Dengue fever: what you need to know about viruses and symptoms
Cases of dengue in the US tend to occur among travelers returning from places like the Caribbean who bring the disease back to local mosquito populations.
Dengue fever, a potentially deadly virus spread by mosquitoes, is spreading across America and breaking records with skyrocketing infections.
The number of cases has increased in large part due to rising global temperatures due to greenhouse gas emissions, new research shows.
Nearly a fifth of dengue infections in America and Southeast Asia were caused by climate change, according to a study that researchers from the University of Maryland, Harvard University and Stanford University presented Saturday at the annual meeting of the American Society for Tropical Medicine and Hygiene in New York. Orleans.
The latest data from the Pan-American Health Organization shows that there were nearly 7,500 deaths and more than 12.3 million infections in the first 10 months of 2024 – three times the number of cases in 2023, which was a record at the time. to write. time.
“Dengue is truly having its biggest year in history,” said Dr. Gabriela Paz-Bailey, chief of the dengue division at the U.S. Centers for Disease Control and Prevention, based in Puerto Rico. “Around the world, cases of dengue have been rising at an alarming rate.”
The sharp increase has raised concerns in the U.S., especially in Puerto Rico, where officials estimate that up to 50% of infections have led to hospitalizations, Paz-Bailey said. The U.S. has recorded nearly 7,300 infections this year, up from 1,462 in 2023. Most of these cases occurred in Puerto Rico, which declared a public health emergency this spring and remains under emergency status.
The continental US has not seen a high infection rate compared to early 2010. But officials are concerned about the predictions in a warming climate.
Most people who get dengue don’t show any symptoms, but those who do sometimes develop high fever, body aches, nausea and rashes. Some infections lead to hospitalization or death.
In severe cases – usually about 1 in 20 infected people – people bleed internally or from their nose or mouth and go into shock. Infants, the elderly and pregnant women are at greatest risk for serious forms of illness.
There are four dengue viruses. A person infected with one of these viruses may have limited immunity to some of these viruses. Populations are sometimes exposed to different species, causing outbreaks to reemerge. Repeated infections can cause severe dengue fever.
Climate change is already responsible for record increases in dengue
The new study from Maryland, Harvard and Stanford did not include the 2024 benchmark peak. But it found that climate change had promoted the spread of dengue as temperatures rose.
Climate change caused 19% of dengue infections in North and South America and parts of Southeast Asia, the study found. Infection rates were significantly higher in regions previously considered too cold to support the Aedes egypti mosquito, which can transmit dengue and other diseases.
By 2050, climate change could cause cases to increase by 40% to 57% over current levels. In cooler urban areas in Bolivia, Peru, Mexico, Brazil and Colombia, where the climate is expected to lead to higher temperatures, researchers found that dengue would affect more than 257 million people.
“This suggests that we need to think about pandemic preparedness, especially in those parts of the world that are vulnerable to increases in dengue due to climate change,” said Mallory Jessica Harris, co-author of the study and postdoctoral researcher at the Institute for health computing from the University of Maryland. “Even in recent years, we have repeatedly seen these very large dengue epidemics.”
Researchers also shared future predictions based on analyzes of 21 countries, using an average of 11 years of data for each country. The study did not include sub-Saharan Africa or southern Asia, two areas also affected by dengue transmission. It also did not include data from the continental US
The study found that temperatures around 82 degrees Fahrenheit are most suitable for the mosquitoes that can transmit dengue. Some regions outside that range are expected to warm, making it harder for infected mosquitoes or other creatures to survive. Unfortunately, the research shows that large parts of America will instead reach optimal temperatures in the coming decades. In previously cooler areas, where temperatures are expected to rise to temperatures ideal for dengue transmission, infections could increase by 150 to 200%.
This includes several cities in the Americas, such as Lima, Peru, which saw an unprecedented rise in dengue infections in 2024. This year, the U.S. Department of State issued a health warning about dengue transmission in Lima. Cases typically increase during the summer months in the Southern Hemisphere, while it is winter in North America.
During the warmer winters in the southern region, infected mosquitoes can endure seasons that would typically kill off their populations.
Urbanization and poverty also play a role in the rise of dengue
Climate change is not the only factor explaining the continued rise in dengue, said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.
Urbanization, deforestation and poverty also contribute to creating environments suitable for infected mosquitoes, Hotez said. This phenomenon could impact the US, including fast-growing areas in the Sun Belt.
“We should not discount the likelihood that arboviruses, especially dengue, occur regularly in the southern part of the US,” Hotez said, citing Texas, Florida and other states along the Gulf Coast.
People living in poverty often lack air conditioning and window or door screens to cool people indoors and prevent mosquitoes from entering. They also lack efficient sanitation to remove standing water where mosquitoes can grow and infect people nearby.
The CDC’s Paz-Bailey said the return of travel after the COVID-19 pandemic has also contributed to a record increase in dengue transmissions in the US. But that could worsen in the future. After an infected person enters the U.S., a local mosquito can bite that person, contract the virus, and then spread it to other people nearby.
Warming conditions across much of the US would then maintain continued local spread, which has already happened in California and Florida.
Extreme weather, such as hurricanes, can preserve mosquito habitats. A storm’s wake can cause standing water to form, creating a thriving environment for mosquitoes.
Vaccines are lacking, but there is promise in adapting mosquitoes
There are steps we can take to reduce transmission. One of the points that emerges from the research is reducing greenhouse gas emissions, which cause temperatures to rise.
Vaccines can also help, but none are readily available. The US has limited access and the last remaining doses of the Dengvaxia vaccine, approved by the US Food and Drug Administration in 2019, are expected to expire in 2026. Sanofi, the company that makes it, plans to stop vaccine production in 2025.
Better detection of disease-carrying mosquitoes can help prevent outbreaks before they occur. However, it is extremely difficult to reduce the environment in which mosquitoes breed because they only need a cap of standing water to hatch their eggs.
Researchers have instead tried to engineer mosquitoes to prevent the spread of dengue. Infecting mosquitoes with Wolbachia bacteria has dramatically reduced dengue, according to a study recently shared by researchers from the World Mosquito Program based on results from the Brazilian city of Niterói, near Rio de Janeiro. But researchers acknowledged that it takes years for prevention programs like these to be effective in maintaining safer mosquito populations.
Kristie Ebi, a professor at the University of Washington’s Center for Health and the Global Environment, said the historical context is useful in helping us prepare for current and expected spread. The CDC was founded nearly 80 years ago to prevent mosquito-borne diseases, and the organization proved successful in tackling malaria and yellow fever.
Better preparation is imperative, Ebi said, because “climate change is causing people to suffer and die today.”
People can prevent the disease by protecting themselves from mosquito bites. This includes covering your arms and legs with protective, loose-fitting clothing and spraying insect repellent.