Slowdown in Global Warming Brought Down Malaria Transmission in Ethiopia

A new study reports that the deceleration in global warming observed toward the end of the past century resulted in a fall in malaria transmission in the Ethiopian highlands.

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The study was led by the Barcelona Institute for Global Health (ISGlobal), an institution supported by “la Caixa” Foundation, and the University of Chicago. The findings have been reported in the Nature Communications journal and highlight the close link between climate and health.

A heated debate on the effect of global warming on malaria incidence has been ongoing for several decades. Researchers consider that the largest effect could be in the highlands, where lower temperatures restrict vector abundance, resulting in seasonal and intermittent outbreaks of the disease.

We see that malaria epidemiology in these areas is strongly under climate control at all scales (months, years and even decades), which settles once and for all the debate on whether climate change is affecting or not the dynamics of malaria in Africa.

Xavier Rodó, Study First Author and Head of the Climate and Health Programme, ISGlobal

During the end of the 20th century and the beginning of the 21st century, there was an evident fall in malaria incidence in East Africa. This decrease could just be the result of disease control measures, or could be due to the temporary deceleration in the increase in global mean surface temperature—a phenomenon observed between 1998 and 2005.

To find a solution to this puzzle, Rodó and his collaborators focused on the Oromia region in Ethiopia, which is a densely populated highland located between 1,600 and 2,500 m above sea level.

This region exhibits the benefit of including complete records of annual cases of malaria due to both Plasmodium falciparum and Plasmodium vivax parasites from 1968 to 2007, and that public health interventions to curb the disease were not reinforced in the region until 2004.

This enables the effect of climate to be separated from that of disease control measures for two parasites known to respond differently to climate.

The researchers used mathematical modeling to analyze the link between malaria cases, regional climate (rainfall and local temperatures) and global climate (specifically the effect of El Niño and the Pacific Decadal Oscillation on the Pacific Ocean).

The findings indicate that the change in malaria cases corresponds very well with variations in regional temperatures: the regional fall in temperatures associated with the deceleration in climate change coincided with the decrease in malaria cases from 2000—five years before disease control measures were reinforced.

This decrease in cases matched with the deceleration in the global surface temperature increase, caused by the El Niño and the Pacific Decadal Oscillation. The analysis indicates there has been a 'chain of effects' from global climate variability to regional temperature variations in East Africa, translating into new cases of malaria in the Ethiopian highlands.

The coupling between disease dynamics and climate conditions is so strong that it is evident at multiple temporal scales, from seasonality to multiannual cycles to decadal trends. Malaria incidence not only tracked changes in temperature, which we had demonstrated before, but also in the decrease at the turn of the century, the focus of this work.

Mercedes Pascual, Study Last Author and Researcher, University of Chicago

According to Rodó, “the evidence that the slowdown in warming influenced malaria transmission demonstrates the strong coupling between disease and climate.” These findings also reiterate the significance of taking climate conditions into account while assessing public health interventions targeted at disease control, and of combining them into early warning systems.

Journal Reference:

Troyan, I. A., et al. (2021) Anomalous High‐Temperature Superconductivity in YH6. Advanced Materials. doi.org/10.1002/adma.202006832.

Source: https://www.isglobal.org/en

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