Federal health officials have warned that the risk of contracting dengue fever in the United States has increased this year, a worrying sign as global cases of the mosquito-borne disease have reached record numbers.
In the first half of this year, countries in the Americas reported twice as many cases as in all of 2023, the Centers for Disease Control and Prevention reported Thursday in an alert to providers health care.
The region has recorded nearly 10 million cases of the virus so far in 2024, most of which came from outbreaks in South American countries like Brazil and Argentina.
While local transmission of the virus in the continental United States has been limited, Puerto Rico, which is classified as having “frequent or continuing” dengue risk, declared a public health emergency in March and reported nearly 1,500 cases. .
Cases of dengue fever, a viral disease transmitted by mosquitoes and which can be fatal, are increasing around the world. This increase is occurring both in places that have long struggled with the disease and in areas where its spread was unknown until a year or two ago, including France, Italy and Chad, in central Africa. .
There have even been a few hundred cases of local transmission in the United States. Florida health officials urged the public to take precautions — like wearing insect repellent and throwing away standing water — after reporting a locally acquired case of dengue fever this month.
What is dengue and why is it becoming more and more common?
Dengue fever, a viral fever, is transmitted by Aedes mosquito species. This can cause excruciating joint pain. It is also known by a sinister nickname: fracture fever.
The Aedes aegypti mosquito, the cause of many current epidemics, is native to Africa, where it originally lived in forests and fed on animals. But decades ago, the species spread to the rest of the world via trade routes.
It has adapted to urban areas, feeding on people and breeding in small pieces of water trapped in places such as old tires, discarded bottle caps, and trays used to catch air conditioner drips.
Today, as more people migrate to urban areas — many to poorer housing in developing countries — they are more vulnerable to the virus. And climate change is driving the mosquito to new places, where it thrives.
“Aedes mosquitoes thrive in warm, humid environments, so it is certain that climate change, rising temperatures as well as extreme weather events are helping to expand their habitat,” said Dr. Gabriela Paz-Bailey, head of the dengue branch of the CDC’s National Center for Emerging Markets. and zoonotic infectious diseases.
How dangerous is dengue?
Only one in four cases of dengue is symptomatic. Some infections may cause only a mild flu-like illness. But others can cause terrible symptoms, including headaches, vomiting, high fever and joint pain. Complete recovery may take weeks.
About 5 percent of people who get sick will progress to so-called severe dengue, which causes plasma, the protein-rich liquid component of blood, to leak out of blood vessels. Some patients may go into shock, causing organ failure.
Severe dengue has a mortality rate of up to 5 percent in people whose symptoms are treated. However, without treatment, the mortality rate is 15 percent.
Severe dengue may not be treated because patients live far from medical care or cannot afford it. This can happen because hospitals are overwhelmed with cases during an outbreak or because dengue is not diagnosed in time when it appears in a new area.
Who is at risk?
Already 40 percent of the world’s population lives in areas where they are at risk of dengue infection; the disease is more common in tropical countries, such as Brazil.
The people most vulnerable to dengue live in housing that does not keep them away from mosquitoes. In studies of communities along the southern border of the United States, in areas where the Aedes aegypti mosquito is well established, researchers found that there were as many, or sometimes more, mosquitoes on the side from Texas, but much fewer cases of dengue than on the Mexican side. .
That’s because more people on the U.S. side of the border had screened windows and air conditioners, which limited their exposure to mosquitoes, and lived farther apart and were less sociable.
By visiting friends and relatives less, residents were less likely to spread the virus to new areas where a mosquito could contract and transmit it.
Dengue fever is unlikely to become a serious problem in the United States, “as long as people continue to live the way they live now,” said Thomas W. Scott, a dengue epidemiologist and professor emeritus at the University of California. in Davis.
Outside of Puerto Rico, most dengue cases in the United States result from travel to countries where the virus is endemic. But scientists say dengue will continue to spread to places that have never been affected before.
Besides climate change, increasing rates of urbanization around the world also play a role, said Alex Perkins, an associate professor of biological sciences at the University of Notre Dame and an expert in mathematical modeling of dengue transmission.
If people have recently arrived from rural areas, they are unlikely to have priority immunity, so the virus can spread quickly through the population.
“I think the general expectation that this problem is going to become a growing problem in the United States is reasonable,” he said.
Dr Perkins said the experience in southern China provides a cautionary tale. Historically, the region has recorded only a handful of dengue cases each year. Then, in 2014, there were 42,000 cases in Guangdong province.
“All of a sudden, within a year, the number increased by several orders of magnitude without any real warning,” he said.
“In endemic settings, we continue to have record years, year after year, and that’s what’s driving all of these imported cases in the United States and elsewhere,” he added.
“And when it comes to the most marginal transmission settings, like the southern United States, southern Europe and China, the situation is not improving either. So it’s not really improving anywhere: everything is bad.
Is there a treatment for dengue fever?
There is no treatment for dengue fever. Patients’ symptoms are managed with medications, such as those needed to control pain. But pharmaceutical companies have antivirals in clinical trials.
Is there a vaccine?
The search for a dengue vaccine has been long and complicated.
Dengvaxia, a vaccine developed by French company Sanofi, was widely rolled out in countries including the Philippines and Brazil in 2015. But two years later, the company said vaccinated people who contracted the virus were experiencing more severe cases.
The CDC recommends the use of Dengvaxia only in endemic areas for patients with prior laboratory-confirmed dengue infection.
The World Health Organization recently recommended a new vaccine, called QDENGA, which can be used regardless of previous infection status, for children aged 6 to 16 living in areas with high dengue transmission .
The vaccine has already been introduced in Indonesia, Brazil, Thailand and 16 European countries, including Britain and Italy. But it won’t be available in the United States anytime soon.
What else can we do?
Some countries have acted aggressively against dengue and are managing to control it. Singapore, for example, uses a combination of methods, including inspecting homes and construction sites in breeding areas, with steep fines for violating the rules.
“It’s a successful approach, but they have a very large budget to support these activities,” Dr. Paz-Bailey said. “But not all countries have this.”
Brazil and Colombia have successfully deployed a bacteria called Wolbachia. When Aedes aegypti mosquitoes are infected with the bacteria, they can no longer transmit the dengue virus.
Researchers in South America are mass producing mosquitoes infected with Wolbachia and releasing them to breed with wild insects to spread the bacteria within the mosquito population.