Aedes aegypti, the principal vector for the spread of chikungunya. Photo by João P. Burini
In the southern United States, it’s that time of year again: Birds are chirping, the sun is shining, and thousands of baby mosquitoes are hatching in your weird uncle’s neglected swimming pool.
But this year there’s a new problem child: Aedes aegypti, otherwise known as the yellow fever mosquito. Typically brown with white markings, this mosquito is a highly aggressive biter, generally found in hot, humid areas like Mexico and Central America, and sometimes the American south. But this year, mosquito control managers were concerned to find a bunch of Aedes aegyptias as far west as southern California, and they’re multiplying quickly. The female of the species lays up to 200 eggs several times a season, just above the water line in containers of standing water.
Aedes aegypti is the perfect vector for a handful of frightening tropical diseases, including yellow fever, West Nile virus, and dengue fever. But they’re also a great transmitter of a little known virus that’s been popping up in the Caribbean this year: Chikungunya.
Chikungunya is an acute virus transmitted from the bite of an infected mosquito. It’s not usually fatal, but it causes acute fever, joint pain, and rash. What’s scary is that it has a strikingly high rate of epidemic—up to 50% of potential human hosts will contract the disease when bitten. And of those, around 10% will have persistent arthritis in the smaller joints for up to three years. There’s currently no vaccine to prevent or medicine to treat the disease—the best thing we’ve got is bug spray.
In late 2013, the virus was found for the first time in the Americas, on islands in the Caribbean. More than 5,900 suspected cases of chikungunya have been reported in the Caribbean and South America since December 6. The Public Health Ministry of the Dominican Republic recently reported 3,690 suspected cases in the San Cristobal province alone. Although this may not sound as bad as a disease like Ebola (which kills you through internal hemorrhaging in your gastrointestinal tract), a full-blown outbreak of chikungunya, replete with hundreds of southerners experiencing long-term arthritic symptoms and fever, would take a serious economic toll on the isolated rural areas of the deep south.
So, on to the question: How worried should we be about this particular disease? I called up Dr. Tim Brooks at the Rare and Imported Pathogens Department of Public Health England (PHE). He’s been helping to run the main UK referral center for the disease out of the PHE office, so I figured he’d be able to tell me whether or not you should cancel your upcoming vacation to New Mexico.
Health workers identifying chikungunya in a patient after the disease traveled to the south of France via a tourist. Photo courtesy Valentin Pezet, Jules Foulongne, and Nicolas Gueniot
VICE: So what exactly is Chikungunya? What is it named for?
Dr. Tim Brooks: Chikungunya is a disease that’s pretty much had its day, but it comes around every so often. Its name translates to “that which bends up,” because the biggest problem with the disease is the arthritic debilitation that follows the infection. It’s also got a fascinating history: Chikungunya was first pinned down in Tanzania in 1952, but historical accounts appear across Asia and Africa as early as 1779. Historically, outbreaks began in the Indian Ocean Basin, and it’s been able to travel very successfully since then.
What are the symptoms exactly?
Normally chikungunya presents with joint pains, a rash, and acute fever, followed by all the other symptoms you associate with high fever: headache, diarrhea, back pain. The main problem is the arthritic pain, which does not go away for maybe 10% of patients. It can persist for up to three years, and is very debilitating. It tends to affect the smaller joints, causing local swelling and pain. Once you’ve got it, you’ve got a lifelong immunity to it, but it will generally infect a large portion of the population, move on, and then disappear until the next generation comes up.
How does it travel?
Chikungunya survives in closely connected landmasses, but it’s also possible for someone who travels with it to spread the disease during the incubation period, when mosquitoes in a new territory bite them and contract the disease. We’ve seen this in the last major epidemic, which was in 2007. That was really fascinating. The virus spread way beyond where it’d ever gone before, and most importantly, it had a single base mutation, where one nucleic acid changed.
Rash commonly associated with chikungunya
Whoa. What happened after that change?
Well, it certainly increased the virus’s virulence, and cases became more severe. But it also altered its mosquito tropism. Instead of being confined to be spread only by the yellow fever mosquito, the virus evolved to use the tiger mosquito as a secondary vector. This mosquito is from Southeast Asia, and it’s a very tough little bug. It’s famous for traveling around the world in motorcar tires.
Wait, what? These mosquitos breed in tires?
[Laughs] Yes, motorcar tires shipped worldwide often have water in them, and the mosquitoes can live and breed in that water, and then establish themselves around the world.
So exactly how virulent is this disease?
Chikungunya has an extremely high attack rate in a vulnerable population. Up to 50% of people susceptible to the disease get it, and it has a very high rate of epidemic. The problem is that many countries that are currently experiencing cases don’t have the ability to properly handle it. If you look at the number of suspected cases in parts of the Caribbean, there are reports of 1000 cases, but only 1400 confirmed cases. Part of that is that they don't have the resources to identify it.
How bad do you think it could get in the southern United States?
Well, it could start in the south with a single tourist. Then, imagine a school kid comes into school with the disease. You might have some cases in that area, and whether or not the disease will spread depends on public health. If you cut back the number of mosquitos, you can cut back the potential for an epidemic. But many people in the rural areas of the south don’t necessarily have access to hospitals, or even health care. It’s those areas that I’m concerned about.