I hate mosquitoes so much that I bring my own bug repellent to parties. But in early March, on a trip with my partner to the idyllic island of Curaçao off the coast of Venezuela, I was caught off guard by insect bites after our bed-and-breakfast hosts said that mosquitoes didn’t usually appear until late summer.
Near the end of the vacation, my legs began to ache. After I couldn’t keep up with my partner on a snorkeling adventure, he pulled me from the water. My ribs felt broken, as if I’d been smashed against large boulders in the sea. Later that day came intense fever, alternating with shaking chills.
Back in Michigan — weak, nauseated and dehydrated from explosive diarrhea — I ended up in the emergency department. Tests showed concerning white blood cell levels and abnormal liver numbers. The physician assistant who saw me was perplexed; she gave me IV fluids, medication for nausea and sent me home.
A few days later I developed itching so severe that I couldn’t sleep. A bright red rash spread over both thighs and up my lower back. My brain was foggy, and my balance was so impaired that I would have failed a sobriety test. My primary care doctor had no answers. But as my head began to clear, it occurred to me to request a dengue fever test.
Two days later, the test was positive.
Despite my training in medicine, I was blindsided. Dengue, a mosquito-borne illness, is surging through Latin America and the Caribbean, including in Puerto Rico, where a public health emergency was declared last week. This year is likely to be the worst on record, in part because of El Niño-driven temperature spikes and extreme weather linked to climate change. As temperatures rise and precipitation patterns grow more erratic, the problem will get only worse.
But neither the traveling public nor our frontline health workers are prepared. Without urgent reforms to how we educate travelers, doctors, nurses and others — as well as reforms to public health surveillance and early warning systems — we will be doomed to miss textbook cases like mine. That means those infected with dengue will miss out on timely treatment, possibly even spreading the virus to areas where it has never been found before.
Dengue virus, which is transmitted by the Aedes species of mosquitoes, infects up to 400 million people every year in nearly every region of the world, but it is most prevalent in Latin America, South and Southeast Asia and East Africa. Most cases are asymptomatic or, like mine, are considered mild, but 5 percent progress to a severe, life-threatening disease including hemorrhagic fever.
One malicious feature of this virus is that when someone is infected a second time with a different type, the risk of severe dengue is higher. A vaccine exists, but the Centers for Disease Control and Prevention recommends it only for children between 9 and 16 who have had dengue before and live in places where the virus is common. That’s because, paradoxically, if you’ve never had dengue, the vaccine puts you at greater risk of severe illness your first time.
Dengue outbreaks, which, in the Americas, tend to occur cyclically every three to five years, now appear to be expanding their geographic reach as temperatures climb. The Aedes mosquito has typically had difficulty surviving and reproducing during the winter in temperate climates. But in parts of Brazil, which currently faces a dengue emergency, the thermometer no longer dips as low in the winter as it once did, allowing the bugs to reproduce year-round. Overall, Latin America and the Caribbean have had three times the number of cases this year as reported for the same period in 2023, which was a record year. Higher temperatures are also helping the virus develop faster inside the mosquito, leading to a higher viral load and a higher probability of transmission. And mosquitoes are benefiting from standing water from rains and floods that are growing more extreme in a warming world.
As the virus spreads globally, travelers are bringing infections back to the continental United States. Based on 2024 numbers to date, this year should show a clear increase of cases here at home compared to 2023, given that the typical dengue season hasn’t even started yet. There could also be local outbreaks in places like Florida, Texas and California, which have experienced small ones in the past. As Dr. Gabriela Paz-Bailey, chief of the Centers for Disease Control and Prevention’s dengue branch, told me by email, “Increased travel to places with dengue risk could lead to more local transmission, but the risk of widespread transmission in the continental United States is low.”
But since testing is done only on a small fraction of cases, many are going uncounted. I was the one who requested that I be tested. Had I not been given a diagnosis, I would not be aware of my increased risk of severe illness if I am reinfected. Getting a diagnosis is crucial to inform those infected in areas where the Aedes mosquito lives so that the virus doesn’t spread further.
The growing risk means travelers to regions with dengue must be savvier: They can check local news and U.S. State Department advisories, bring an effective insect repellent and protective clothing and book lodging with air-conditioning or screens on the windows and doors. Though the Aedes mosquitoes now live year-round in many locations and are pushing northward into new regions thanks to climate change and other factors, there are still seasons where the risk is greater, and travelers might consider avoiding trips during those periods. Travel insurance with medical coverage may also be a useful precaution.
For medical professionals, this should be a warning. We need to start thinking about dengue as a possible diagnosis, not just a piece of textbook trivia. We should ask about recent travel when treating patients presenting with symptoms, especially symptoms not easily explained by other diagnoses.
Medical schools are gradually integrating climate change effects into curriculums. This is essential since malaria, Lyme, West Nile and other insect-borne diseases are on the rise, as are other climate change-exacerbated conditions like heat illness, asthma and allergies. This work must accelerate, and training must include those of us who are already practicing. State medical boards should consider mandating continuing education on tropical emerging illnesses, as they do on many other pertinent topics.
After receiving my positive test result, I called the emergency department to leave a message for my previous provider about my diagnosis, assuming she had never before seen dengue. If we continue on this trajectory, I’m certain this won’t be her last case.
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