Surveillance of imported bancroftian filariasis after two-year multiple-dose diethylcarbamazine treatment.

Myanmar migrants are at increased risk for nocturnally periodic Wuchereria bancrofti causing imported bancroftian filariasis. They have a significant influence on the effectiveness of diethylcarbamazine (DEC) mass treatment at the provincial level in the National Program to Eliminate Lymphatic Filariasis (PELF) during the fiscal years (FY) 2002-2006, in Thailand. Two oral doses of DEC 6 mg/kg are given twice a year to the eligible Myanmar migrants (> or = 2 years old). A 300 mg DEC provocation test is given once a year to all Myanmar migrants with work permits. Effectiveness evaluation parameters, such as cumulative index (CI) and the effectiveness ratio (ER), were obtained after 2 years of the multiple-dose DEC treatment program in Ranong Province, Southern Thailand. By cross-sectional night blood surveys at the end of FY 2003 in two districts of Ranong Province, the microfilarial positive rates (MPR) were 0.8% and 1.2% for Mueang Ranong and Kra Buri, respectively. The MPR in the agricultural (1.5%) and industrial (0.4%) occupations were not significantly different from each other. Our findings suggest that most untreated microfilaremics working in agriculture, with short-term residency in Thailand, may have delayed multiple-dose DEC treatment.