Many people in the continental United States don’t know much about dengue fever. But that may change in the face of record-breaking surges in cases around the world, driven in part by warmer and wetter weather this year.
With only half of 2024 left, public health officials at the U.S. Centers for Disease Control and Prevention are reminding health professionals and the public to stay on top of a painful — and sometimes debilitating and even fatal — infection spread through mosquito bites Come arm yourself.
According to the World Health Organization (WHO), as of mid-June 2024, nearly 9.4 million dengue cases were reported in the Americas. That's more than double the number of cases reported in all of 2023. The condition is also seen in U.S. travelers returning from areas where dengue-infected mosquitoes are common.
To complicate matters, dengue infection can present with a range of symptoms—from fever, severe pain, and bleeding to no symptoms at all. Often, a second episode of dengue can lead to more severe illness and potentially life-threatening complications, so it's critical to understand prevention, get an accurate diagnosis, and monitor symptom progression.
This echoes the experience of Brunilda Nazario, an Atlanta doctor who frequently travels to Puerto Rico to visit family. Nazario was first infected when he was 11 years old.
“My second round was worse. My bones, especially my spine, hurt so much. Her first symptoms came a few days after returning to Atlanta. In addition to a fever and severe body aches, she She also felt nauseous for several days and noticed bruises on various parts of her body, which ended up sending her to the emergency room for dehydration.
With cases rapidly surging, dengue fever will be high on the list of possible culprits when it comes to dealing with fever-induced illnesses, especially for recent travelers.
Dengue Fever Care in the United States
Dengue fever is a relatively new disease, first discovered in humans in the 1950s.
Although dengue fever is a recent phenomenon, it is the most common infection transmitted to humans through mosquito bites, and nearly 4 billion people (about half of the world's population) live in areas at risk from dengue fever.
The risk of dengue fever is higher in South America, Central America, Mexico, and the Caribbean. South and Southeast Asia and some African countries also have high rates of dengue fever.
This not only creates problems for people living in dengue-endemic areas, but also for travelers who may not show signs of infection until they return home.
“I keep thinking about dengue fever,” said Carlos Salama, an infectious disease physician at Elmhurst Hospital in New York City.
Salama said doctors in the United States, especially those who care for traveling patients, should always consider dengue if they treat someone who has recently traveled to an area of the world where dengue fever exists and is showing symptoms of fever.
“Was it at the top of our list ten years ago? No, it's not. We've seen enough dengue now that we think, 'This is real,'” Salama said.
Salama added that the rise in dengue cases in the United States could also lead to a surge in unnecessary medical costs. He shared the story of an otherwise healthy young woman who recently contracted dengue fever after vacationing in the Caribbean.
“She clearly had dengue fever, and she had millions of dollars of tests done,” Salama said. He suggested that clinicians need to know more about dengue – because there will be more cases – and how to properly assess an individual's risk of developing more severe disease. Clinicians can focus on managing adequate hydration and watching symptoms worsen without unnecessary and often costly testing and consultations, Salama added.
“The challenge we face in the United States is understanding the nature of these tropical diseases,” Salama said.
Anatomy of Dengue Infection
Dengue infection can come from four different types of virus strains and can cause a variety of symptoms. Three-quarters of infections are subclinical, meaning people either have no symptoms or have mild enough symptoms that they don't need to see a doctor.
Of the 25 percent of dengue cases that cause symptoms, most people experience what doctors call a self-limiting illness — their symptoms disappear within three to 10 days.
People with symptoms typically experience fever, severe headache, pain behind the eyes, nausea, vomiting, and muscle, joint, and bone pain. The joint pain can be so severe that dengue fever is sometimes called “broke fever.”
In some cases, people may notice minor bleeding and rash.
About 5-10% of dengue cases progress to a more severe illness, which was once called dengue hemorrhagic fever or dengue shock syndrome because people may suffer severe bleeding or go into shock as a result of the infection.
“Patients get sick very quickly,” said Gredia Huerta-Montanez, a pediatrician and environmental public health leader in Puerto Rico.
The most common risk factors for severe dengue are age (babies are particularly at risk), pregnancy, and chronic diseases such as diabetes, obesity, and heart disease.
