As planet warms, pathogens on the march

Half the world’s population lives in areas with exposure to dengue fever. Parts of the United States may soon join them.

The U.S. Centers for Disease Control and Prevention (CDC) issued a warning to doctors last week about an increased risk of dengue, a mosquito-borne virus most prevalent in tropical climates.
Countries in the Americas have already reported more than 9.7 million cases this year — twice as many as were reported in the region all last year — raising alarm bells about
the prospect for spread in the southern continental United States and increased transmission in places like Puerto Rico.

This notice from the CDC comes in the wake of a recent heat wave that smothered much of the eastern United States. The timing offers a foreboding glimpse
of a future in which climatic change enables diseases to spread into new environments.

“We’re seeing a lot of spread of mosquito-borne viruses, such as dengue, associated with climate change, so none of this is surprising,” said Neil Vora, an epidemiologist and physician at Conservation International. “We are creating
the climatic conditions for these things to happen.”

But how, exactly, are the two related?

On a warming planet, disease vectors like mosquitoes and ticks can thrive in new environments, and disease transmission seasons may become longer as conditions change.
The impact could be profound: A 2019 study, referencing warming based on modeling from the Intergovernmental Panel on Climate Change, projected an additional 2 billion people would face risk of dengue exposure by 2080.

And it won’t just be dengue.

“The thing is, these viruses are going to surprise us time and time again,” Vora said. “Dengue is scary. But what else is out there?”

Last year, for example, Florida and Texas discovered eight cases of locally acquired malaria, the first such cases in the United States in two decades,
leaving physicians perplexed. In parts of South America, including Brazil, scientists are worried about the spread of Oropouche virus,
which had been restricted largely to low-population areas in the Amazon.

Preventing these outbreaks — dengue, Zika, malaria or others — will hinge on reversing climate change. Vora says public health is focused on response rather than prevention, and he delivered a TED Talk last year about how reducing deforestation can help fend off future pandemics.

“Prevention is about going upstream and addressing climate change itself,” Vora said. “We need to walk and chew gum at the same time. In other words, we have to invest in both prevention of diseases, such as through mitigating climate
change through nature-based solutions and phasing out fossil fuels — while, at the same time, investing in response capabilities.
The stakes are too high to keep implementing incomplete solutions.

“The beauty of investing in nature for prevention of disease is that it is inherently equitable. Everyone benefits everywhere, particularly people in the most resource-limited settings. And these measures are agnostic to the pathogen. When you mitigate
climate change, threats downstream get mitigated, too.”

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Max Marcovitch is a staff writer at Conservation International. Want to read more stories like this? Sign up for email updates. Also, please consider supporting our critical work