Control of Bancroftian filariasis by integrating therapy with vector control using polystyrene beads in wet pit latrines

In the town of Makunduchi, Zanzibar, wet pit latrines provided breeding places for Culex quinquefasciatus and there were few other mosquito breeding places available. The adult mosquito population in bedrooms was monitored for a year and found to consist almost entirely of Cx quinquefasciatus of which 2.45% carried infective larvae of Wuchereria bancrofti. It was estimated that each person received about 24,993 bites per year, of which 612 were potentially infective. After a year of baseline data collection, polystyrene beads were expanded in boiling water and applied to form floating layers on all infested pits. Subsequently the adult mosquito population declined remarkably so that the estimated number of bites per person per year was only about 439. To retain control, surveillance for newly wet pits continued to be necessary. Initially the microfilarial rate in the human population was 49.5%, with many cases of filarial disease. The microfilarial rate was reduced to 10.3% by mass treatment with diethylcarbamazine, with no sign of resurgence a year after treatment. The infective rate among mosquitoes was reduced to 0.41% and the combined effect of the vector and microfilarial control was to reduce the number of infective bites per person per year by 99.7%.