Dengue is on the rise in the US. See how to protect yourself

DEnge is not typically a disease that people in the US worry about. But cases in the U.S. this year are already approaching the total number of cases in all 2023. More than 9.7 million cases have been reported in North and South America, which is double the number of cases reported last year. The global picture is also alarming: The World Health Organization (WHO) reported 6.5 million cases in 2023, a record.

Here’s what you should know about the rise of dengue fever in the US

What is dengue?

The infection can have very different effects, from no symptoms to death. But its nickname is break-bone fever, due to the severe chills that accompany a fever that can reach up to 104°F. Although it is not fatal in most cases, it can be if it progresses to severe dengue fever, in which people develop dangerous bleeding as their blood vessels become compromised and begin to leak, and clotting factors begin to decline.

Why cases are rising

How dengue is transmitted by Aedes mosquito, anything that contributes to the increase in mosquito populations will also fuel the increase in dengue fever (along with other mosquito-borne diseases such as West Nile virus, Zika, and malaria). As of 2023, 43 states in the US have reported cases of West Nile, and so far in 2024, 11 states have done so. Mosquito populations are increasing around the world, thanks to climate change, which is providing warmer climates that mosquitoes favor, as well as heavy rains, which provide the pools of water where the insects lay their eggs. The dengue virus is making the most of these fertile circumstances.

Dr. Gabriela Paz-Bailey, head of the dengue department at the US Centers for Disease Control and Prevention (CDC), says there is another reason for the increase in dengue fever this year. Dengue outbreaks tend to be cyclical, caused by any combination of four main types of virus, known simply as dengue 1, 2, 3 and 4. “People who are infected with one type of dengue are protected for a few years , but the immunity disappears and they are susceptible to contracting another type”, she says. “In 2019, the big epidemic in the Americas was mainly caused by dengue 1 and 2, and now dengue 3 is circulating, so people have less immunity.”

See more information: The scents and colors that mosquitoes are attracted to

How many cases of dengue have been reported in the US?

According to the CDC, more than 2,500 cases have been reported so far this year. Around 800 of them were contracted when people traveled abroad and the rest were transmitted locally. Most U.S. cases occur in Puerto Rico, where high concentrations of mosquitoes have led local health officials to declare dengue fever a public health emergency in March.

Infectious disease experts say most local cases in the continental U.S. likely occur when a mosquito that bit a recently infected traveler transmits the disease to someone else. In the continental US, locally acquired dengue cases have has been reported in Florida.

“The reservoir is already seeded and the mosquito populations [in the continental U.S.] already has [the virus],” says Dr. Robert Murphy, professor of infectious diseases and executive director of the Robert J. Havey, MD Institute for Global Health at Northwestern University. “There is very little to stop this other than being more aware and ready to diagnose cases.”

What is the government doing?

The CDC issued a Health Alert Network Notice on June 25, urging doctors to be alert to rising cases and to test people who report symptoms of fever and chills and who have recently traveled, especially to parts of the world where dengue fever is endemic, such as Puerto Rico, the Virgin Islands from the USA, Micronesia, Marshall Islands and Palau. Identifying infected people can also help limit the spread of the virus if they restrict the time they spend outdoors, when they could be bitten by local mosquitoes that would become additional vectors of the disease.

Paz-Bailey says the blood test is available at public health labs and some commercial labs. For now, “there are no expectations that there will be major outbreaks in the continental United States,” she says. “But there can be small chains of transmission, so we need to do everything we can so doctors can identify dengue early, order the right tests and help everyone protect themselves.”

Is there treatment for dengue fever?

There is no antiviral treatment; care involves lowering fevers and ensuring people stay hydrated. Doctors should closely monitor patients who have other health problems, such as heart disease or diabetes, as infection can make these problems worse. “Dengue is a systemic disease and the virus can affect any part of the body,” says Dr. Sharon Nachman, professor of pediatrics at Stony Brook Children’s Hospital. “There is no part of you that dengue does not touch.”

Although most people recover from the infection after two to seven days, some will develop severe dengue fever and require hospitalization. In these cases, patients continue to vomit, feel extremely tired and lethargic, and develop dangerous hemorrhages that can cause shock. Doctors should watch for these warning signs 24 to 48 hours after the fever disappears.

Is there a dengue vaccine?

There is a vaccine, Dengvaxia, approved in the US, but only for children aged 9 to 16 who have previously had dengue infection and lived in areas where the disease was endemic. The injection involves three doses given six months apart. The vaccine, manufactured by Sanofi, was approved in 2019, but due to the small population it targets, demand has been low. A spokesperson said the company has decided to halt production of the vaccine until 2026 “due to low global demand.”

Other countries around the world have approved vaccines that are recommended by the WHO and can protect against serious disease, but they are not approved in the US. One of them, made by a Japanese manufacturer, is effective against dengue 1 and dengue 2, but not dengue 3, and the company is currently studying its effectiveness against dengue 4, says Paz-Bailey.

See more information: Why You Can Get So Many Diseases From Mosquitoes

If I have had dengue before, do I have immunity?

Yes, in a way. But because there are four types of dengue, people can be infected multiple times and become equally sick if a different version of the virus infects them each time. And the dengue virus has a unique characteristic that makes repeat infections potentially more serious. “Something interesting happens after you get infected for the first time,” says Paz-Bailey. “After the first infection, the antibodies you develop help the virus infect cells during a second infection, which results in more virus production, a higher viral load and a higher risk of severe dengue. Because of the way the immune system behaves, the antibodies you develop after a first infection will not help you during a second infection, but may actually make the infection worse.”

Is there anything I can do to protect myself?

The best advice is to avoid being bitten by a mosquito, as many of them now carry different diseases. Using insect repellent and wearing long sleeves and long pants to cover any exposed skin can protect them from feeding on your blood. And if possible, Paz-Bailey suggests using air conditioning and closing windows to prevent mosquitoes from flying into the house. Getting rid of their breeding sites is also essential. “Inspect your home for standing water and empty, scrub and turn over any containers that could hold water,” she says. “Even a bottle cap and can contains 100 mosquito eggs.”