Randomized trial of spatially targetted control to virtually eliminate malaria

Lead Research Organisation: University Cheikh Anta Diop de Dakar

Abstract

There has recently been a sharp decline in the incidence of malaria in several parts of Africa, due to the strengthening of control measures, most importantly the large-scale distribution of free and highly subsidized insecticide-treated bednets, raising the prospect that malaria could be eliminated. But despite scaling-up of control, transmission persists in foci which provide a continuing source of infection. Additional strategies are needed to eliminate these foci, this is important because a resurgence of malaria in populations whose acquired immunity has lapsed could have a devastating impact. The aim of this study is to find out whether we can virtually eliminate malaria in a population by delivering intensified control in villages with persistent transmission. The trial, which will take place in central Senegal, will run over two years. Each year we will select villages to be targeted, on the basis of malaria cases reported in the previous year, and we will operate intensified malaria control in these villages, attacking the vector population with indoor residual spraying with a highly effective residual insecticide, and treating infected persons with effective antimalarial drugs to remove the reservoir of infection. The hope is that by targeting the places which favour transmission, there will be reduction in the prevalence of malaria infection not only in areas which are targeted but also in the surrounding villages that are not targeted. Spraying is done just before the rainy season begins, coating the places where the first mosquitoes to emerge will rest, to kill them before they can transmit infection. Chemotherapy will be done once early in September, to clear the reservoir of infection in humans before the height of the transmission season, and again in October to clear any persisting or new infections. We will use a combination of two drugs, an artemisinin to quickly clear malaria infection, and piperaquine, which provides prophylaxis for about a month. Treatment of carriers is known to be an essential component of elimination programmes but it is an open question whether it is better to administer antimalarial drugs to all members of the community or screen and treat only those who are positive. The trial will use both approaches to see which is most effective and practical. It is hoped that the findings of this study will contribute to the elimination of malaria in areas where until recently it was the major cause of child deaths.

Technical Summary

In Senegal as in other parts of African malaria there has been a dramatic decline in the incidence of malaria associated with scaling up of the distribution of insecticide treated bednets. However malaria transmission persists in foci which provide a continuing source of infection. Elimination of these foci is an important priority because a resurgence of malaria could have a devastating impact. The purpose of this trial is to evaluate the extent to which intensified malaria control, employing indoor residual spraying (IRS) with insecticide and chemotherapy, targetted to villages with persistent transmission, can virtually eliminate malaria in an area in central Senegal, and to determine whether, as part of this strategy, chemotherapy should be delivered to all members of targetted communities or only those who have been tested and are known to be infected. The unit of randomization will be the health post and the population of approximately 10,000 people that it serves. 40 health posts will be randomized, 15 will operate targeted malaria control with IRS followed by screening of all persons and treatment of those who are positive, 15 will operate targeted control with IRS followed by treatment of all persons without screening, and 10 health posts will serve as controls. The interventions will be delivered over two transmission seasons and the primary endpoint will be the prevalence of P.falciparum measured in a survey of the population at the end of the second season. Incidence of clinical cases of malaria will be monitored by passive detection by health staff. Costs of delivery and acceptability of the interventions will be important secondary outcomes. The impact of the interventions on vector susceptibility to insecticide and the prevalence of drug resistant parasites will be monitored.

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