Date Published: May 28, 2008
Publisher: Public Library of Science
Author(s): Banchob Sripa, Alex Loukas
Partial Text: Human liver fluke infection caused by Clonorchis sinensis, Opisthorchis viverrini, and O. felineus remains a major public health problem, affecting the poor in the poorest regions of Asia. An estimated 45 million people are infected and more than 600 million are at risk of these infections ,. This Viewpoint highlights the distribution of the infection, clinical features, neglect of liver fluke infection, and how the global health community can help to eradicate the infection in Asia.
Most of those infected with liver fluke live in Asia. C. sinensis is endemic in south China, northern Vietnam, Taiwan, and Korea, while O. viverrini is found mainly in Thailand, Lao People’s Democratic Republic (PDR), Cambodia, and central Vietnam. In Northeast Thailand and Laos, despite widespread administration of the anthelmintic drug praziquantel, the prevalence of O. viverrini approaches 85% in endemic areas in Lao PDR . A recent survey in the Chi River basin in northeast Thailand found a prevalence of O. viverrini of up to 78% in certain villages (B. Sripa, T. Laha, J. Bethony, P. J. Brindley, et al., unpublished data). An estimated 6 million people in Thailand are infected with Opisthorchis.
Liver fluke infections are associated with several hepatobiliary diseases, including cholangitis, cholecystitis, gallstones, hepatomegaly, and cholangiocarcinoma (CCA), the primary liver cancer that arises from biliary epithelial cells . Opisthorchis is one of two helminth parasites (O. viverrini and Schistosoma hematobium) that are carcinogenic to humans, as reported by the World Health Organization and the International Agency for Research on Cancer . In Thailand, CCA is the most prevalent of the fatal neoplasias, and liver and bile duct cancer ranks at number five in the list of diseases in Thailand that cause the highest number of disability adjusted life years (DALYs) . CCA is responsible for about 15%–25% of liver cancers in the United States but represents 86.5% of all cancers in Thailand’s Khon Kaen region, the highest incidence in the world (Figure 1) .
Despite the high prevalence of liver flukes in Asia, and the associated hepatobiliary disease, these infections are relatively neglected, not only by national governments but also by international health organizations and granting agencies. Because of the rapid economic growth during the past decade in Asia, an epidemiological transition has occurred—there has been an increase in “Western” life styles (such as adopting Western diets) and a rise in the so-called chronic diseases of affluence, particularly in the middle class population. For example, in Thailand, the top four causes of death in the year 2004 were heart disease, diabetes, hypertension, and cancer . The Thailand National Health Strategic Plan 10 (2007–2011) therefore mainly focuses on these diseases and emerging infections, i.e. avian influenza, HIV/AIDS, influenza, and tuberculosis (TB) . Other infectious diseases with high morbidity/mortality such as malaria, dengue, leptospirosis, filariasis, and leprosy are always on the list of priorities of the Ministry of Public Health . However, asymptomatic parasitic infections, including those caused by liver fluke, that affect the poor and poorest people (i.e., the majority of the population) have received less attention. A major Thai campaign to eliminate liver fluke that was operational a decade ago has now disappeared, even though the infection is still endemic in northeastern and northern parts of Thailand . Similar situations have been described in other liver fluke endemic countries of Asia .