive cause for cancer. Proteins produced at the surface and/or released from this parasite play pivotal roles in maintaining the infection and disease. These proteins are valid targets for development of vaccines and new drugs. Tetraspanins are prominent in the tegument (the surface covering) of parasites closely related to O. viverrini where they are exposed to immune responses. Similar molecules on the surface of O. viverrini may be vital for the parasite's survival and may make effective vaccines. Here the gene coding for O. viverrini tetraspanin-1 (Ov-TSP-1) was investigated. We used electron microscopy to show that Ov-TSP-1 is expressed in the tegument. We then silenced expression of the gene encoding Ov-TSP-1 and showed that this resulted in malformation of the tegument, highlighting the importance of this molecule for parasite development and its potential as a vaccine target. [ABSTRACT FROM AUTHOR]

Opisthorchis viverrini is considered among the most important of the food-borne trematodes due to its strong association with advanced periductal fibrosis and bile duct cancer (cholangiocarcinoma). We investigated the relationship between plasma levels of Interleukin (IL)-6 and the risk of developing advanced fibrosis and bile duct cancer from chronic Opisthorchis infection. We show that IL-6 circulates in plasma at concentrations 58 times higher in individuals with advanced fibrosis than age, sex, and nearest-neighbor matched controls and 221 times higher in individuals with bile duct cancer than controls. We also observed a dose-response relationship between increasing levels of plasma IL-6 and increasing risk of advanced fibrosis and bile duct cancer; for example, in age and sex adjusted analyses, individuals with the highest quartiles of plasma IL-6 had a 19 times greater risk of developing advanced periductal fibrosis and a 150 times greater risk of developing of bile duct cancer than individuals with no detectable level of plasma IL-6. Finally, we show that a single plasma IL-6 measurement has excellent positive predictive value for the detection of both advanced bile duct fibrosis and bile duct cancer in regions with high O. viverrini transmission. These data support our hypothesis that common mechanisms drive bile duct fibrosis and bile duct tumorogenesis from chronic O. viverrini infection. Our study also adds a unique aspect to the literature on circulating levels of IL-6 as an immune marker of hepatobiliary pathology by showing that high levels of circulating IL-6 in plasma are not related to infection with O. viverrini, but to the development of the advanced and often lethal pathologies resulting from chronic O. viverrini infection. Author Summary: O. viverrini is among the few parasites considered a Class 1 carcinogen because of its strong association with bile duct cancer (cholangiocarcinoma). Currently, more than 40 million people are infected with O. viverrini worldwide. Thailand has the highest prevalence of O. viverrini at 10 million people infected and also the highest incidence of Opisthorchis-associated bile duct cancer (cholangiocarcinoma) in the world. In the current study, we also show that levels of IL-6 in plasma are associated in a dose-dependent fashion with Opisthorchis-induced bile duct fibrosis (periductal fibrosis) and cholangiocarcinoma. More importantly, we show that O. viverrini infection alone does not elevate IL-6 levels in the plasma. It is only in the presence of these advanced pathologies (advanced fibrosis or cholangiocarcinoma) from chronic O. viverrini infection that significantly elevates plasma levels of IL-6 are observed. Moreover, we show that plasma IL-6 is an easily accessible biomarker for the detection of advanced periductal fibrosis and cholangiocarcinoma, which would be a critical advance for this region of Thailand and other countries in Southeast Asia, where the prevalence of O. viverrini infection can reach as high as 80% and the incidence of bile duct cancer is the highest in the world. [ABSTRACT FROM AUTHOR]