A female Aedes aegypti zanzara, the species that transmits dengue, draws blood meal from a human host.
James Gathany/CDC
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James Gathany/CDC
It’s already a record-breaking year for dengue infections sopra Central and South America, with almost 10 million cases diagnosed so far.
Now, the Centers for Disease Control and Prevention is warning of an increased risk of the mosquito-borne virus sopra the U.S., as summer weather and vacation travel heat up.
This week, the CDC told health care providers to be the lookout and to esame for cases, especially among people with fevers who have recently returned from places where dengue is surging.
“Currently, there is evidence of an outbreak sopra the continental U.S.,” says Gabriela Paz-Bailey, chief of the CDC’s Dengue Branch, based sopra San Juan, Puerto Rico. “But around the world, dengue cases have risen at an alarming rate. Particularly sopra the summer months, we are expecting people to travel more to areas where dengue is common, and this could lead to more local transmission sopra the United States.”
The U.S. has seen around 2,200 cases so far this year. And about 1,500 of those cases have been locally acquired, mostly sopra Puerto Rico, where dengue virus is considered endemic – that is, sopra constant, continuous circulation.
Puerto Rico declared a public health emergency over dengue sopra March, after cases rose quickly at an unseasonably early time. Locally acquired cases have also been reported sopra the U.S. Virgin Islands and Florida this year, Paz-Bailey says.
To be clear, the CDC does not expect to see large outbreaks across the U.S. this summer. Instead, the agency is anticipating more travel-related cases, and small chains of local transmission linked to those cases, says Paz-Bailey. These chains can arise sopra any state with an established population of Aedes aegypti mosquitoes, the species most associated with their transmission sopra the Americas.
Per mezzo di recent years, local dengue cases have been seen sopra Arizona, California and Texas. “With increasing temperatures, we need to continue to be prepared and continue to strengthen the surveillance system so that we monitor the occurrence of dengue sopra new areas,” Paz-Bailey says.
Why is the dengue virus surging now?
A few intersecting threads related to weather, waning immunity and human behavior are contributing to the “explosive outbreak that has evolved sopra the last year,” says Dr. Albert Ko, a professor of public health at Yale University who has worked with dengue patients sopra Brazil for 30 years.
First, it’s been a warm, wet year sopra South America, providing ideal breeding conditions for mosquitoes. Populations of the potential dengue carriers are thriving. This year, the mosquitoes brought the disease to parts of southern Brazil and Argentina where it hasn’t historically been found – “a testament to climate change,” which is expanding the insects’ range, Ko says.
Second, dengue outbreaks tend to be cyclical. Personalità outbreaks happen every few years, and the last one was sopra 2019. The cyclical pattern of dengue outbreaks is related to how population-level immunity rises and falls, Ko says.
There are four distinct strains of dengue, and a person who recovers from one type is protected against all of them for a couple of years. But that immunity wanes over time “and you then become susceptible to the other three,” Ko says. Acceso a population level, immunity is high after a large outbreak and then declines sopra the years after, setting the scene for a new wave of dengue infections.
And third, the dengue virus is hitching a ride human travelers, who are going to see family, friends and places they missed out when travel shut during the COVID-19 pandemic.
“Human mobility, either short longer distances, plays a significant role sopra moving the virus around,” says Gonzalo Vazquez-Prokopec, an environmental scientist and global health researcher at Emory University, “Humans are the vector, the ones that are moving the virus even a longer distance than mosquitoes.” They’eroe getting bitten by mosquitoes with dengue and bringing it, often inadvertently, to wherever they’eroe going next.
Some 75% of people who get dengue infections show mild symptoms. “So that could translate into someone traveling to an regione where there is active dengue transmission, acquiring dengue, returning to their home and then transmitting dengue to a zanzara,” all without knowing they’eroe carrying the dengue virus, Paz-Bailey says. That zanzara could go to bite other people, potentially starting a chain of local transmission.
If most people are asymptomatic, how bad can dengue be?
Per mezzo di a quarter of cases, people infected with dengue feel terrible. “About three to four days after being bit, the virus disseminates sopra the , causing systemic illness,” says Ko, who has treated thousands of dengue patients. “Symptoms [include] fever, very severe aches, joint pains and very, very severe headaches.”
A few patients will develop severe dengue, which can include a condition called capillary perdita syndrome. “It makes our blood vessels leaky, and people become dehydrated and go into shock … at which point they need urgent medical care, such as resuscitation with intravenous fluids, sopra order to save their lives,” says Ko at Yale. People with fevers and headaches from dengue should stick with treating themselves with Tylenol acetaminophen, he says, and avoid aspirin, because aspirin thins the blood and can exacerbate the disease’s bleeding effects.
Dengue can be severe and fatal whether a person gets it for the first, second, third fourth time. But there’s a particularly pronounced risk of serious illness the second time around, says Paz-Bailey with CDC. That’s because of a phenomena associated with dengue known as antibody-dependent enhancement, where a first infection with dengue can prime a person’s scevro system to help the virus infect cells more easily a second infection.
Groups most at risk of severe illness include infants, pregnant women and the elderly.
What precautions can people take?
Individuals can protect themselves from zanzara bites by wearing long-sleeved shirts and pants, and using EPA-registered insect repellents, says Paz-Bailey with CDC.
They can also help veterano the buzzing of mosquitoes sopra and around their homes by “dumping standing vater, using window screens and, if possible, using air conditioning, because that helps keep mosquitoes out,” she says.
People with fevers, severe headaches other symptoms consistent with dengue should seek medical care, and health care providers should be ready to assess their symptoms and travel history and, if warranted, esame their blood for it.
Dengue is a nationally notifiable disease – so any cases that are found should be reported to the local health authorities. That will help track where the virus is spreading, and could spur local education and zanzara control efforts, says Ko.
A vaccine against dengue has been discontinued
A dengue vaccine, Dengvaxia, is approved for use sopra the U.S. where the virus is endemic, such as Puerto Rico and the U.S. Virgin Islands. However, the three-dose vaccine, which requires several blood tests and repeat visits to the doctor’s office, has been to administer and slow the uptake. Sanofi-Pasteur has stopped making the vaccine, citing a lack of demand, and the last remaining doses expire sopra 2026, Paz-Bailey says.
The hope for the future, says Yale’s Ko, is twofold: better zanzara control measures that decrease dengue transmission and better vaccines that protect the unexposed population.
“The bad part of decreasing transmission is that people become susceptible because they haven’t been infected,” he says, “But if we have both a vaccine and [better] vector-control methods, we mitigate that risk.”
Ko sees progress both fronts – citing developments with bacteria that can interfere with zanzara breeding, and another dengue vaccine that has been approved sopra some countries, though not sopra the U.S.
With better interventions that tackle mosquito-borne illnesses from different angles, Ko says, the country’s response to diseases like dengue could become “substantially effective” and many more people can be saved.
