NBC
Meg Norris was traveling in Argentina in April when she suffered the first symptoms of dengue. The weather in Salta, just south of the border with Bolivia, was warm, but Norris, a 33-year-old woman from Boulder, Colorado, wrapped a fleece sweatshirt around her body to keep from shivering.
“I thought it was sun poisoning,” he said.
That night he woke up sweating and spent hours burning and freezing. In the morning her eyes hurt and she had swollen lymph nodes. For the next week she could do nothing but sleep, hydrate, and wait out the body aches that give the disease its nickname “broken bone fever.”
Latin America is experiencing the worst dengue outbreak ever recorded. The number of cases in the first four and a half months of 2024 is already 238% higher than last year at this time, which in turn ended with a record of 4.1 million cases, according to the Pan American Health Organization.
An unusually wet and warm summer season caused by the El Niño weather phenomenon has created ideal conditions for mosquitoes that spread dengue to breed en masse and carry greater quantities of the virus.
Experts warn that this could be a preview of what dengue will be like in the future. The climate crisis is creating unusually benign conditions that are already expanding the range of mosquito-borne diseases.
“This is worrying in places where dengue has not occurred in recent history: North America and Europe,” said Albert Ko, professor of microbial disease epidemiology at the Yale School of Public Health.
Dengue is a viral fever caused by four different viruses and transmitted through mosquito bites. It is common in many tropical regions of the planet, but has begun to appear in more temperate climates. The mosquitoes that transmit dengue fever, Aedes aegypti, are now regularly found in the southern parts of the United States, but recently, the insects have been found as far north as the San Francisco Bay Area and Washington, D.C. A study 2019 predicted that another 2 billion people will be at risk of contracting dengue fever by 2080.
“We are definitely concerned,” Ko said.
Why are dengue cases increasing around the world?
Historically, dengue outbreaks have occurred in the Americas every three to four years, explained Dr. Gabriela Paz-Bailey, chief of the dengue branch in the division of vector-borne diseases at the Centers for Disease Control and Prevention. (CDC, in English). “But now we see them every year,” she said.
This is partly due to the climate crisis.
A warmer climate expands mosquitoes' habitat and allows them to breed year-round, rather than just in the warmer months. Warmer temperatures also cause viruses to reproduce more quickly, which means they end up carrying many more viruses, increasing the likelihood that a person will become infected if bitten.
“We are also seeing dengue cause outbreaks at times when they don't normally occur,” Ko said.
Not only have dengue cases in South America been unusually high this year, but they have also occurred early in the season. Similarly, Puerto Rico, a place where dengue outbreaks can occur in the summer and fall, declared a public health emergency in late March after it was overwhelmed with dengue cases and more than 400 people were hospitalized.
In recent years, the epidemic has spread to areas of southern Brazil and northern Argentina, where dengue had not previously been a big problem, according to Ko. “This gives us an idea of what we can see here in North America in the coming decades,” he said.
How could dengue spread in the US?
Just because Aedes aegypti mosquitoes are found in places outside their normal range doesn't mean they carry the dengue virus, but those first insects are a warning of what may be to come, Ko added.
Locally transmitted dengue infections — meaning the infected person did not become ill abroad — remain rare in the United States, but have recently been observed for the first time in some states. Last October, California health authorities reported the first case of locally transmitted dengue in Pasadena. Local transmission has also occurred in Arizona, Florida, and the south coast of Texas.
Last summer saw unprecedented heat waves in Europe, where cases of local transmission of dengue were observed in France, Italy and Spain.
“I think this means that dengue will become more common,” Paz-Bailey said, adding that the main concern remains the significant increase in cases in places where the virus is already endemic.
She does not expect significant outbreaks of dengue fever in the United States this summer, but the specialist said it is likely that some people will travel to regions where cases are higher than usual and bring the virus back home.
“Travel-associated cases give rise to small chains of outbreaks,” Paz-Bailey insisted.
Humans are reservoirs for dengue, so for widespread transmission to occur, there must be enough infected people for mosquitoes to reliably bite someone with the virus and spread it to someone else.
“That's why we're seeing a dengue outbreak in Puerto Rico right now,” said Michael von Fricken, director of the One Health Center of Excellence at the University of Florida in Gainesville. “They have reached this tipping point where there are enough infected humans that they are subsequently infecting other mosquitoes that continue to transmit the disease,” he added.
Florida has recorded 176 cases of dengue so far this year, the vast majority in people who were infected in other countries, most often Brazil or Cuba. The Florida Department of Health has only recorded seven cases of local transmission of dengue in the state so far this year. In all of 2023, the department documented 173 cases of local transmission, most of them in Miami-Dade County.
What are the symptoms of dengue?
Dengue is caused by four viruses, so a person can be infected four times throughout their life. According to the CDC, only one in four people have symptoms the first time they are infected.
According to Ko, the initial symptoms are usually fever and headaches, fatigue, nausea, vomiting, a measles-like rash, as well as very painful body ailments.
Most people recover within one or two weeks, but about 1 in 20 people develop severe dengue, which can be fatal. The more times a person is infected with dengue, the greater the risk of complications.
“After the first exposure, the risk of suffering from dengue hemorrhagic fever or severe symptoms increases exponentially,” Von Fricken added. Dengue also becomes more deadly with each infection.
Although the United States has a dengue vaccine, it is only approved for children ages 9 to 16 who live in places where dengue is endemic, such as Puerto Rico, American Samoa, or the Virgin Islands.
Additionally, children can only receive the vaccine if they have previously had a dengue infection. This is because if a person gets vaccinated and then gets their first dengue infection, they are still at risk of becoming seriously ill, just as someone gets sicker from their second infection. Since most Americans have not had dengue, “that vaccine is not very helpful” for most, Ko said.
There is no specific drug to treat dengue. Instead, doctors simply treat the symptoms and keep the patient comfortable until the virus runs its course. That means resting and drinking plenty of fluids. Ko said people should try to take acetaminophen (such as Tylenol) for pain and fever if they can, since nonsteroidal anti-inflammatory drugs (NSAIDs), including ibuprofen and aspirin, can worsen bleeding if someone develops dengue hemorrhagic fever. in which your blood vessels are damaged and become leaky.
Paz-Bailey said it is important for people traveling to places with dengue to stay in air-conditioned places when possible, use insect repellent, and wear long sleeves and pants to avoid mosquito bites.
Mosquito nets can be useful, but the mosquitoes that transmit dengue usually bite during the day, so they may be less useful than in preventing other mosquito-borne diseases, such as malaria, Ko explained.
At home, people can make their yards less attractive to mosquitoes by reducing the amount of standing water, especially after a rainy event.
“It is difficult to control the mosquito population, so we have to attack it with everything we have and diversify our strategies,” Paz-Bailey said. “None on its own will be enough.”
