Filariasis in Thailand.

Endemic filariasis in Thailand is restricted to the flat, low-lying, rural areas in the eastern coastal belt of peninsular Thailand. A large number of villages was surveyed, and 4,112 persons were examined, of whom 863 were found to be positive for microfilariae in the peripheral blood and 215 to have filarial disease. The chief manifestation was elephantiasis of the leg, which was sometimes associated with elephantiasis of the arm. The causative organism of endemic filariasis in Thailand is Wuchereria malayi.Nine species of mosquito (four of Mansonia and five of Anopheles) are vectors of W. malayi infection in Thailand. They are found naturally infected with the larval stages of W. malayi, the infection rates in the different vector species ranging between 3% and 17%. These mosquitos occur in large numbers and breed in the extensive marshes in the vicinity of the villages.The author discusses the feasibility of different measures for the control of filariasis. Under the conditions prevailing in the endemic areas of Thailand, the author considers that halting transmission by spraying dwellings with residual insecticides would be feasible as well as economical. This method was tried experimentally in a restricted area, and it was found that spraying all dwellings in a village with DDT, in a dosage of 170 mg per square foot (approximately 1.8 g per m(2)), effectively controlled the transmission of filarial infection and considerably lowered the incidence of vector mosquitos.