Engineering a solution to malaria in the Sahel

January 2009

PROBLEM

Ephemeral, rain-fed pools of water facilitate malaria mosquito breeding in the African Sahel, whose inhabitants suffer more than 80 percent of the world’s malaria deaths. Attempts to control malaria through the distribution of insecticide-treated bed nets have significant sustainability problems, including donor fatigue and development of insecticide resistance accompanied by a change in mosquito biting habits from indoor nighttime biting to outdoor daytime feeding. MIT researchers believe that environmental changes to the landscape can provide a means for controlling malaria at the village scale in a financially sustainable, ecologically sound manner.

APPROACH

A coupled hydrology and entomology model, created by Professor Elfatih Eltahir and Arne Bomblies, precisely represents the physical environment where malaria vector mosquitoes breed, and simulates breeding and biting behavior.

While traditional models correlate monthly rainfall with malaria incidence, this new model represents the physical environment in terms of topography, vegetation, soil type and time-variable rainfall for an area surrounding the village of Banizoumbou, Niger, where about 40 percent of people are infected with the malaria parasite at any time. The entomology model tracks characteristics relevant to malaria transmission to individual mosquitoes. Mosquitoes are given a modicum of freewill in breeding and biting behavior in response to the 1,000 people living in the area. (A mosquito’s movements, while wind-dependent, also follow the plume of human emanations such as breath and odor.) The model simulates the entire life cycle of the mosquitoes, their infection with malaria, its transmission between humans and mosquitoes, and the presence of other animals serving as meal hosts.

To validate their model, Bomblies and Eltahir collected field and climate data during the rainy seasons of two years. Data included adult mosquito abundance, observation of pools, and meteorological and soil moisture measurements. Precipitation in the wet season of 2005 was sporadic and earlier than in 2006, which saw a 16 percent increase in rainfall, most of it heavy over a two-month period. These differences created significant variability in the size and duration of the ephemeral pools for the two years, and subsequently, in the mosquito population. Using these data, the model reproduced accurately the observed mosquito population dynamics for those years.

FINDINGS

The model can predict mosquito-dynamics response to simple changes in the landscape. Graduate student Rebecca Gianotti used the model to screen impact of two environmental management methods—ground leveling and increasing surface permeability—on malaria control in Banizoumbou, with positive effect. These methods reduced pool persistence to durations shorter than the aquatic development period of mosquitoes, preventing the emergence of adults. Such simple, effective, yet ecologically sound environmental modifications aimed at source reduction suggest that an environmental engineering approach offers villagers a sustainable method for combating malaria, in addition to the short-term protection afforded by other methodologies.

IMPACT

This new mechanistic model of malaria transmission offers an additional tool for addressing two important problems: development and testing of new environmental management strategies to combat the spread of malaria—one of the world’s major health challenges; and prediction of the impact of future climate change on malaria transmission in Africa.

MORE

An article about this research appeared in the Dec. 28 issue of the New York Times and in the Dec. 31 issue of Water Resources Research. Bomblies, now an assistant professor at the University of Vermont, was named one of SEED magazine’s “revolutionary minds” in 2007.

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