State of the Planet

News from the Columbia Climate School


Seasonal Changes in Climate May Muddle Results of Malaria Interventions in Africa

Infant in a malaria bed net. Photo: World Bank Photo collection
Infant in a malaria bed net. Photo: World Bank Photo collection

New studies released today in a special supplement of the American Journal of Tropical Medicine and Hygiene add to the evidence that over the last decade, global malaria control efforts have saved millions of children’s lives in the areas most affected by the mosquito-borne disease.

Some of the studies, including one conducted by Columbia University’s International Research Institute for Climate and Society (IRI), present new methods for evaluating large-scale malaria control programs.

Malaria remains a major cause of preventable death, killing an estimated 429,000 people and causing more than 212 million illnesses in 2015, according to the World Health Organization. Hundreds of millions of people have benefited from protective measures, such as insecticide-treated bed nets and spraying of homes with insecticides, and have been appropriately diagnosed with rapid tests and treated with effective anti-malarial drugs.

The journal’s September 2017 supplement includes nine novel contributions on evaluating the impact of malaria control interventions in sub-Saharan African countries, where the majority of malaria deaths are among children under the age of five years.

The IRI-led study assesses the likely impact that changes in climate have on assessments of the effectiveness of national malaria interventions in ten of these countries.

“Malaria is a climate-sensitive disease, meaning that natural fluctuations in rainfall and temperature conditions from one season or one year to the next can have a significant impact on the suitability for transmission of the disease,” said IRI’s Madeleine Thomson, who led the research.

“Warm temperatures, rainfall, and humidity determine the geographical distribution, seasonality and prevalence of the disease,” explained Julie Wallace, who is the head of the malaria division at the U.S. Agency for International Development’s Global Health Bureau.

Thomson and her colleagues found that out of the ten countries they examined, three—Tanzania, Zanzibar and Uganda—may be overestimating the impact of malaria control efforts. Unusually wet conditions during the baseline (or control) period and droughts during the intervention period may have contributed to the observed malaria decline.

In contrast, the team found that Mali, Senegal, and Ethiopia may be underestimating the impact of their control efforts. In these countries, the intervention periods faced wetter conditions than the baseline periods. In general, wet conditions increase the likelihood of standing water and higher humidities, which leads to upticks in mosquito populations that transmit the disease.

In the remaining four countries—Rwanda, Malawi, Mozambique, and Angola—Thomson and her colleagues could find no strong difference in climate conditions between the pre- and post-intervention period.

The results show that “It is important for the President’s Malaria Initiative to ensure that when we evaluate the impact of country malaria control activities, we consider climate in our analysis,” said Wallace.

Read the full story on the IRI website.

Media contact: Francesco Fiondella, francesco @, +1-646-321-2271

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