Opisthorchiasis control in Thailand.

History of opisthorchiasis control started in 1950 as a small scale helminthiasis control program in some high risk areas. Following a number of studies and trial projects of the Faculty of Tropical Medicine, Mahidol University, the national liver fluke control program has been developed and operated under several National Public Health Development Plans. Presently, the program is being operated in some provinces of the Central, and all provinces of the Northeast and North of Thailand. The main strategies for liver fluke control comprise of three interrelated approaches, namely stool examinations and treatment of positive cases with praziquantel for eliminating human host reservoir; health education for a promotion of cooked fish consumption to prevent infection, and the improvement of hygienic defecation for the interruption of disease transmission. Between 1984 and 1987, the positive rate of liver fluke infection was 63.6%. In 1988, the positive rate went down to 35.6%. Following the region wide control program started in 1989, the annual positive rates had subsequently decreased to 9.4% in the year 2001. The prevalence rate was remarkably high in the North and moderately high in the Northeast, while the prevalence in the Central region was considerably low and there was no evidence of disease transmission in the South.