Dengue fever, an illness that can be life-threatening and is transmitted by mosquitoes, is on the rise throughout the Americas, with record-breaking infection rates.

The dramatic surge in cases is primarily attributed to the rising global temperatures driven by greenhouse gas emissions, as highlighted by recent research.

A study presented at the American Society for Tropical Medicine and Hygiene annual meeting in New Orleans indicates that nearly 20% of dengue cases in the Americas and Southeast Asia have been influenced by climate change, conducted by researchers from the University of Maryland, Harvard University, and Stanford University.

According to the latest information from the Pan-American Health Organization, from January to October 2024, there have been almost 7,500 fatalities and over 12.3 million dengue cases—three times the count recorded in 2023, which was already unprecedented.

“This is truly the worst year for dengue in history,” stated Dr. Gabriela Paz-Bailey, who leads the CDC’s dengue division in Puerto Rico. “Globally, dengue cases are increasing alarmingly.”

The startling rise in infections has raised alarms in the United States, especially in Puerto Rico. Officials estimate that hospitalizations account for about 50% of cases, according to Dr. Paz-Bailey. This year, the U.S. has reported nearly 7,300 dengue cases, a substantial increase from 1,462 in 2023. Puerto Rico has declared a public health emergency in response, maintaining this status throughout the year.

Though the continental U.S. hasn’t experienced a high infection rate compared to the early 2010s, there are growing concerns regarding future risks due to climate change.

While many dengue patients do not exhibit symptoms, those who do may suffer from high fever, body pain, nausea, and rashes. Severe cases can lead to hospitalization or even death.

In severe instances—typically affecting about 5% of infected individuals—patients may experience internal bleeding or shock. Infants, the elderly, and pregnant women are particularly vulnerable to severe dengue.

There are four types of dengue viruses. Infection with one type offers only limited immunity to others, leading to outbreaks as populations encounter different strains. Recurring infections can lead to more severe manifestations of the disease.

Impact of Climate Change on Increasing Dengue Cases

The recent study from Maryland, Harvard, and Stanford did not factor in the spike during 2024 but illustrated that climate change has been a significant driver for the spread of dengue as temperatures rise.

It was determined that climate change contributed to 19% of dengue infections in the Americas and parts of Southeast Asia. Infection rates were notably higher in areas once considered too cool for the Aedes aegypti mosquito, the primary carrier of dengue alongside other illnesses.

By 2050, researchers predict climate change may increase dengue cases by 40% to 57% compared to current levels. In cooler urban settings in Bolivia, Peru, Mexico, Brazil, and Colombia, where temperatures are expected to rise, the disease could potentially impact more than 257 million individuals.

“This signals the need for proactive pandemic readiness, particularly in regions susceptible to dengue spikes linked to climate change,” noted Mallory Jessica Harris, a postdoc researcher at the University of Maryland Institute for Health Computing and co-author of the study. “In recent years, massive dengue epidemics have occurred repeatedly.”

Future forecasts were shared based on analyses of 21 countries, utilizing an average of 11 years of data from each. However, the study did not encompass regions like sub-Saharan Africa or South Asia, both affected by dengue spread. It also omitted data from the continental United States.

The research indicated that temperatures around 82 degrees Fahrenheit are ideal for the mosquitoes that transmit dengue. Some areas are projected to rise above that temperature range, making it difficult for infected mosquitoes and other susceptible creatures to survive. Alarmingly, many regions in the Americas are set to reach temperatures optimum for dengue generation over the next decades, with substantial increases in infection rates expected—between 150% and 200%—in previously cooler areas where ideal temperatures for dengue transmission are predicted.

This includes several cities in the region, such as Lima, Peru, which has reported unprecedented rises in dengue cases this year. The U.S. State Department has issued health advisories regarding dengue outbreaks in Lima. Cases typically escalate during the Southern Hemisphere’s summer, when it is wintertime in North America.

Warmer winters in the southern regions allow infected mosquitoes to survive over seasons that would typically eliminate them.

Urbanization and Poverty: Key Factors in the Increase of Dengue

Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine, explains that climate change is not the sole reason for the ongoing rise of dengue cases.

Urban growth, forest clearance, and economic hardship also play significant roles in creating optimal conditions for mosquito populations that carry the virus, Hotez noted. This trend may extend to parts of the United States, particularly in rapidly developing regions in the Sun Belt.

“We can’t overlook the potential for arboviruses, especially dengue, to become common in the southern U.S.,” Hotez warned, mentioning states like Texas, Florida, and others along the Gulf Coast.

Poverty-stricken communities often lack air conditioning and adequate screens on windows and doors, making it easier for mosquitoes to enter homes. Additionally, insufficient sanitation can lead to the accumulation of standing water, a breeding ground for mosquitoes that can transmit the virus to residents.

Paz-Bailey from the CDC pointed out that the resurgence of travel following the COVID-19 pandemic has also played a crucial role in the sharp rise of dengue cases in the U.S. This issue could escalate in the coming years. If a person infected with the virus enters the country, a local mosquito could bite them, get infected, and then pass the virus to others nearby.

As temperatures rise across much of the U.S., it could facilitate ongoing local transmission, which has already been observed in California and Florida.

Severe weather events like hurricanes can further support mosquito populations by creating standing water in their aftermath, thus promoting suitable habitats for these pests.

Vaccine Development and the Possibility of Modified Mosquitoes

To curb the spread of dengue, several strategies can be employed. One effective approach highlighted in studies is the reduction of greenhouse gas emissions that escalate temperatures.

While vaccines exist, they are not widely accessible. The remaining doses of Dengvaxia, the only vaccine approved by the U.S. Food and Drug Administration in 2019, are expected to run out by 2026, and Sanofi, the manufacturer, plans to halt production in 2025.

Improved identification of disease-carrying mosquito species can help prevent outbreaks before they start. However, eliminating mosquito breeding sites can be quite challenging, as even small amounts of stagnant water, such as what can be found in a bottle cap, are enough for them to reproduce.

Researchers are exploring ways to genetically engineer mosquitoes to stop the spread of dengue. A recent study from the World Mosquito Program highlighted that infecting mosquitoes with Wolbachia bacteria has significantly reduced dengue transmission in Niterói, Brazil. However, scientists recognize that such prevention measures require years to establish stable and safer mosquito populations.

Kristie Ebi, a professor at the University of Washington’s Center for Health and the Global Environment, emphasized the importance of historical knowledge for managing current and future outbreaks. The CDC was established nearly 80 years ago to combat mosquito-borne diseases, successfully addressing malaria and yellow fever.

Ebi stressed the need for enhanced preparedness, noting that “climate change is already causing suffering and death today.”

Individuals can protect themselves from dengue by avoiding mosquito bites. Taking precautions like wearing long-sleeved clothing and using insect repellent can help.