デング熱媒介蚊に関する一考察 : 1942-1944 年の日本内地のデング熱流行におけるヒトスジシマカ Aedes albopictus およびネッタイシマカ Aedes aegypti の意義について Dengue vector mosquitoes in Japan : The role of Aedes albopictus and Aedes aegypti in the 1942-1944 dengue epidemics of Japanese Main Islands
In August 1942 dengue fever broke out in Nagasaki, a port city located in the Kyushu District, Japan. It soon spread over other cities, recurring every summer until 1944. This was not only the first dengue epidemic in Japan proper but also was one of the most widespread dengue epidemics recorded in a temperate region, involving at least 200,000 typical cases. It was obvious that the principal vector was Aedes albopictus which distributes in the Main Islands of Japan, particularly south of 38-39°N. At that time an important factor promoted transmission of the infection. A number of water tanks had been set up for the purpose of extinguishing fires caused by bombardment during the war, and the tanks were occupied by innumerable mosquitoes. Large-scale application of insecticides was not then possible. Since the early work by Yamada (1917a, b), it had been believed that Ae. aegypti mosquitoes do not habit in Japan proper, excepting the Ryukyu and Ogasawara Islands. Contrarily, Oguri (1945) and Oguri and Kobayashi (1947,1948) reported that they found Ae. aegypti in the Ushibuka area of Kyushu (32°N) during September 1944 to May 1947. Several other investigators obtained similar survey data as those of Oguri and Kobayashi (1947,1948). The species, either adults or larvae, completely disappeared, however, from there after 1955. In another survey it was observed that, inside a cargo boat which plied between Japan and dengue-prevalent Southeast Asian countries, many Ae. aegypti were seen flying and also larvae were caught from small water deposits on the decks. It was thought that Ae. aegypti were transferred into Japan probably by boat, and that the mosquito settled in a particular area of Japan for several years. There was no definite evidence as to whether or not the imported Ae. aegypti had some role in the 1942-1944 Japanese dengue epidemics. However, serious precautions must be taken against the possible danger that vectors of infectious diseases may be introduced into an originally non-endemic area. Biological and epidemiological aspects relative to these problems are discussed.