PARASITE-ASSOCIATED MORBIDITY - LIVER FLUKE INFECTION AND BILE-DUCT CANCER IN NORTHEAST THAILAND

Infection with the liver fluke, Opisthorchis viverrini, remains a majo r public health problem in Northeast Thailand, where approximately one -third of the population is infected. The northeast region is largely populated by Laos-descendent Thais who enjoy eating raw fish, which ha rbour the infective stage of the fluke. The parasite has maintained it s presence in the population despite the widespread use of praziquante l and dissemination of health education material throughout the region by vigorous government-sponsored programs in recent years. The most s evere consequence of liver fluke infection is cholangiocarcinoma, i.e. cancer of the bile duct epithelium. Although mortality due to the par asites alone appears to be uncommon, cholangiocarcinoma arising as a r esult of infection is one of the leading causes of death in the region . This paper reviews the pathogenesis of infection and the geographic, hospital-based and community studies which demonstrate the close rela tionship between infection and cancer. In addition, data from the Canc er Registry of Khon Kaen, Northeast Thailand and population-based stud ies using ultrasonography to Visualize early tumours which illuminate the very high frequency of the cancer among heavily infected individua ls and communities are discussed. Finally, the paper will close with a brief commentary on the prospects for control of the parasite and its likely impact on the frequency of cancer given the current epidemiolo gical situation of liver fluke infection.