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Climate Change is a Relatively Insignificant Factor in Malaria Transmission and Outbreaks

Paper Reviewed
Zhao, X., Smith, D.L. and Tatem, A.J. 2016. Exploring the spatiotemporal drivers of malaria elimination in Europe. Malaria Journal 15: 122, DOI 10.1186/s12936-016-1175-z.

One of the concerns about CO2-induced global warming is the possibility that warmer temperatures will lead to an expansion of vector-borne diseases into cooler regions of the globe where they are not endemic. There are also fears that some diseases, like malaria, will regain a foothold into areas where they have previously been eradicated if temperatures rise as predicted by the models. Thus it is important to understand the many factors, including climate, that are thought to play a role in the transmission and outbreak of such diseases so that societies will be better prepared to meet the challenges that may lie ahead in this regard.

Leading out in just such an effort is the scientific trio of Zhao et al. (2016), who recently published a paper that quantified the impact of a range of factors that led to freeing Europe from endemic malaria transmission over the course of the 20th century. More specifically, the authors analyzed a range of spatial datasets representing climatic, land use and social-economic factors thought to be associated with the decline of malaria in 20th century Europe, and integrated such data with historical malaria distribution maps in order to quantify changes and differences across the continent before, during and after malaria elimination. Their goal was to provide an understanding as to which factors significantly influence malaria transmission and decline, as well as which factors continue to play a role in limiting the risks of its re-establishment. It was their hope that such knowledge would provide valuable information to countries aiming to rid themselves of the disease or to keep it from a possible return. So what did their analysis reveal?

Of the nine factors analyzed by Zhao et al. as the candidate factors driving malaria elimination, three of them were climate-related (temperature, precipitation and frost day frequency) and each are "often considered to have an effect of malaria transmission," as reported in the scientific literature. However, the three European researchers found that "indicators relating to socio-economic improvements such as wealth, life expectancy and urbanization were strongly correlated with the decline of malaria in Europe, whereas those describing climatic and land use changes showed weaker relationships." Indeed, more often than not, changes in climate tended to run counter to observed trends in malaria, i.e., they should have led to an increased number of cases yet the actual numbers declined.

In considering Zhao et al.'s work, therefore, it would appear that socio-economic and land use factors are more than capable of compensating for unfavorable changes in climate that can lead to malaria transmission and outbreaks. And as long as countries continue to focus on improving these more important elimination factors, malaria trends will continue to remain little influenced by future climate change, model projections notwithstanding.

Posted 22 August 2015