The Deadly Virus That’s Spreading Faster Than Malaria or West Nile

A boy with dengue disease sleeps on a chair in Manila, Philippines. Many of the people who develop hemorrhagic fever from dengue will be children. (Photo: Nicolas Asfouri/AFP/GettyImages)

The Disease Daily is a publication from HealthMap at Boston Children's Hospital.

About half of the world is at risk of a virus that Americans don’t know at all. For Americans, dengue fever is about as foreign as the metric system or the leading contenders in next year’s World Cup. But while we don’t know much about it, for the rest of the world, dengue is part of life.

Unless you live in Puerto Rico, pretty much all U.S. cases of dengue—a virus transmitted by mosquito bites—are acquired while traveling abroad. Beyond our borders, though, dengue fever has become a very big problem very quickly, and there’s still no cure. (Even Puerto Rico had over 12,000 cases in 2010, says the Centers for Disease Control.)

How a Virus Changes the World

Every year, around 500,000 cases of dengue will progress to life-threatening hemorrhagic fever; a large portion of these cases will be children. Even in a year without particularly bad local epidemics, 2.5 percent of the patients who develop hemorrhagic fever—12,500 people—will die.

Nearly half of the world’s population is at risk for dengue, which primarily affects cities in tropical and subtropical regions, according to the World Health Organization (WHO). What’s most troubling about dengue is just how quickly the virus has emerged onto the global stage: Over the last 50 years, the number of new cases has increased 30-fold. Today, the WHO estimates there are between 50 and 100 million dengue infections worldwide annually. Last year, it called dengue the “most rapidly spreading mosquito-borne viral disease” in the world—faster than West Nile virus or malaria.

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A friend of mine, a Peace Corps volunteer in the Dominican Republic, contracted dengue in October 2009. She knew right away from the aches in her ankles and wrists, which lasted two days before the fever and splitting headache hit. She didn’t go to the doctor until several days later, when she’d developed a splotchy rash. At the hospital, blood tests confirmed she had dengue.

Over the course of her service in the Peace Corps, she got the symptoms again (most likely another strain of the virus), but didn’t go to the doctor in town. It seemed too far for something she knew would probably pass.

My friend’s decision not to seek medical attention isn’t unique, and much of the time those who are afflicted never see a doctor. Because the symptoms of dengue are not immediately life-threatening, and often mirror those of malaria, many cases go unreported. As a result, current estimates of dengue cases are probably low, especially in poor countries with few resources.

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Thankfully, my friend was spared a case of dengue that escalated to hemorrhagic fever, as often happens in recurring cases. Hemorrhagic fever is especially brutal, including bleeding gums, bloody vomit, and organ failure. Even the joint pain can escalate to unbearable levels, which is how dengue got its pseudonym, “Break Bone Fever.”

Most cases of dengue are transmitted via the Aedis aegypti mosquito. After the mosquito acquires the virus by eating human blood, it can carry dengue for the rest of its life and transmit the virus to anyone it bites. One of the reasons dengue cases have increased in recent decades is urbanization; Aedis aegypti live mostly in man-made habitats, says the WHO. Specifically, they love to breed in the puddles and stagnant water that are ubiquitous in cities without municipal water and sanitation systems.

There’s a second reason behind the rise of this devastating virus, though: climate change. In short, by burning fossil fuels and tearing down forests, humans have been contributing to increasing temperatures and changing rainfall patterns, which, in turn, have made it easier for mosquito-borne diseases to thrive in tropical and subtropical areas. This means that dengue isn’t isolated to poor, faraway countries anymore. In addition to the inroads it’s made in Puerto Rico, Europe is now facing its first dengue outbreak since the 1920s; the Portuguese archipelago of Madeira reported 2,164 cases of dengue in early February 2013. And that makes dengue a virus we all need to watch.

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Even more worrisome is that there is no cure. Recent trials on a vaccine in Thailand fell short of expectations, though research continues. Which means our only defense for now is to cut the number of mosquitoes—by killing the bugs and destroying their breeding habitats—and limiting exposure to mosquitoes by wearing repellent and covering up with clothing. But for the 125 countries where dengue lives, both of these efforts would require a massive public health campaign. To make matters even more complicated, Aedis aegypti mosquitoes are pretty crafty—hiding in tires and shipping containers to travel from country to country—and another species of mosquito responsible for dengue in Europe and Asia, called Aedis albopictus, can hibernate to survive colder temperatures.

Dengue is, without a doubt, a global problem. So while Americans have managed to pass the last several decades without learning kilometers or the planet’s best soccer players, it’s time for us all to get up to speed on the world’s fastest-emerging virus.

--by Jason Hayes

Have you heard of dengue fever? Have you ever experienced it or know someone who has?

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