Tanzania: control of Culex vectors of filariasis

Abstract

The construction of pit latrines or septic tank/cesspit sanitation systems frequently leads to an upsurge of Culex quinquefasciatus mosquitoes, which breed in organically polluted water. These are the main nuisance mosquitoes and vectors of filariasis (which leads to elephantiasis and hydrocele) in tropical urbanised areas. Mosquito larvae and pupae breath air through the water surface and, as originally suggested by Paul Reiter, a floating layer of expanded polystyrene beads suffocates the larvae and pupae and is very durable. The town of Makunduchi, Zanzibar, Tanzania (population 12 000) was notorious for its mosquitoes and filariasis until 1988 when, with a team of three local malaria agents, we located all 550 wet pit latrines, expanded enough polystyrene from imported granules in boiling water (figure) and treated all the pits with a layer 1–2 cm thick. This brought down the density of mosquitoes in bedrooms by 98%.1Maxwell CA Curtis CF Hamadi Haji Shaban Kisumku Abdul Issa Thalib Salum Ali Yahya Control of bancroftian filariasis by integrating therapy with vector control using polystyrene beads in wet pit latrines.Trans R Soc Trop Med Hyg. 1990; 84: 709-714Summary Full Text PDF PubMed Scopus (76) Google Scholar Almost simultaneously we arranged mass treatment of the people with the antifilarial drug diethylcarbamazine. percentage of people with microfilariae in night blood samples declined from 49% before treatment to 10% soon after it and then to 3% over the next five years. During this time there was no further drug treatment, but the chances of reinfection were kept very low by periodic checks for, and treatment of, new breeding places in pit latrines. Unfortunately, checks have not been kept up in the past four years and people are once again complaining of mosquito nuisance. A check of night bloods was done in 1997 (results not yet in). Arrangements are in hand to send a new supply of expandable polystyrene and to revive the system of checking and where necessary treatment of newly wet pit latrines. Makunduchi is exceptional in having no drains and almost no marshes in which mosquito breeding can occur (and for which polystyrene beads are not applicable). However, in many tropical towns and refugee camps long-term prevention of mosquito breeding in the pits with polystyrene beads would give control teams the time to concentrate their effort on repeated treatment, with chemical or bacterial agents, of more open sites.