Infection and re-infection rates of opisthorchiasis in the water resource development area of Nam Pong project, Khon Kaen Province, northeast Thailand.

A one-year investigation on re-infection rates of opisthorchiasis was carried out in three villages in the Nam Pong Water Resource Development Project, Thailand. In the two villages where selective population chemotherapy was combined with improvements in sanitation and health education aimed at changing food habits, the mean monthly re-infection rate was 2.0% and the annual cumulative rate was 21.5%. In the third village, where only selective population chemotherapy was carried out, the monthly re-infection rate was 5.0% and the annual cumulative rate was 55.5%. Studies on new infections in initially negative individuals were also carried out in the three villages, with inconclusive results.

A pilot project for controlling O. viverrini infection in Nong Wai, Northeast Thailand, by applying praziquantel and other measures.

In a pilot control project of Opisthorchis viverrini in the village of Nong Wai Irrigation Area, Khon Kaen, Northeast Thailand, selected population based chemotherapy with a single dose of 40 mg/kg of praziquantel (2 - cyclohexylcarbonyl-1,2,3,6,7,11 b-hexahydro-4H-pyrazino [2,1-a]isoquinolin-4-one,EMBAY8440,Biltricide) was given to the stool positive cases once a year for a period of 3 years commencing May 1981. Two villages (pop 942) with a prevalence of 58.3% were used as tests villages and another one (pop. 442) with a prevalence of 55.1% served as control. The project programme integrated chemotherapy, sanitation improvement and health education, whilst only chemotherapy was applied in the control village. Among the 736 cases of all villages, 666 were treated in the first year and the parasitological cure rate after one month was 95.9%. Side effects of praziquantel were minor and were minimized by changing the time of drug intake from morning to after dinner. After one year the prevalence of opisthorchiasis was 36.8% in the test villages and 54.8% in the control village. The study on re-infection rate revealed that the average monthly incidence rate among the population in the test villages was 2.0% per month (range 1.1-5.0%) whereas it was 5.0% per month (range 1.9-10.3%) in the control village. In May 1982, second treatment was given again to the positive cases in the three villages with the same dose. The second year evaluation is in progress.

Mass treatment of opisthorchiasis in Northeast Thailand.

In an attempt to control opisthorchiasis, a single dose of 40 mg/kg of Praziquantel was given to 666 people in the three villages of Nam Pong Water Resource Development Project, Khon Kaen, Northeast Thailand. The results showed a cure rate after 1 month was 95.9%. The side effect was minimized by alternation of the time of treatment from after breakfast to after dinner. The use of Praziquantel for the mass treatment in control of opisthorchiasis is possible. However, to achieve the objective of control programme other measures such as environmental sanitation improvement, health education and change in eating habits must be integrated into the programme.