Paiboon Sithithaworn

Liver Fluke Induces Cholangiocarcinoma

The authors discuss the molecular pathogenesis of opisthorchiasis and associated cholangiocarcinogenesis, particularly nitrative and oxidative DNA damage and the clinical manifestations of cholangiocarcinoma.

Exome sequencing identifies distinct mutational patterns in liver fluke–related and non-infection-related bile duct cancers

The impact of different carcinogenic exposures on the specific patterns of somatic mutation in human tumors remains unclear. To address this issue, we profiled 209 cholangiocarcinomas (CCAs) from Asia and Europe, including 108 cases caused by infection with the liver fluke Opisthorchis viverrini and 101 cases caused by non–O. viverrini–related etiologies. Whole-exome sequencing (n = 15) and prevalence screening (n = 194) identified recurrent somatic mutations in BAP1 and ARID1A, neither of which, to our knowledge, has previously been reported to be mutated in CCA. Comparisons between intrahepatic O. viverrini–related and non–O. viverrini–related CCAs demonstrated statistically significant differences in mutation patterns: BAP1, IDH1 and IDH2 were more frequently mutated in non–O. viverrini CCAs, whereas TP53 mutations showed the reciprocal pattern. Functional studies demonstrated tumor suppressive functions for BAP1 and ARID1A, establishing the role of chromatin modulators in CCA pathogenesis. These findings indicate that different causative etiologies may induce distinct somatic alterations, even within the same tumor type.

Opisthorchiasis and Opisthorchis-associated cholangiocarcinoma in Thailand and Laos

Liver fluke infection caused by Opisthorchis viverrini is a major public health problem in Thailand and the Lao Peoples Democratic Republic (Lao PDR; Laos). Currently, more than 600 million people are at risk of infection with these fish-borne trematodes and/or their close relatives. Opisthorchiasis has been studied extensively in Thailand, where about 8 million people are infected with the liver fluke. Here we review the pathogenesis, control and re-emergence of O. viverrini infection, in particular in Thailand and, to a lesser extent in Lao PDR given the contiguous geographical range of O. viverrini through these two regions. We also review the association of O. viverrini infection and cholangiocarcinoma, bile duct cancer, and highlight new findings on pathogenesis of liver fluke-induced cholangiocarcinogenesis. Last, we comment on national control strategies in Thailand for the control of O. viverrini infection aimed at reduction in the prevalence of O. viverrini-associated liver cancer in the longer term.

Liver fluke infection and cholangiocarcinoma : Model of endogenous nitric oxide and extragastric nitrosation in human carcinogenesis

Cancers arising during bacterial, viral and parasitic infection provide useful models to investigate the link between inflammation and carcinogenesis. Because the inflammatory agent is known, relationships between immune responses, the production of DNA-damaging agents, such as nitric oxide, oxygen radicles and N-nitroso compounds, and cancer risk can be explored. This paper first describes the close relationship between infection with the liver fluke, Opisthorchis viverrini, and cholangiocarcinoma in humans. Data are then presented which demonstrate an elevation in levels of salivary nitrite and urinary and plasma nitrate among men with moderate and heavy liver fluke infections compared to uninfected controls which was absent 4 months after the parasites were cleared with praziquantel. Because of the strict control over subject selection and dietary intake plus the absence of the increase following treatment, we conclude that the higher levels of nitrate and nitrite reflect endogenous generation of nitric oxide resulting from liver fluke infection. Excess nitric oxide generation in the inflamed tissue is likely to lead directly to the formation of N-nitroso compounds mediated by activated macrophages. Further work will attempt to demonstrate a link between this increase and both parasite-specific immune responses and the risk of cancer.

Opisthorchis viverrini: an underestimated parasite in world health

Infection with Opisthorchis viverrini and its associated cholangiocarcinoma (CCA) is an underestimated problem in the Mekong region of Southeast Asia, despite the widespread use of praziquantel and health education measures for parasite control. Although data from Cambodia, Laos and Vietnam are rare, data from Thailand often show wide-ranging variability in epidemiological parameters, including human morbidity and the prevalence and incidence of CCA. The recent discovery of high levels of population genetic variability in O. viverrini in different wetlands in Thailand and Laos, which indicates the presence of sibling species, suggests that we have underestimated the complexity of this epidemiological situation. Future research should determine the relationship between the genetic variability of O. viverrini and patterns of opisthorchiasis-related disease.

