Epidemiology of opisthorchiasis and national control program in Thailand.

Opisthorchiasis is a disease caused by opisthorchis trematode commonly known as liver fluke. In Thailand Opisthorchis viverrini is the only parasite of opisthorchiasis, the first case of opisthorchiasis was reported in 1911 by Leiper from the autopsy of corpse in Chiang Mai. Later on Sadun in 1953, Harinasuta and Vajjarasthira in 1961, and Wykoff in 1965 had demonstrated a complete life cycle of O. viverrini. History of opisthorchiasis control has dated back to 1950 as a small scale helminthiosis control program in some high risk areas. Following a number of studies and trial projects of the Faculty of Tropical Medicine of Mahidol University, the national liver fluke control program has been developed and operated under different National Public Health Development Plans. Presently, the program is being operated in some central provinces, and all northeastern and northern provinces of Thailand. The main strategies for liver fluke control are comprised of 3 interrelated approaches, namely stool examination and treatment of positive cases with praziquantel for eliminating human host reservoir; health education for a promotion of cooked fish consumption for preventing infection; and the improvement of hygienic defecation for transmission interruption. Data obtained from liver fluke control operation in 1996 show the countrywide prevalence of opisthorchiasis at 21.5% with a variation in all age groups. Differences of infection are also found among geographical regions. A large percentage of infection is mild infection. Comparing figures of 1981 and 1991, there is a considerable increase in the central and northern regions, while the northeastern region has significant decrease.