But a recent study suggests the United States has a bit of time on its side. The strain of chikungunya circulating in the Caribbean is the Asian strain, and it’s only adapted to be carried by the Aedes aegypti mosquito, says Scott Weaver of the University of Texas Medical Branch, who’s been studying the virus for years. And so far, that mosquito can only be found in the far southern U.S.
Still, health officials are pretty certain that chikungunya will eventually take hold in the United States, the way it has across the Philippines, Africa and countries bordering the Indian Ocean.
Chikungunya is an unnerving virus because of the painful symptoms it causes — a searing pain in the joints that can make the slightest move agonizing. And the pain can persist for weeks or even months. The name in the Makonde language, spoken in Tanzania and Mozambique in Africa, refers to the painful contortions seen in so many patients.
The symptoms are mild at first and travelers can carry the virus around without knowing they are infected. The 129 cases of chikungunya reported in the U.S. so far this year have all been carried by travelers.
People infected once are immune for life to re-infection, but that doesn’t do Americans much good, says Dr. Pilar Ramón-Pardo of the Pan American Health Organization. “There was no chikungunya in the Americas before, so all the population is vulnerable to chikungunya,” she told NBC News.
“A lot of people are traveling with the virus without knowing it."
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Weaver, whose team is working on a vaccine against chikungunya, said a genetic study shows there are two distinct strains — one that can infect and be passed along by Aedes aegypti and another that lives in Aedes albopictus — the notorious Asian tiger mosquito.
That’s the stripey one that bites in broad daylight and that’s spread across much of the U.S.
“For the moment, at least, the Asian strain that is in the Caribbean … doesn’t have same capacity to adapt to Aedes albopictus,” Weaver told NBC News. “For us in the U.S., it’s a little bit of good news,” he added.
“The strain that is in the Caribbean now could cause some outbreaks in the southern United States but it is unlikely to in northern latitudes. Unfortunately for Latin America and the Caribbean, the virus is going to do just fine with only A. aegypti.”
It doesn’t take much to bring the virus to new territory, Ramon-Pardo says.
“You have the person with the disease, a mosquito bites them, and the mosquito can disseminate the virus. Then it will spread,” she said.
“A lot of people are traveling with the virus without knowing it,” added Weaver.
That’s happened with three untreatable viruses in the past 15 years — West Nile, dengue and now chikungunya.
It’s easy to predict where chikungunya will take hold. Just look for dengue. The A. aegypti mosquitoes that carry dengue also carry chikunguyna. “If they have epidemics of dengue, then it’s possible to have an epidemic of chikungunya,” says Ramon-Pardo. “We have it in central America.”
And dengue is moving into the United States, especially in Florida and south Texas. Three people have died recently in the U.S. from dengue.
Because people with flu-like illness so rarely get tested for anything, the Centers for Disease Control and Prevention says no one knows how common dengue really is in the United States. It only gets noticed when it causes serious diseases — either neurological disease or, worse, hemorrhagic fever, which causes a rash and internal and external bleeding.
West Nile is much more common. Since it was first spotted in 1999 in New York, it’s been diagnosed in close to 40,000 people and killed 1,668.
West Nile virus causes fever and aches and usually isn’t serious. But in some people it can spread to the brain or spinal cord, killing them or causing paralysis.
No one’s sure precisely how West Nile arrived in North America, but it has now been reported in all 48 contiguous states, as well as parts of Canada and Mexico and all the way to Argentina.
The virus has a life cycle that takes it from mosquitoes to birds and back into mosquitoes that bite people, so it could take hold quickly, unlike viruses that only infect people.
Mosquitoes carry other diseases, also, such as Eastern equine encephalitis. Standing water, even in extremely small containers, can breed mosquitoes. CDC says people should wear long sleeves and use insect repellent that contains DEET, picaridin, IR3535, or para-menthane-diol (PMD).
The CDC helped eradicate malaria in the United States in 1951 and modern living is likely to keep it at bay, says Weaver. Screens, air conditioning and spraying for mosquitoes all help control the outbreaks.
But not forever. “The prospects for chikungunya are not good,” he said. It’s only a matter of time, he said, before the virus adapts to Aedes albopictus, the Asian tiger mosquito, or until someone imports the strain that is adapted.