Malaria: increases in mortality due to climate change

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Malaria is of great public health concern, affecting nearly half of the world’s population, the majority of who reside in poor developing countries located in the tropical and subtropical climate. According to the World Health Organization (WHO), the death burden of malaria, a vector-borne disease transmitted by the bite of infected arthropod species such as mosquitoes, has increased over the last decade. In 2016, an estimated 445,000 deaths and 216 million cases of malaria occurred worldwide, while 70% of the deaths occurred in children under five years old.
Moreover, changes in climatic exposures such as temperature and precipitation make malaria one of the most climate sensitive outcomes. Changes in temperature, for example, influence the incubation period of malaria parasites and in turn malaria transmission rates: the minimum and maximum temperature for the survival of Plasmodium falciparum are 18 °C and 40 °C, respectively, thus at relatively higher temperature levels, less time is required for parasite development, which increases probability of spreading infection. Rainfall often leads to stagnant water critical for breeding of mosquito eggs.

A study published on International Journal of Hygiene and Environmental Health realized by Shouro Dasgupta, CMCC researcher at ECIP Division, investigated the relationship between climatic exposure (temperature and various measures of extreme precipitation) and malaria mortality while using a global dataset for 105 countries over a span of 30 years (1980 – 2010). Researcher S. Dasgupta computed optimal climatic conditions that maximize malaria mortality and provided projections of future burden of malaria due to climate change.

Results highlighted that the relationship between temperature and malaria mortality is non-linear: as temperature increases, malaria mortality initially declines but as temperature crosses a threshold, malaria mortality increases. The estimated global temperature optimum beyond which total malaria mortality increases is 20.8°. Most countries in Sub-Saharan Africa have annual mean temperatures between 20 °C and 28 °C – hence containing the optimum conditions to maximize malaria related mortality. Moreover, in the case of child mortality, the study underlines a significantly lower threshold of 19.3 °C, and this is highly critical as the majority of malaria related mortality occurs among children. In the continents where malaria is most prevalent, Africa and Asia, the threshold beyond which malaria mortality increases is 28.4 °C and 26.3 °C, respectively.
By the end of the 21st century, the author estimates that unmitigated climate change will increase all-age malaria mortality by 2.6%. All-age malaria mortality is projected to increase in all the countries where malaria is currently present, with Sri Lanka and Philippines experiencing the highest increases.
Furthermore, the research estimates that child mortality (ages 0–4) is likely to increase by up to 20% in some areas due to climate change by the end of the 21st century. The projected increase for child mortality is significantly higher due to the lower optimal temperature.

The results of this research might be used to reduce the burden of malaria for example by targeting regions that are close to the threshold temperature with additional malaria eradication and transmission control efforts. Projections can be used to develop early warning systems in areas that are expected to experience increases in malaria mortality due to climate change.

For more information, read the integral version of the paper:
Dasgupta S. Burden of climate change on malaria mortality, 2018, International Journal of Hygiene and Environmental Health, DOI: 10.1016/j.ijheh.2018.04.003

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