Cases of the vector-borne illnesses yellow fever and dengue appear to be rising in South America. As the steady overheating of our planet creates ideal conditions for mosquitoes to thrive, disease outbreaks could be exacerbated worldwide. 

What's happening?

As the Guardian reported in November, there have been at least 356 cases of yellow fever and 152 related deaths in South America so far this year. The figures come from the Pan American Health Organization and are among the very worst for the continent since 1960.

The Aedes mosquito species, which can transmit both yellow fever and dengue, thrives in warm conditions and stagnant water. As global temperatures rise and extreme weather events stoke unpredictable rainfall, the mosquitoes' range has increased significantly. Now the insects are spreading not only within tropical and subtropical environments but also pushing into more temperate zones, like those of Europe, according to the news outlet.

"And whether it's bacteria or viruses, they transmit, they're just smarter than humans in that case because they're more adapted, and they will adapt to survive," Maria Guevara of Doctors Without Borders told the Guardian. "We are much too slow. We know what we need to do about climate change, but we're not doing anything."

Indeed, the high adaptability of mosquitoes may only complicate the dangers they bring to new regions.

Why is this a problem?

Diseases like yellow fever and dengue pose significant threats to well-being. 

Both can cause high fevers, severe headaches, muscle pain, and nausea. Globally, over 30,000 deaths may be attributed to yellow fever annually, with the vast majority historically happening in Africa. In 2024, 12,000 deaths were attributed to dengue. Now, disease burdens may be shifting to new regions.

Both illnesses can complicate pregnancies and endanger maternal health. A dengue infection during pregnancy could result in pre-term birth and low birth weight, and, according to the World Health Organization, about half the global population is now at risk of a dengue infection.

These health concerns also jeopardize families' economic security. Even short-term illnesses, but especially those that proliferate within already vulnerable communities, can reduce productivity and earning potential.

Outbreaks also challenge health care systems, particularly when infections are initially asymptomatic. Monitoring, early response, and transmission prevention are key but difficult to keep up with in overburdened and inequitably-resourced settings, where medical professionals are working to balance various emerging needs.

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Meanwhile, our planet's warming trends stand to make the problem even worse in the years ahead, with disproportionate threats facing low- and middle-income countries.

What's being done?

Scientists have been working to develop solutions to the growing mosquito problem and to prevent the spread of disease to humans. For example, one recent effort involves sterilizing mosquito populations to limit their numbers without harmful chemicals. A new spray may also repel mosquitoes and help to curtail disease spread. 

Public health experts, meanwhile, have been helping people to better understand their mosquito-related disease risks and how to address them.

While a mass transition to cleaner energy sources might be the biggest step we could take to help mitigate the underlying causes of higher vector-borne health risks, individuals and communities can also come together to take preventive measures now. Making insect repellent, mosquito nets, window screens, and protective clothing (like long sleeves and pants) more equitably accessible can make a big difference. Infrastructural moves to improve drainage and prevent the build-up of standing water may also help.

And with the potential for infection rates to rise, one of the most meaningful steps may be strengthening funding mechanisms for the distribution of essential medicines, including vaccines that can safely prevent illness and medications that can help to address symptoms.

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