Higher temperatures owing to climate change are causing an increase in dengue infections across Asia and the Americas, a new study has revealed.
The study, published in Proceedings of the National Academy of Sciences, stated that climate change was responsible for approximately 18 per cent cases across 21 countries in Asia and the Americas between 1995 and 2014.
Dengue, caused by the Aedes aegypti mosquito, is a fever-inducing mosquito-borne disease with flu-like symptoms. It can turn fatal, with bleeding and organ failure.
Earlier studies have pointed out that rising temperatures and erratic rainfall patterns would result in expansion of Aedes aegypti habitats to non-endemic areas.
The studies projected a 25 per cent increase in dengue spread by 2050, especially in Southeast Asia, sub-Saharan Africa, and parts of South America.
However, it is the first time that scientists have provided direct evidence of a warming climate contributing to increasing the disease’s toll.
These cases translate to over 4.6 million additional dengue incidences annually, the scientists said. They added that these numbers were conservative as they do not include regions where infections are sporadic or poorly reported.
The scientists also did not include large endemic areas, including India or Africa, where detailed data is lacking or publicly unavailable.
The research warns that dengue cases could spike by another 49 per cent to 76 per cent by mid-century, depending on different climate warming scenarios and greenhouse gas emission levels.
“At the higher end of the projections, incidence of dengue would more than double in many cooler locations, including areas in the study countries that are already home to over 260 million people,” the researchers said.
The study said analysis of the data from 21 countries demonstrated that dengue fever cases rise as temperatures increase.
The researchers pointed out that warming weather across the globe due to climate change is reshaping the dynamics of human health.
“The effects of temperature were much larger than I expected. Even small shifts in temperature can have a big impact for dengue transmission, and we’re already seeing the fingerprint of climate warming,” Marissa Childs, lead author and assistant professor of environmental health at the University of Washington said in the statement.
The paper included analysis of more than 1.4 million observations of local dengue cases from 21 countries across Central and South America and Southeast and South Asia documenting epidemic spikes and background levels of infection.
“Dengue thrives in a “Goldilocks zone” of temperatures — incidence peaks at about 27.8 C (82 F), rising sharply as cooler regions warm but dropping slightly when already-hot areas exceed the optimal range,” the findings noted.
With increasing temperatures in cooler and high populations regions such as Mexico, Peru, and Brazil, the cases are expected to rise.
By contrast, a few of the hottest lowland areas may see slight declines. Still, the net global effect is a steep rise in disease, the study said.
The scientists estimated that dengue cases would more than double in many cooler regions including the 21 studied countries that house 260 million people.
They noted that recently reported local cases from California, Texas, Hawaii, Florida, and in Europe indicate an expanding range of dengue. Moreover, urbanisation, human migration and evolution of the dengue virus would further exacerbate the risks.
But medical advances are expected to limit the intensity, making projections a challenge, the researchers said. The study added that aggressive climate mitigation, along with better control over mosquito populations and strengthening of health systems with new dengue vaccines, are key to minimising the disease burden.
“Climate change is not just affecting the weather — it has cascading consequences for human health, including fuelling disease transmission by mosquitoes,” said Erin Mordecai, senior author and professor of biology in the Stanford School of Humanities and Sciences.