Vector Mosquitoes of Filariasis in Japan

The main vector of Brugia malayi in the small endemic focus on Hachijo-koshima Island was determined to be Ochlerotatus togoi (as Aedes togoi) [1]. As to Wuchereria bancrofti, many species of mosquitoes were experimentally examined for susceptibility in the laboratory as by Mochizuki in 1911 and 1913 [2, 3], Yamada in 1927 [4], Fujisaki in 1958 and 1959 [5, 6], and Omori in 1962 [7]. The results indicated that among 26 mosquito species tested Culex pipiens pallens, Cx. pipiens molestus, Cx. Pipiens quinquefasciatus, Cx. vagans, Cx. whitmorei and Ochlerotatus togoi (as Aedes togoi) were highly susceptible (the microfilaria could develop to the infective stage in the body of mosquitoes in high rates), while Cx. bitaeniorhynchus, Cx. pseudovishnui (as Cx. vishnui), Cx. sinensis, Cx. tritaeniorhynchus, Anopheles sinensis and Armigeres subalbatus had extremely low susceptibility [8]. Of the highly susceptible six mosquitoes, Cx. pipiens molestrus, Cx. vagans and Cx. whitmorei were excluded from important vectors of bancroftian filariasis in Japan, because they were rather rare at least in filariasis endemic areas and no natural infections were observed [9]. Oc. togoi, which breeds almost exclusively in rock pools near the sea, was common in some coastal areas, for example, in Goto Islands of Nagasaki prefecture, and the natural infection with the parasite was not rarely observed. However, because of rather poor anthropophily in blood feeding habit [10] this mosquito was regarded only as the secondary vector even in particular coastal areas where the density was quite high. The remaining two mosquitoes, Cx. pipiens pallens and Cx. pipiens quinquefasciatus, were the most important vectors transmitting bancroftian filariasis in Japan. They are taxonomically different only in subspecific status, and the former is distributed in Kyushu Island and further north and the latter in Amami-Oshima Island and further south. The both mosquitoes with similar biological characteristics were always very common in dwelling houses in areas endemic for bancroftian filariasis and very anthropophilic in blood feeding, and the natural infections with W. bancrofti were frequently found. The main breeding places were drains receiving domestic waste water and manure pits.