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The Chinese liver fluke, Clonorchis sinensis, causes the disease clonorchiasis, affecting ~35 million people in regions of China, Vietnam, Korea and the Russian Far East. Chronic clonorchiasis causes cholangitis and can induce a malignant cancer, called cholangiocarcinoma, in the biliary system. Control in endemic regions is challenging, and often relies largely on chemotherapy with one anthelmintic, called praziquantel. Routine treatment carries a significant risk of inducing resistance to this anthelmintic in the fluke, such that the discovery of new interventions is considered important. It is hoped that the use of molecular technologies will assist this endeavour by enabling the identification of drug or vaccine targets involved in crucial biological processes and/or pathways in the parasite. Although draft genomes of C. sinensis have been published, their assemblies are fragmented. In the present study, we tackle this genome fragmentation issue by utilising, in an integrated way, advanced (second- and third-generation) DNA sequencing and informatic approaches to build a high-quality reference genome for C. sinensis, with chromosome-level contiguity and curated gene models. This substantially-enhanced genome provides a resource that could accelerate fundamental and applied molecular investigations of C. sinensis, clonorchiasis and/or cholangiocarcinoma, and assist in the discovery of new interventions against what is a highly significant, but neglected disease-complex., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Clonorchiasis is a neglected tropical disease caused by the Chinese liver fluke, Clonorchis sinensis, and is often associated with a malignant form of bile duct cancer (cholangiocarcinoma). Although some aspects of the epidemiology of clonorchiasis are understood, little is known about the genetics of C. sinensis populations. Here, we conducted a comprehensive genetic exploration of C. sinensis from endemic geographic regions using complete mitochondrial protein gene sets. Genomic DNA samples from C. sinensis individuals (n = 183) collected from cats and dogs in China (provinces of Guangdong, Guangxi, Hunan, Heilongjiang and Jilin) as well as from rats infected with metacercariae from cyprinid fish from the Russian Far East (Primorsky Krai region) were deep sequenced using the BGISEQ-500 platform. Informatic analyses of mitochondrial protein gene data sets revealed marked genetic variation within C. sinensis; significant variation was identified within and among individual worms from distinct geographical locations. No clear affiliation with a particular location or host species was evident, suggesting a high rate of dispersal of the parasite across endemic regions. The present work provides a foundation for future biological, epidemiological and ecological studies using mitochondrial protein gene data sets, which could aid in elucidating associations between particular C. sinensis genotypes/haplotypes and the pathogenesis or severity of clonorchiasis and its complications (including cholangiocarcinoma) in humans., Competing Interests: The authors have declared that no competing interests exist.