Dengue fever is — unfortunately — having a banner year. Can it be quelled?

In the Americas alone, almost 10.4 million suspected cases of dengue, a mosquito-borne viral disease, were reported to the World Health Organization in 2024 as of the first week of July, an increase of 232% compared with the same period the year before.

Peru is a case in point. When torrential rains started to fall there in 2023, a record-breaking dengue epidemic exploded shortly afterward. The case count is estimated at well over 100,000 so far this year.

And dengue isn't just stalking the Americas.

Bangladesh, Burkina Faso, Chad, Nepal, Sri Lanka and Vietnam are among the countries now registering uncharacteristically high numbers of cases of the disease. Many are struggling to get epidemics under control.

More common in the hot and humid climates favored by the mosquitoes that spread it, dengue has evolved from a seasonal nuisance limited to tropical and subtropical countries to a severe year-round public health-care problem worldwide.

And it’s a shocking new disease to deal with in places previously unaffected.

In 2022, Niger’s Abalak Department reported its first-ever case of dengue. In June, Iran reported its first two instances of locally transmitted dengue.

Even hot-weather states in the U.S., such as Texas, Florida and California, have recorded a smattering of locally transmitted cases, while Puerto Rico declared a dengue epidemic on March 25 after reporting at least 549 cases in the first three months of the year.

In late June, the Centers for Disease Control and Prevention issued a dengue alert, urging public health authorities to be aware of "an increased risk of dengue virus infections in the United States in 2024."

What's responsible for this surge? And is there a way to quell dengue? And you may also wonder — if you're not living in an area with an outbreak — what exactly is dengue fever?

How dengue makes you feel

Most cases of dengue are mild and cause symptoms like fever, rash and muscle and joint pain. But when left untreated it can lead to persistent vomiting, bleeding from the gums and nose, difficulty breathing and death. Children are most at risk, especially those under age 5.

Because some patients feel as if their bones are breaking, the virus has an ominous nickname: “breakbone fever.”

Climate change, urbanization and migration have all contributed to the increased spread of the disease, with the mosquitoes that spread it finding new hospitable territory. Increased population density contributes to both more breeding grounds and a bigger vulnerable population. Dengue now persists at a consistent level with predictable rates of infection and spread in two-thirds of the world’s countries.

Lessons in control

Now, authorities and experts are searching for new solutions to quell the disease. And they agree that the best place to start is in countries that have already been dealing with dengue for decades.

While some of those countries are currently struggling to contain their own epidemics, their experience with the disease has helped them cap the number of severe cases and deaths this year. These lessons can provide valuable insights for countries that are newly encountering dengue outbreaks.

Countries across Asia — including Malaysia, Singapore, Sri Lanka and Thailand — have all learned the importance of spreading awareness about how to prevent the spread of dengue.

Neelika Malavige, a professor of immunology and molecular medicine at the University of Sri Jayewardenepura in Sri Lanka, says countries that have lower mortality rates “have many community engagement programs to clean up the environment, reduce mosquito breeding places and educate the public about when to see a doctor.”

In the first six months of 2022, 36,000 cases of dengue fever were reported in Sri Lanka across 12 high-risk districts, the same number registered in all of 2021. So WHO Sri Lanka and the country’s Ministry of Health launched a community engagement program to get the word out about how to eliminate breeding sites for Aedes aegypti mosquitoes — anyplace where water collects, from flower pots to buckets to abandoned tires. The program led to a nearly 60% decline in hospital admissions for dengue fever in those communities and likely prevented major outbreaks that would have required national-scale interventions.

Malavige says that health-care professionals in countries familiar with battling dengue are specifically trained to spot symptoms and complications early, and early intervention with fluid replacement treatment and management — either oral or intravenous — is what keeps cases mild and people alive. “They have managed to significantly reduce case fatality rates and the proportion of patients developing severe dengue and associated complications,” she says.

Leo Braack, a senior specialist of vector control at the Malaria Consortium currently in Thailand and previously based in South Africa, agrees with Malavige about the importance of educating both communities and health-care professionals. But he worries that many countries across Africa — such as Burkina Faso, which has been dealing with dengue for decades but still registered 356 deaths from the disease in just one month last year — aren’t prepared because of a lack of resources.

In a piece Braack wrote for the Malaria Consortium last year, he cited resource constraints, misdiagnosis and misclassification of infections as major challenges in Africa. In addition, the “overwhelming prevalence of malaria south of the Sahara can mask the presence of other arthropod-borne infections, such as dengue, because of the similarity in many of the symptoms.”

Yet there is a lot to learn from Africa — the ancestral home of viruses such as dengue, chikungunya, Zika and yellow fever, as well as the Aedes aegypti mosquito (the primary means of transmission). This history puts the continent in a unique position to help the rest of the world better understand these diseases.

“There is much that the global community can learn from Africa about the original ecology of these viruses and vectors,” says Braack. “Humans in Africa have co-existed with these viruses for many centuries and may have resulted in population-level genetic or immune responses that need better understanding. Africa offers that opportunity.”

The dengue forecast

In the meantime, experts know that the effects of climate change, urbanization and migration won’t soon dissipate. Dengue will continue to spread at a higher rate than ever before, and countries must prepare.

“The focus of health-care services has to be the reduction of severity, complications and deaths,” says Brazil-based André Siqueira, head of the Dengue Global Programme at the Drugs for Neglected Diseases Initiative (DNDi). “This is done with a health-care system that sees patients quickly, classifies them based on degree of severity and carries out the necessary intervention, whether that be oral hydration or by way of IV.”

Brazil’s Federal District, he says, struggled with one of the country’s most deadly epidemics this year and last because of a lack of preparedness by the public health-care system. Home to just 1.39% of the country’s population, the Federal District saw 10% of the deaths (235) caused by dengue in the first three months of 2024, 12 times more than what it registered in all of 2023.

Rio de Janeiro, on the other hand, has become adept at dealing with the disease, with strong public education and mobilization programs. Making up 7.91% of the country’s population, it registered just 63 deaths caused by dengue in those same months.

Rio is also expanding participation in the World Mosquito Program's Wolbachia program — breeding Aedes aegypti mosquitoes that carry the Wolbachia bacteria, which reduces their ability to transmit viruses like dengue. By releasing these mosquitoes, the risk of infection is decreased.

Malavige notes that it’s the high number of cases in the most recent epidemics around the world — many of them record-breaking — that make care much more challenging in many countries and impossible in others.

“It is simply not possible to carry out personalized fluid management with very high numbers of patients,” she says. “We need to invest in long-lasting solutions to find better diagnostics, a treatment for dengue, safer and more effective vaccines and better vector control methods.”

She cites Singapore as having well-organized mosquito control programs and notes that more focus on this type of prevention is needed.

Vaccines are being explored as well. Japan’s two-dose dengue vaccine Qdenga has been rolled out and Brazil’s Butantan Institute is developing its own, but the quantities so far are too small to make a dent in the problem. Dengue vaccines also have a controversial past, since the 2016 deaths of at least 10 children in the Philippines were blamed on a previous iteration of the vaccine.

While Siqueira agrees that the new methods seem promising, he reiterates that the challenges are long term and that many people will become sick before these types of mitigating measures can have an important global impact.

“We can’t take our focus away from adequate management of cases of dengue and the treatment of the disease,” Siqueira says, “if we want to keep people alive.”

Jill Langlois is an independent journalist based in São Paulo, Brazil. She has been freelancing from the largest city in the western hemisphere since 2010, writing and reporting for publications like National Geographic, The New York Times, The Guardian and Time. Her work focuses on human rights, the environment and the impact of socioeconomic issues on people's lives.