Epidemiological Status of Opisthorchis viverrini Metacercariae in Freshwater Fish Across the Greater Mekong Subregion
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Abstract
Opisthorchis viverrini (a Group 1 biological carcinogen) remains a major public health problem in the Greater Mekong Subregion because of its strong association with cholangiocarcinoma. Given that human infection mainly occurs through the consumption of raw or undercooked cyprinoid fish containing infective metacercariae. This review summarizes the epidemiological status, geographical distribution, host specificity, and transmission dynamics of O. viverrini metacercariae in cyprinoid fish across Thailand, Lao People’s Democratic Republic (Lao PDR), Cambodia, Myanmar, and Vietnam. The reviewed studies demonstrated considerable geographical variation in O. viverrini metacercariae prevalence throughout the Greater Mekong Subregion, with particularly high endemicity reported in Cambodia and Lao PDR, especially within Mekong River-associated ecosystems. In Cambodia, prevalence reached 90.2% in cyprinoid fish from Kandal Province, whereas substantially lower prevalence levels were generally observed in inland regions of Thailand. Species-specific variation was also evident, with Cyclocheilichthys spp., Hampala dispar, and Systomus orphoides identified as important second intermediate hosts in the transmission cycle of O. viverrini. Seasonal fluctuations, aquatic ecology, environmental contamination, and inadequate sanitation were consistently associated with transmission intensity. The available evidence indicates that O. viverrini metacercariae remain widely distributed in freshwater ecosystems across the region, reflecting the persistent risk of fish-borne transmission in endemic communities. Strengthened surveillance of high-risk cyprinoid fish species, improved sanitation, and sustained behavioral interventions remain essential for reducing transmission and the long-term burden of cholangiocarcinoma in the region.
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