Climate change linked to global dengue riseExBulletin

A nurse takes care of patients at a hospital near Lima, Peru. The country experienced a dengue outbreak in 2024. This pattern was replicated in many countries around the world. New research suggests climate change may be contributing to the spread of mosquito-borne diseases.

Juan Carlos Cisneros/AFP via Getty Images

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Juan Carlos Cisneros/AFP via Getty Images

By 2023, approximately 6 million dengue fever More than ever were reported around the world. And in 2024, that record was blown away. More than 12 million infections have been reported worldwide so far this year.

However, the number of infected people had been increasing for several years. A new study, currently awaiting peer review, suggests that climate change is likely played an important role in the spread of the disease from 1995 to 2014, according to an analysis presented at the American Society of Tropical Medicine and Hygiene conference in New Orleans in November. During that period, climate change increased the number of infections by about 20% across the 21 countries studied (countries with existing dengue outbreaks, such as Indonesia, India and Brazil).

Erin Mordecai, an infectious disease expert at Stanford University and one of the authors of the new analysis, said that as the climate continues to change, the number of infections will skyrocket even further, surpassing the record numbers of the past few years. He says it's possible.

If the world warms further due to human-induced climate change, she says, “in many parts of the study region, dengue fever rates will more than double as predicted.” But she emphasizes that if global temperatures are contained through climate action, growth can be curtailed – if not stopped, at least minimized.

Dengue fever is the most common tropical disease in the world. In about a quarter of cases, there is a painful fever and a feeling of aching joints and bones, leading to the common name “breakbone fever.” in a few cases And in most cases, catching the disease a second time can be fatal.

Millions of dengue cases occur around the world each year. However, there is currently no vaccine generally available for adults, and there is little other than palliative care to manage the disease once contracted.

Climate signature on dengue fever

Dengue fever is spread between people by two types of mosquitoes. Aedes albopictus and Aedes aegypti.

“Mosquitoes are febrile,” meaning they're cold-blooded, Mordecai explains. “So when the weather gets warmer, everything in your body speeds up.”

Dengue fever is transmitted by two types of mosquitoes. An adult female of one of those species, Aedes albopictus, is examined under a microscope. Each species grows under specific climatic conditions. Climate change is expanding these ideal areas to many new parts of the world, increasing the number of infections.

Kevin Frayer/Getty Images

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Kevin Frayer/Getty Images

Mosquitoes grow quickly. They replicate the virus more effectively in the intestines. As temperatures rise toward ideal levels, they bite more aggressively.

Previous laboratory studies have shown that these mosquito species breed within a predictable temperature range. for Aedes albopictusthe ideal Goldilocks temperature was approximately 79 degrees Fahrenheit. for Aedes aegyptiit was a slightly high but mild 84 degrees.

Mordecai says there are built-in limitations. If temperatures rise too far above Goldilocks temperatures, mosquitoes will begin to suffer and die. And dead mosquitoes cannot spread disease.

Researchers were able to track changes in temperature over time in parallel with changes in reported disease cases. Climate models can then be used to determine how much of each location's temperature increase is due to anthropogenic climate change. This method is called attribution. Then, using advanced statistical techniques borrowed from economics, they were able to link human-induced increases in temperature to the increase in infections.

Similar strategies are now commonly used to diagnose the signatures of anthropogenic climate change in extreme weather events such as heat waves and hurricanes. But the new analysis is one of the first to explicitly link climate change to changes in infectious disease cases.

Marta Choquette, a disease ecologist at Lancaster University in the UK, said: “Understanding how much of the increase in disease is due to climate can help us predict how infectious diseases will respond to future climate change. “I feel more confident,” he said. This will help us make better long-term plans for how to allocate various public health resources. ”

Overall, researchers found that temperature conditions generally favor the spread of the disease, especially in areas such as the Mexican highlands, Bolivia, and Brazil. Similar growth was seen in hotter regions such as Thailand and Cambodia, but only by a small amount because temperatures were already close to the upper limit of mosquito production.

We can also look to the future to see where risks are likely to occur and how many cases are likely to occur in an even more bleak future. In many parts of South America, especially those currently at the cold end of the mosquito's preferred temperature range, the number of mosquito infections could double by mid-century if warming continues on its current trajectory. Only Cambodia was predicted to see a decline in the number of infections.

“Many of the warmer regions are going to have better conditions, and the scary thing is that those regions will… It actually happens to overlap with a city with a high population density.” .

A medical worker uses a sprayer to spray insecticide to kill mosquitoes that spread dengue fever ahead of a Day of the Dead celebration in Merida, Mexico. In 2024, a new record was set for the number of dengue fever cases reported worldwide.

Hugo Borges/AFP via Getty Images

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Hugo Borges/AFP via Getty Images

The study did not include countries where dengue is still rare (including the United States), but cases within U.S. borders have also increased sharply in recent years, including in hot, humid regions such as Florida and southern Texas. There is. However, in 2023, several cases of community-acquired dengue fever were reported. First time in Southern California. More individuals were confirmed in Los Angeles County this year.

Katherine Walter, an epidemiologist at the University of Utah, said high numbers of dengue cases in other parts of the world increase the likelihood that the disease will make its way into new areas, such as the United States.

“The world is more connected than ever, and borders are artificial,” she says. “Unchecked viral infections do not stay in one place.”

Public health efforts remain critical – and many things

Benny Rice, a disease ecologist at Princeton University, says a warming planet is contributing to the spread of the disease, but it's not the only reason. Dengue fever, like other diseases spread by “vectors” such as mosquitoes and ticks, is controlled by a vast number of factors.

Urbanization, especially new unplanned developments on the outskirts of cities around the world, often creates havens for mosquitoes and increases the potential for disease outbreaks. Global travel also allows diseases to spread quickly and easily between regions. Other meteorological factors, such as rainfall frequency and intensity and extreme weather events, also influence the dynamics of dengue outbreaks.

In a way, Rice says, all that complexity represents opportunity. He points out that even if climate change affects 20% or more of dengue cases, 80% of cases could be controlled. “Public health interventions that have existed for many years are more important than ever,” he says. – From proactive efforts to control mosquito populations to building strong local health networks.

Nevertheless, the study shows that “climate really provides context for when and where outbreaks occur,” Campbell said.

This analysis suggests that dengue cases will continue to surge as the global climate continues to warm. The number of infections could increase by 60% by mid-century as more parts of the world enter mosquito-friendly temperatures.

But Mordecai said this points to a clear solution, and that if we succeed in slowing global warming by reducing global warming emissions, alongside other public health measures, we can reduce the risk of is expected to be reduced.