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Claire Panosian Dunavan is a professor of medicine and infectious diseases at the David Geffen School of Medicine at UCLA and a past-president of the American Society of Tropical Medicine and Hygiene.
Readers, sometimes I wish we could meet face to face and talk. If so, today I would ask: who here has dealt with the world’s most common mosquito-borne virus and poster child for the 21st century’s explosion of epidemic, vector-borne blights?
My guess? Some of you have seen travelers with dengue, the miserable, achy woe spread by day-biting, often urban Aedes mosquitoes. Perhaps a few, like me, have also encountered a patient who contracted the infection here in the U.S. But even if you haven’t yet seen a case, chances are you soon could, according to a recent Health Advisory from the CDC.
Let’s start with some ominous numbers in the CDC alert. While 2023 saw 4.6 million reported cases of dengue in the Americas, this year’s count (as of June 24) had already doubled, reaching 9.7 million. And that’s before much of the region would have entered its highest-transmission months. Gulp.
Of course, most U.S. cases of dengue stem from overseas travel, which, thanks to waning concerns over COVID, has now bounced back. But as more people travel, local cases can also climb because at least 30 U.S. states harbor the two black-and-white mosquitoes — Aedes aegypti and Aedes albopictus — that can easily transmit dengue from a viremic carrier to someone else.
Finally, don’t forget that autochthonous transmission within our borders is nothing new. Although the virus wasn’t isolated until 1945, dengue epidemics are thought to have occurred in major southern cities and Philadelphia in the 18th and 19th centuries. In the 1980s, dengue re-emerged, periodically causing both small local outbreaks and sporadic cases in Florida (the state with the most cases), Hawaii, Texas, and — in the last 2 years — Arizona and California.
How Did We Get Here?
At present, 3.6 billion people in over 100 countries live in dengue-endemic areas. As a result, the world is now experiencing an estimated 400 million yearly infections, which, in turn, produce 100 million clinical illnesses and 21,000 deaths largely affecting children.
Key contributors to this dramatic change in a once-neglected tropical disease include the following:
The global spread of dengue’s four serotypes, which has often led to several strains circulating in the same highly endemic placeThe expanding distribution of Aedes aegypti and Aedes albopictusAedes mosquitoes’ predilection to breed in man-made, peri-domestic habitats (think anything from a flower pot to a cistern to a spare tire) and bite multiple people in quick successionThe unprecedented urbanization and human crowding recently seen in many tropical countries
Finally, our warming world is also fueling dengue’s perfect storm because rising temperatures lead to faster replication of the virus, more fecund vectors, higher bite rates, and longer seasons of transmission.
A Tale of Two Patients
In 2002, I published a story in Discover magazine about an East Coast couple whose South Pacific honeymoon quickly spiraled from tropical bliss to tropical nightmare.
First, the newlywed I called Suzy (not her real name) developed teeth-chattering chills, fever, and myalgias. Then, after a brief respite, her fever roared back, along with a furious headache, florid petechial rash, and bleeding gums. Urgent calls were made, a flight booked, and — 24 hours later — a wan, clammy bride whose illness practically screamed “dengue” landed in my hospital. There she received careful hydration and monitoring, plus empiric antibiotics while her scarily low blood pressure and platelets slowly normalized.
Still shaken and aching, Suzy and her husband then flew home and, a week later, her dengue antibody returned positive. Happy ending? Not quite. Like many dengue sufferers, she remained severely fatigued for the next several months.
Looking back, Suzy’s saga taught me an important lesson. Although the full-blown (and potentially fatal) syndrome now called “severe dengue” typically follows a second infection with a heterologous strain, even primary dengue can sometimes cause bleeding and shock.
Now meet my writer-friend Roxanne who spent the 2013 Labor Day weekend in Austin, Texas. After returning home, Roxanne also fell sick, but unlike Suzy, her fever, body pain, headache, and rash remained a mystery until a non-medical friend remembered something he once read in a newspaper.
“Hey, what about that weird disease in Key West transmitted by mosquitoes?” he asked Roxanne a couple of weeks into her illness. “Den-something. Den-dee? Den-go? Den-gay?”
And here’s the rub. Even though she had already been seen by a colleague who ordered many exotic tests, no one, myself included, thought about dengue until Roxanne herself requested one more serology, which confirmed her pal’s savvy hunch.
Advising Travelers, Awaiting Vaccines
David O. Freedman, MD, is a travel medicine expert at the University of Alabama at Birmingham, who, for two decades, ran the Gorgas tropical medicine course in Lima, Peru. One highlight featured by the program is a field trip to the Amazon to see inpatients in Iquitos. Freedman noted that since the trip overlaps with the peak season for dengue, the hospital at times couldn’t admit people with other tropical diseases “because all of the beds were already filled with dengue patients” with bleeding, jaundice, hypotension, respiratory distress, you name it.
Freedman himself luckily dodged dengue all those years by following the same, time-honored precautions we still advise today. Despite “the hottest jungle climate you can imagine with maximum humidity,” he always wore long sleeves and pants, applied lots of repellent containing DEET or picaridin, and never ate lunch or dinner outdoors.
Freedman is also closely watching the development of new vaccines for dengue. The good news: a new vaccine was recently endorsed by the WHO for people up to 60 years of age (but prioritized for 6- to 16-year-olds) in highest-transmission settings like Iquitos. But, as Freedman discussed in a paper in the Journal of Travel Medicine, what about travelers?
I raised that same question when we spoke on the phone. Specifically, could Takeda’s new Qdenga vaccine also protect a long-term dengue-naive expat or U.S. medical worker in a high-risk setting?
Right now, there are many unknowns, Freedman told me, and Qdenga is not yet approved in the U.S. But the WHO recently suggested that Qdenga could at least be considered for such long-stay travelers. Meanwhile, as we spoke, I could see the wheels turning in his head. He hopes that in the next 5 years we’ll have next-generation vaccines that fully protect against all four dengue serotypes and shield far more people from a blight that, it now appears, will continue to plague humanity for a long, long time.
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