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Unsuspecting U.S. Travelers Bring Novel Disease Home, And It Spreads

When a disease threat looms, you might expect that everyday people won’t recognize the danger, but professionals will. That isn’t always the case, though. Some data made public last week demonstrates that even people well-informed about risks can be vulnerable—and underlines the threat that one new disease poses to the United States.

Last week was the annual conference of the Epidemic Intelligence Service of the US Centers for Disease Control and Prevention, the ferocious young disease detectives who are the CDC’s SWAT team for outbreak response. (Don’t they sound intriguing? Look, here’s a book about them.) At the conference, EIS officer Dr. Alex Millman described what happened when a US volunteer organization sent its members to work in the Dominican Republic for stints of 4 to 8 weeks. The Dominican Republic is a hot spot for diseases carried by insects, and so the volunteers and staff attended health briefings ahead of time and talked to their own doctors. During their assignments, 96 percent of 102 whom Millman interviewed wore insect repellent and slept under a bed net. And yet, after they returned, almost half of them, 46 percent, were diagnosed with chikungunya.

If you haven’t heard of chikungunya yet, don’t worry: You will.

Chikungunya is a mosquito-borne disease that causes fever and crippling joint pain that can be long-lasting. There is no vaccine against it, and no specific treatment, other than rest and pain-killers.  It has a long history in  Asia, but is a new arrival in this hemisphere: It was first detected late in 2013, and spread through the Caribbean and Latin and South America with explosive speed. There have now been more than 1.4 million cases, according to the Pan American Health Organization, and as the disease-tracking group CIDRAP noted on Monday, the count is increasing by thousands more each week.

And some of those are in the US. Travelers returning home have brought chikungunya with them: There have been 93 lab-confirmed cases in 24 states so far this year, according to the CDC, and there were 2,481 cases last year, in every state except for Alaska, North Dakota and Wyoming.

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map from CDC.gov; original here.

Those cases are important, not just for the suffering of those individuals, but because they pose a threat to people who have not traveled. Sooner or later, someone arrives back in the US at a point in their disease where virus in their blood can be picked up by a local mosquito, risking the start of a chain of infection here—a place where most doctors are still unfamiliar with the disease. That’s not idle speculation. First, the mosquitoes that carry chikungunya range widely across the southern US—and, with warming temperatures, are moving north.

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maps from CDC.gov; originals here.

And, second, this has already happened once: Last year, 11 people in Florida came down with chikungunya without having left the state.

This is the same pattern that led to the reintroduction of dengue in the US (which I covered for Slatecovered for Slate in 2012): outbreaks in the Caribbean and South America, and then travel-associated outbreaks in the US in places with the right mosquito species, and then re-establishment of the disease within US borders.

Unfortunately, there is no easy fix. But for their own sake and their neighbors’, travelers can do their best not to be a vector. As the volunteers’ experience shows, though, that is more difficult than it seems: They took the recommended precautions and almost half of them still became infected. The one gap in their armor, detected in Millman’s survey, was that few of them slept in rooms where windows and doors had screens. That demonstrates that it can takes layers of protection to prevent mosquito bites—in some cases, literally layers: the CDC recommends long pants and long sleeves to keep the bugs away.

Except: People don’t go on Caribbean vacations, or even work or volunteer trips, with the expectation that they will be wearing muffling clothing and staying indoors; they go to loll on the beach, hang out in hammocks, and wear as little as possible for as long as they can. Those are reasonable expectations, going to the tropics. It’s possible that coming home with an illness is now a reasonable expectation as well.