Foodborne zoonotic trematode (FZT) infections are common neglected tropical diseases in Southeast Asia. Their complicated life cycles involve freshwater snails as intermediate hosts. A cross-sectional study was conducted in Yen Bai and Thanh Hoa provinces in North and Central Vietnam, to investigate the diversity of cercariae of potential FZT and to construct the phylogenetic relationship of trematode cercariae based on the Internal Transcribed Spacer 2 (ITS2) region. Among 17 snail species collected from various habitats, 13 were infected by 10 cercarial groups among which parapleurolophocercous, pleurolophocercous, and echinostome cercariae were of zoonotic importance. The monophyletic tree separated cercarial sequences into different groups following the description of the cercariae families in which Haplorchidae, Opisthorchiidae, Echinochasmidae, and Echinostomatidae are important families of FZT. The overall prevalence was different among snail species and habitats and showed a seasonal trend. Parapleurolophocercous and echinostome cercariae emerged as the most common cercariae in snails in Yen Bai, while monostome, echinostome, and megalura cercariae were most common in Thanh Hoa. Using a molecular approach, we identified Parafossarulus striatulus as the first intermediate snail host of Clonorchis sinensis in Thac Ba Lake. Melanoides tuberculata and Bithynia fuchsiana were we identified preferred intermediate snail hosts of a diverse range of trematode species including intestinal flukes (i.e., Haplorchis pumilio and Echinochasmus japonicus) in Yen Bai and Thanh Hoa, respectively.

Sulfated exopolysaccharides have been well-known to enhance biological activities. Exopolysaccharide (EPS) produced by Ophiocordyceps sinensis fungus is a source of natural compounds. The aim of our study is to improve the EPS biological activities by its sulfated modification using the chlorosulfonic acid (CSA)-pyridine (Pyr) method. The appropriate conditions of the sulfation reaction were explored, including CSA/Pyr ratio (v/v) of 1:3 and 6h. The degree of substitution (DS) of S-EPS11 was the highest (DS = 1.59). The total contents of polysaccharides and SO42- of S-EPS11 were 52.25% and 47.15%, respectively. Besides, the FT-IR spectra analysis indicated the presence of CO-S (peak of 815 cm-1) and S=O (peak of 1129 cm-1) stretching vibrations, while the natural EPS did not appear. Importantly, OH• and ABTS• radical scavenging potential of S-EPS11 significantly increased compared with those of the natural EPS. Together, we successfully generated sulfated EPS extracted from O. sinensis fungus which enhanced antioxidant activities of natural EPS.