Dengue Fever Creeps Back Into the U.S. — and Climate Change Isn’t Helping

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Dengue fever is nasty. Transmitted by the bite of the Aedes aegypti mosquito, dengue infects an estimated 220 million people a year — 2 million of whom develop a severe form called dengue haemorrhagic fever, which has no known cure. And it can be extremely painful.

When I wrote a piece in 2002 about the reemergence of dengue fever in Hong Kong, TIME foreign correspondent Tim McGirk described the experience of contracting the disease this way:

There’s a reason they call it break-bone fever. You feel like there’s this deep, painful itching happening inside your bones. You’re on this horrible roller-coaster ride of hot spells and chills, like you’re being shaken around. It just racks your body.

Dengue fever is most common in the poorer areas of Latin America and Asia, and cases were virtually unheard even in the tropical reaches of North America, where anti-mosquito efforts were able to keep the fever at bay. But as Greg Allen reported today for NPR, that’s begun to change. The first native cases of dengue fever in Florida in more than 70 years began appearing in Key West in 2009, and they’re becoming more common:

Dengue is considered a serious public health threat in Key West, Hawaii, south Texas and other Florida counties where it has been reported. But compared with its resurgence in Latin America, the outbreak in Key West is relatively minor.

The growth in global trade and international travel helped bring dengue to the U.S. But [Mark] Whiteside [medical director at the Monroe County Health Department in Key West] says there’s another important factor — the Aedes aegypti mosquito.

“The carrier of dengue, the vector of dengue — the Aedes aegypti — is more widespread and abundant than ever before in history. That’s obviously part of the reason we have dengue back,” he says.

It’s not clear why the mosquito has become more abundant. The bug lays its eggs in still pools of fetid water — exactly the sort you might see in a construction site or an unattended pool — so the growth of urbanization throughout Latin America and Asia may have helped the viral disease to spread.

Then there’s climate change. As the weather warms, especially in the tropics, the mosquito is able to thrive and expand its potential range. A 2008 report by the Lowy Institute in Sydney estimated that by 2085, more than half the world’s population will be living in areas that are at risk for dengue fever, far greater than today. In general, vector-borne diseases like malaria and dengue and West Nile Virus could become more prevalent as the weather warms and the winters that once stopped these mosquitoes cold become less of a barrier.

But it would be a mistake to assume that climate change is the only risk factor behind dengue and other mosquito-borne diseases — or even the most important one. Proper public health measures — spraying to kill mosquitoes, clearing out stagnant water, even using mosquito-eating fish — can stop the spread of the disease even in tropical areas that are welcoming to the insects.

That’s why wealth may be as important as temperature; dengue and malaria are relatively rare in tropical Singapore, thanks to the government’s military mindset on the disease, but the disease is far more common in nearby Kuala Lumpur, which is much poorer. Malaria was a hazard of living in Florida through the middle of the 20th century, but pesticides and public health effectively eliminated the disease.

The best hope for rich and poor nations alike would be an effective vaccine — and with dengue fever, one may be close. France’s Sanofi Pasteur has reported very promising results for a dengue vaccine trial that’s ongoing in Thailand, and the vaccine is due for release by 2014. The Thai trial began in 2009, and so far none of the 4,000 children involved have shown adverse reactions — always the first step for a vaccine trial.

Reducing carbon emissions are a must for lots of reasons, but when it comes to tropical diseases, I’d put my faith in a good vaccine.

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