Clonorchiasis

Clonorchiasis is a parasitic disease caused by Clonorchis sinensis, a hepatic trematode whose adult worms reside in the bile ducts of infected humans and other mammalian hosts ^[1]. It belongs to the family Opisthorchiidae, alongside the related liver flukes Opisthorchis viverrini and Opisthorchis felineus, which collectively are regarded as the three most important human liver fluke species ^[3]. The parasite has a complex life cycle involving humans, animal reservoirs, and two kinds of intermediate hosts ^[1].

Clonorchis sinensis infection is primarily related to liver and biliary disorders, with chronic infections associated with hepatobiliary complications, most importantly cholangiocarcinoma ^[1][4]. The disease's clinical spectrum ranges from asymptomatic or mild presentations in light infections to significant hepatobiliary pathology in longstanding, heavy infections, reflecting the parasite's tissue tropism for the biliary tree ^[1][4]. Diagnosis in epidemiologic surveys and for individual patients is most commonly achieved through stool microscopy, while immunologic techniques are employed for screening purposes and molecular techniques facilitate species differentiation in reference laboratories ^[1][4].

Clonorchis sinensis, Opisthorchis viverrini, and Opisthorchis felineus are important liver flukes that cause a considerable public health burden in eastern Asia, southeastern Asia, and eastern Europe, respectively ^[1]. Clonorchiasis mainly occurs in east Asia, as a result of the region's social-ecological systems and deeply rooted cultural habit of consuming raw freshwater fish ^[4]. The life cycles of these liver flukes are complex, involving humans, animal reservoirs, and two kinds of intermediate hosts, and an interplay of biological, cultural, ecological, economic, and social factors drives transmission ^[1]. With regard to diagnosis, stool microscopy is widely used in epidemiologic surveys and for individual diagnosis, while immunologic techniques are employed for screening purposes, and molecular techniques facilitate species differentiation in reference laboratories ^[1]. Pressing research needs include mapping the current distribution, disentangling the transmission, accurately estimating the disease burden, and developing new diagnostic and treatment tools, which would aid to optimize control and elimination measures, since the precise distribution, the exact number of infected people, subtle morbidities and pathogenesis, and the global burden of clonorchiasis remain unknown ^[1][4]. The epidemiology of clonorchiasis encompasses global and regional risk factors for the infection and its transmission, requiring comprehensive studies to devise effective methods for diagnosis, treatment, and prevention of this zoonosis .

Transmission of Clonorchis sinensis to humans occurs through the consumption of raw or undercooked freshwater fish containing the infective metacercariae, a practice deeply embedded in certain cultural traditions in endemic regions ^[2]. The parasite's life cycle involves humans, animal reservoirs, and two kinds of intermediate hosts, with an interplay of biological, cultural, ecological, economic, and social factors driving ongoing transmission ^[1][2]. Animal reservoirs serve to maintain the parasite in the environment, and drug treatment that lowers worm burdens can contribute to reducing community-level transmission in addition to controlling individual morbidity ^[3].

The mainstay of clonorchiasis control is preventive chemotherapy with praziquantel, which serves as the treatment of choice and has been considered for population-level deworming in endemic areas ^[1][4]. This pharmacological approach is typically combined with information, education, and communication activities aimed at promoting behavioral change, particularly discouraging the consumption of raw freshwater fish, as well as environmental management strategies ^[1][4]. Integrated control strategies incorporating preventive chemotherapy, health education, environmental management, and capacity building through intersectoral collaboration are advocated ^[4]. Tribendimidine, registered in the People's Republic of China for soil-transmitted helminth infections, has shown potential against C. sinensis in phase 2 trials and warrants further clinical development as an additional control tool ^[1][4]. Novel approaches under investigation include fish vaccines and biological control methods ^[1].

1. 1Qian M-B et al. Clonorchiasis and opisthorchiasis: epidemiology, transmission, clinical features, morbidity, diagnosis, treatment, and control. Clin Microbiol Rev. 2024 Mar 14. PMID: 38169283. doi: 10.1128/cmr.00009-23.PubMed: https://pubmed.ncbi.nlm.nih.gov/38169283/
2. 2Chelomina GN et al. [(CLONORCHIASIS: GLOBAL AND REGIONAL EPIDEMIOLOGY)]. Med Parazitol (Mosk). 2017 Apr. PMID: 30721606.PubMed: https://pubmed.ncbi.nlm.nih.gov/30721606/
3. 3Qian MB et al. Efficacy of drugs against clonorchiasis and opisthorchiasis: a systematic review and network meta-analysis. Lancet Microbe. 2022 Aug. PMID: 35697047. doi: 10.1016/S2666-5247(22)00026-X.PubMed: https://pubmed.ncbi.nlm.nih.gov/35697047/
4. 4Qian MB et al. Clonorchiasis. Lancet. 2016 Feb 20. PMID: 26299184. doi: 10.1016/S0140-6736(15)60313-0.PubMed: https://pubmed.ncbi.nlm.nih.gov/26299184/