Field studies on the control of malayan filariasis and its vector mosquitoes in Hachijo-Koshima Island

Sasa Manabu, Hayashi Shigeo, Suzuki Takeshi, Miura Akiko, Ueno Yoji, Tanaka Hidebumi

doi:10.7601/mez.8.5

In the present paper, the authors report on the results of field studies on the control of malayan filariasis prevalent among the inhabitants of Hachijo-koshima Island which is located about 360km south of Tokyo. It has been known since old times that a kind of elephantiasis exists in this area, but it was 1951 that the causative parasite was identified as Wuchereria malayi (Brug, 1927) by the authors and their associates. Among the six species of mosquitoes found in this island, Aedes togoi was demonstrated to be naturally infected by the worm and acted as the main vector of the disease, and Culex pipiens pallens was also found to harbour the infective larvae of the parasite in experimental studies. The present study was designed to erradicate the disease from this area both by the treatment of human carriers and by the control of mosquito vectors. The projects started from August 5, 1956 with the examinations of thick blood smears of the inhabitans for the microfilariae. Out of 66 persons 22 or 33.3% were found to be positive. "Supatonin" (diethyl carbamazine compound) was administered to all of the carriers by the ratio of 6mg per kilogram of body weight daily for 14 days. Through previous studies, the drug was certified to be a very effective chemotherapeutic, but to cause febril attacks on the first few days of the course. As for the mosquito control, various measures were adopted simultaneously. DDT residual spray was applied to the total of 25 houses by the ratio of 2g of DDT to 1 square meter of the walls, using water suspension of 40% DDT paste manufactured by Nippon Soda Co. This immediately caused the practical erradication of adult mosquitoes and houseflies from the human dwellings. Breeding places of mosquito larvae were treated in different ways according to the types of water. Concrete rain-water reservoirs were the main source of the vector species, to which a kind of small fresh-water fish, Oryzias latipes (Temminck et Schlegel) carried from Tokyo or naturally bred at Hachijo Island was set free. Through previous experiments, the fish was found to erradicate mosquito larvae from the reservoirs. Miscellaneous water containers scattered in the village were treated by suspensions of DDT paste by the ratio of 1 ppm of DDT to the amount of water. Thousands of rockpools were also found to be scattered along the shore and to harbour large numbers of larvae of Aedes togoi. To this area, DDT dusting by a helicopter Bell-47-G was applied. A total of 180kg of 10% DDT powder was applied to an area of about 80, 000 sqare meters. All of the larvae examined after 24 hours were found to be killed by the insecticide. The island was again surveyed in December of the same year. The radical control of neither the parasite nor the vectors has not yet been attained. It was suggested that repeated applications of such control measures were needed to accomplish the purpose.

Field studies on the control of malayan filariasis and its vector mosquitoes in Hachijo-Koshima Island

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