Filariasis transmission in Samoa. II. Some factors related to the development of microfilariae in the intermediate host.

The developmental period of microfilariae of sub-periodic Wuchereria bancrofti in laboratory-bred Aedes polynesiensis and Ae. samoanus was shorter in the warm season (December to May) than in the cool season (June to November). In the warm season the microfilariae reached the 'sausage' stage in three days, cylindrical second stage in seven days and the infective stage in 12 days after the infecting meal. During the cool season the incubation period was extended to 14 days. Microfilariae persisting in a carrier recently treated with diethylcarbamazine citrate readily infected Ae. polynesiensis and Ae. samoanus and developed into the infective stage, but the proportion which became infected was significantly less than the proportion infected on an untreated carrier having comparable microfilarial density. Under the conditions of the experiments the survival of infected Ae. polynesiensis and Ae. samoanus was dependent on physical conditions. The average level of infective worm burden did not appear to affect the mortality of the vectors.