More than 750 million people are at risk of infection with foodborne liver flukes. Opisthorchis viverrini is considered among the most important of these parasites, due to its strong association with cholangiocarcinoma (CCA). O. viverrini infection results in a chronic inflammatory challenge to the host, which can lead to advanced, pathogen-specific disease sequelae including obstructive jaundice, hepatomegaly, cholecystitis, as well as CCA. However, before disease sequelae are apparent, important inflammatory changes to the liver can be detected early during O. viverrini infection. In a case-control study involving 328 men and women with O. viverrini infection, we determined the presence of advanced periductal fibrosis in asymptomatic, O. viverrini-infected individuals and then measured cytokine responses to O. viverrini excretory/secretory products (ES). In the 200 participants with advanced periductal fibrosis (cases), levels of interleukin-6 (IL-6) to O. viverrini ES were 8 times higher than levels of the 128 O. viverrini-infected individuals without advanced periductal fibrosis (controls). Moreover, elevated IL-6 to parasite ES was associated with increased risk of advanced periductal fibrosis by 63% in a model adjusted for sex and age. The risk of advanced periductal fibrosis was also found to increase with higher levels of IL-6: individuals in the third quartile of IL-6-ES production had a 127% higher risk of developing advanced periductal fibrosis than individuals in the first quartile of IL-6 production. O. viverrini-infected individuals with advanced periductal fibrosis showed other hepatobiliary abnormalities, including reduced gallbladder contractility and the presence of gallbladder sludge.
Conclusion: These data strongly implicate a role for parasite-specific IL-6 in the pathogenesis of advanced periductal fibrosis in opisthorchiasis, with possible links to other hepatobiliary abnormalities, including CCA.