The dengue fever virus is the most common virus that mosquitoes transmit and infects about 100 million people worldwide every year, killing about 25,000. In spite of this frequency, though, the United States, with the exception of Puerto Rico, has been mostly dengue-free for decades—until 2009.
That year, a woman in New York turned up with a dengue infection, having just returned from a trip to the Florida Keys. Her case was the first of a handful that led public officials to conduct a survey of the Key West population. To their shock, they found that about 5% of residents, or about 1000 people, showed evidence of dengue exposure in 2009.
The mosquito that carries the virus occurs in warm areas of the country, including Florida and Texas, and indeed, isolated cases of dengue have cropped up a few times since the 1980s along the Texas–Mexico border. But the cases in 2009 and more in 2010 have authorities concerned that dengue now has achieved an intractable foothold on the continental United States.
Wearing repellent when in areas where they occur is one tactic. Another is removing breeding places, such as any containers with standing water. The precautions apply wherever you’re going, whether to areas where dengue is already endemic or where it is emerging. The CDC provides regular updates for travelers, including a page specific to the Florida cases.
Dengue fever can hit hard or harder, depending on the symptom severity. The “mild” version of the disease can involve a high fever, a rash, severe headache and pain behind the eyes, and nausea and vomiting. Given that these symptoms are largely nonspecific, if you see your doctor about them and have traveled in a place where dengue fever occurs, be sure to mention it. A more severe form of dengue fever is dengue hemorrhagic fever, which begins much like the “mild” form but then progresses to symptoms that can include nosebleed and signs of bleeding under the skin, known as petechiae. This form of dengue can be fatal.
The most severe manifestation of the disease, dengue shock syndrome, includes the symptoms of the milder forms along with severe abdominal pain, disorientation, heavy bleeding, and the sudden drop in blood pressure that signals deadly shock. Onset is typically four to seven days after exposure, and the mild form usually lasts only a week, while the more severe forms can involve either a progressive worsening or a sudden worsening following an apparent improvement.
Oddly enough, having dengue fever once does not mean you’re safe from it. Indeed, some studies indicate that a second bout of dengue fever often can be worse than the first, with a greater risk of progressing to the hemorrhagic form.