10X Increase In Global Dengue Cases Reported To WHO 2000-2019; 5.2 Cases In 2019

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This year’s dengue outbreaks have not been restricted to Bangladesh. More than 4.5 million cases and 4,000 deaths related to dengue have been reported this year, through the beginning of November, from 80 countries. More than half of those cases were in South America, with epidemics in Brazil, Peru, and Bolivia, but there were also outbreaks in South and Southeast Asian countries, including Sri Lanka, Thailand, and Vietnam.

Dengue infections have been rising in tropical and subtropical regions for the past two decades: Cases reported to the World Health Organization (WHO) increased from about half a million in 2000 to 5.2 million in 2019. Improved diagnostics and reporting explain much of this jump, but a combination of population growth, increasing urbanization and travel, and climatic changes is also boosting Aedes mosquitoes, which drives up transmission in existing hotspots and spreads it toward new areas at both higher latitudes and higher altitudes. In recent years, dengue has popped up in places it had never been seen, including Afghanistan, parts of Southern Europe, and, this year, Chad.

In July, a senior WHO official flagged the role of rising temperatures and humidity levels — in addition to this year’s El Niño — calling the outbreaks a “canary in the coal mine of the climate crisis.” About half the world’s population is already exposed to dengue risk; a 2019 climate modelling study projected that under a moderate warming scenario, an additional 2 billion people would be at risk of dengue exposure by 2080, compared to 2015.

Bangladesh’s crisis is thus “a wake-up call,” especially for South Asia, said Ayesha Mahmud, a health demographer specializing in infectious disease at the University of California, Berkeley. “Understanding the impact of these drivers of dengue transmission will be crucial for forecasting outbreaks in the future,” she added, “particularly in the context of predicted climatic changes, such as increases in mean temperatures across the tropics and the intensification of the monsoon season.” A warming and urbanizing world has been good for A. aegypti, the main vector of the dengue virus. According to the 2020 Lancet Countdown on Health and Climate Change, rising global temperatures between 1950 and 2018 increased the climate suitability for the transmission of the dengue virus by almost 9 percent for A. aegypti and 15 percent for A. albopictus.

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https://e360.yale.edu/features/dengue-fever-climate-change