Advanced periductal fibrosis from infection with the carcinogenic human liver fluke Opisthorchis viverrini correlates with elevated levels of interleukin‐6

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. (HEPATOLOGY 2009.)

A high frequency of hepatobiliary disease and suspected cholangiocarcinoma associated with heavy Opisthorchis viverrini infection in a small community in north-east Thailand

A group of 87 adults from a small village in north-east Thailand was chosen to undergo ultrasound investigation based on their intensity of infection with the liver fluke, Opisthorchis viverrini, or clinical status (history of jaundice, current hepatomegaly). From this group, 8 cases of suspected early cholangiocarcinoma were found, and the diagnostic features of 6 of the 8 were confirmed by computerized tomography scan and endoscopic retrograde cholangiopancreatography. In addition, several cases of mild gall-bladder disease, chronic cholecystitis, cholelithiasis and parenchymal liver disease were detected. A highly significant positive relationship between the intensity of liver fluke worm burden and the severity of biliary tract disease within individuals is reported. These results indicate that Opisthorchis is associated with moderate to severe hepatobiliary disease in a considerable proportion of infected individuals.

Roles of liver fluke infection as risk factor for cholangiocarcinoma

Several factors are known to be associated with risk of cholangiocarcinoma (CCA) and infection with the liver flukes, Opisthorchis viverrini and Clonorchis sinensis, has often been singled out as the leading risk factor in east and southeast Asia. In this review, current knowledge of their biology, life cycle, and pathogenesis of O. viverrini, and its role as a carcinogenic parasite are presented. The trends of age‐specific incidence of liver cancer in Khon Kaen, northeast Thailand are considered and compared with the prevalence profiles of O. viverrini. Potential impacts of the liver fluke control program particularly by mass drug administration (MDA) and public health education in the past and a recent drop of incidence of CCA are discussed in relation to primary prevention and control of this fatal bile duct cancer.

Relationship between faecal egg count and worm burden of Opisthorchis viverrini in human autopsy cases

The relationship between faecal examination for egg output and worm burden of Opisthorchis viverrini in man of 181 autopsy cases from Northeast Thailand is described. Diagnosis of the parasite infection by stool examination for the presence of eggs was less sensitive than the worm recovery technique. Using Stolls dilution and formalin-ether technique, no eggs were detected in the faeces of 20 cases harbouring low worm burdens (less than 20 worms). The quantitative faecal egg count by Stolls dilution technique showed a strikingly close positive correlation with the number of worms recovered (r = 0.96, P less than 0.001) indicating a strong linear association between eggs per gram of faeces (epg) and worm burden. The number of epg per worm was inversely correlated to the worm burden (P less than 0.001), suggesting that density-dependent constraints on fecundity could operate to restrict egg output in heavy infections. The accuracy of egg counts for estimating worm burden and its relevance to parasite epidemiological research are discussed.

The zoonotic, fish-borne liver flukes Clonorchis sinensis, Opisthorchis felineus and Opisthorchis viverrini

Clonorchis sinensis, Opisthorchis felineus and Opisthorchis viverrini are the three most important liver flukes involved in human health, infecting more than 45 million people worldwide. Both C. sinensis and O. viverrini, and possibly O. felineus, can induce human cholangiocarcinoma as well as inducing other hepatobiliary pathology. Although the life cycles of all three species are similar, only that of O. felineus in Europe remains predominantly zoonotic, while O. felineus in Asia and C. sinensis have a stronger mixture of zoonotic and anthroponotic components in their life cycles. Opisthorchis viverrini from the Mekong area of southeastern Asia is predominantly anthroponotic. Here we discuss the comparative epidemiology of these three taxa comparing in detail the use of first, second and final animal hosts, and consider the potential role of humans in spreading these pathogens. In addition we discuss the genetic structure of all three species in relation to potentially cryptic species complexes.