But a unique complicating factor also plays a role in severe dengue. Huerta-Montanez noted that the immune response to the first infection sometimes makes a second infection (a different strain of dengue) more dangerous and can increase the risk of serious complications. This risk is known as antibody-dependent enhancement, which is the immune system's response to a second strain of the virus that increases rather than lessens the severity of a subsequent infection.
There are currently no tests or blood markers that can help identify which patients are likely to develop severe illness, but Huerta-Montanez explained that there is a “critical window,” a period lasting about 48 hours after the fever has subsided, that can Provides warning of worsening condition to severe condition.
New abdominal pain, persistent vomiting, accumulation of fluid in the abdomen, liver swelling, and worsening lethargy, combined with certain routine laboratory findings, indicate an emergency situation requiring intensive care and monitoring.
“We have decades of experience dealing with dengue in Puerto Rico,” Huerta-Montanez said. That knowledge, she said, can be shared with clinicians in other parts of the United States.
Dengue fever by the numbers
3-14 days: The incubation period, the time from infection to the onset of symptoms, is usually 4 to 7 days, ranging from 3 to 14 days.
3-10 days: Symptoms may last from 3 to 10 days. Symptoms usually appear suddenly.
2 weeks: Dengue fever is unlikely if fever symptoms occur more than 14 days before travel.
48 hours: The critical stage of dengue fever after the fever has subsided. These 48 hours require vigilance, ensuring adequate hydration, and close observation for the development of warning signs and symptoms.
4 types: There are four different strains of dengue fever. This means a person can be infected with dengue fever up to four times in their lifetime.
second infection: Antibody-dependent enhancement is associated with severe dengue fever, most commonly in second dengue infection. A third or fourth infection is uncommon.
The spread of “human-adapted” mosquitoes
Dengue fever is most commonly spread through the bite of an infected Aedes aegypti mosquito. These mosquitoes feed almost exclusively on humans and do not follow the general dietary patterns of other mosquitoes that feed at dawn and dusk. They will look for blood throughout the day when people are outdoors.
“This is a mosquito adapted to humans,” said Albert Ko, a professor of epidemiology and infectious diseases at the Yale School of Public Health.
Aedes aegypti is also often called the “urban mosquito” because it is so adapted to urban environments. Mosquitoes can lay eggs in standing water found in trash and garbage in urban environments—even a small bottle cap filled with water can lay hundreds of eggs.
Aedes aegypti's current habitat is primarily restricted to tropical and subtropical environments, with some spreading to the southern United States and parts of Europe. Dengue fever may be spread in parts of the continental United States, but most cases occur in travelers returning from dengue-endemic areas. But that may not always be the case.
Warmer, wetter weather caused by climate change may help explain the lengthening of the transmission season in many parts of the world and the spread of Aedes aegypti mosquitoes to higher latitudes and altitudes.
“Previous success in treating dengue fever bodes well for future success,” Ko said.
In other words, Miami, the Florida Keys, Texas border towns and other places that have seen local dengue transmission may be the first places to see more spread in the future.
How to protect yourself from dengue fever
For most people, the key to limiting the risk of dengue infection is to follow CDC guidelines:
- Prevent mosquito bites.
- Use an EPA-approved repellent when traveling to and after returning from dengue-spread areas.
- Wear loose-fitting long-sleeved pants and shirts.
- Control mosquitoes inside and outside your home.
- Use air conditioning and window screens whenever possible to reduce the risk of indoor mosquito bites.
- Tip and empty containers of water to reduce spawning sites in and around your home.
- If you have a fever or symptoms of dengue fever and live in or have been to a dengue-affected area, seek medical attention.
While these steps can reduce our individual risks, Huerta-Montanez said there is still more work to be done at a systemic level. Climate change, deforestation, pollution and urbanization have all been linked to dengue's surge, but the burden is particularly felt by those unable to implement some of these basic strategies.
She explained that Puerto Rican residents have a poorly maintained electrical grid and face frequent power outages, forcing most people to open their windows to balance the risk of heat with the risk of dengue fever.
“All of these factors play into how you prevent and control dengue. Dengue is a neglected tropical disease, but I think it's a disease caused by environmental injustice,” she said.
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