The global epidemiology of clonorchiasis and its relation with cholangiocarcinoma

Please see Additional file 1 for translations of the abstract into the six official working languages of the United Nations.Liver flukes are a polyphyletic group of trematodes (phylum Platyhelminthes), including Clonorchis sinensis, Opisthorchis viverrini and Opisthorchis felineus from family opisthorchiidae and Fasciola spp. from family fasciolidae [1-4]. Here, opisthorchiidae, especially C. sinensis is focused on, so liver flukes are specially termed to this family. Adults of liver flukes, localizing in the liver of various mammals including humans, produce eggs which are passed into the intestine. Most of the parasites live in bile ducts, gallbladder and liver parenchyma, causing liver and biliary diseases. Human beings are infected through ingestion of raw or undercooked fish which contains the metacercariae of liver flukes (Figure 1) [1-4].Cholangiocarcinoma (CCA) is a cancer of the bile ducts. Recent evidences support the fact that CCA is the most severe complication of liver fluke infection, and C. sinensis and O. viverrini infections are both classified as “carcinogenic to humans” (Group 1) by the International Agency for Research on Cancer (IARC) in 2009 [5,6].Due to the absence of definite information on geographical distribution and disease burden, their public health impact has been underestimated for a long time [7]. Here we review the global epidemiological status and characteristics of clonorchiasis and the etiological relationship between C. sinensis infection and CCA.Clonorchiasis is predominantly endemic in east Asia, but it may also occur in other regions where there are immigrants from endemic areas [8]. Due to the growth and movement of population and the rapid development of aquaculture, the fact of clonorchiasis hindering the local economic development is increasingly notified [2,7].Three large-scale surveys for clonorchiasis have been carried out in mainland of China. The prevalence of clonorchiasis was 0.37% according to the first national p