Chikungunya is coming to the United States. The question is not if, but when. How will the mosquito transmitted viral illness affect Americans? What can be done to prevent an infection?
Until Dec. 2013, the chikungunya virus was not found in the Western Hemisphere. There had been cases of illness that were imported from other parts of the world but none had been acquired locally. That all changed with the detection of the viral illness on the French half of the island of St. Martin in the eastern Caribbean in very early Dec.
Since that time, the number of illnesses that have been confirmed or suspected has grown into the tens of thousands. The largest current chikungunya outbreak is on the island of Hispaniola, shared by the nations of Haiti and the Dominican Republic. The only current outbreak in continental North or South America is in French Guyana, on the northeast coast of South America.
Public health authorities had anticipated the arrival of chikungunya for some years. It originated in Africa but began a spread eastward about 2005 that would take it to the Indian subcontinent, Southeast Asia and to the Pacific Islands. Along the way, several genetic change occurred and the virus adapted to a second mosquito vector.
Aedes aegypti (the yellow fever mosquito) is the primary mosquito vector for chikungunya. It is a daytime feeder and feeds almost exclusively on humans and occasional other primates. The mosquito becomes infected with chikungunya after feeding on a sick person. The virus concentrates in the mosquito’s salivary glands and is then transmitted to anyone the mosquito bites for the remainder of its life.
The yellow fever mosquito is found in the tropics and sub-tropical regions of the world. In the Americas, it has reestablished habitat it lost during effective mosquito control programs in the 1940s and 1950s, including retuning to the United States. It has reemerged in the U.S., primarily in the southeast, though it has yet to regain all the habitat that pesticide use and control programs drove it from.
As the chikungunya virus emerged from Africa, genetic changes allowed it to infect Aedes albopictus (the Asian tiger mosquito). This species is also found in the tropics and sub-tropics but demonstrates several significant differences from the yellow fever mosquito. It is an invasive species in the United States where it was first discovered in 1985. While it competes with the yellow fever mosquito for habitat, it is also a hardier species and can be found in the summer as far north as Chicago and New York City.
The genetic changes that allow the Asian tiger mosquito to carry and transmit chikungunya have several implications. This species is less picky about which animals it feed on. It reproduces faster than the yellow fever mosquito. Its hardiness means that it can be found over a much greater range. This species is responsible for chikungunya outbreaks in Italy and France in the last decade. Where the two species compete for habitat, Aedes albopictus appears to be winning.
At this time, the chikungunya virus being transmitted in the Caribbean is of Asiatic origin and is transmitted only by Aedes aegypti. That said, the Asian tiger mosquito is not found on many of the islands currently dealing with chikungunya illnesses. Hispaniola is the first significant locale where the illness and the Asian tiger share geography. Scientists are monitoring the situation closely to see if the virus becomes transmitted by the Asian tiger mosquito.
Chikungunya is a viral illness. There is no cure, and no vaccine at this time. It is very rarely fatal but the youngest infants, and the elderly with co-morbid infections may be at risk of death. It is only spread through the bite of an infected mosquito, but little is known about its potential for transmission through blood transfusions, mother to fetus transmission or through organ transplants.
Symptoms of a chikungunya infection appear three to five days after being bitten and will last, in a best case scenario, for a week or so. The most common symptoms are fever and headache, chills, joint and muscle pain, swollen joints and a rash. The joint and muscle pain is debilitating for most patients and they often find themselves bedridden for several days. It could be termed “the summer flu.”
Many patients will suffer from joint or muscle pain for some time. Limited studies suggest that the pain may be persistent or relapsing, and this can last for as long as two years in about half of all patients. The severity of the original illness is one predictor for longer lasting pain. One study suggests that as many as ten percent of all patients may still have some form of muscle or joint pain up to five years after their illness.
Treating the illness means treating the symptoms. In general, medications containing ibuprofen, naproxen, acetaminophen, or paracetamol are used to relieve pain and fever. These are over-the-counter medications. Rest is also indicated as is drinking enough fluids to stay hydrated.
Preventing chikungunya means preventing mosquito bites. Both the yellow fever mosquito and the Asian tiger mosquito are aggressive day feeding species. The yellow fever mosquito is known to come indoors and hide in closets or in the shade under a table or desk.
Screens with mesh designed to keep mosquitoes out should be used in every window and placed across every opening to the outdoors. Screen doors should be used at all times. Air conditioning, where available, will slow or stop mosquito activity.
These mosquito species breed in fresh water left after a rain. Puddles in ditches, unused birdbaths, poorly draining gutters and discarded tires are perfect breeding sites for these pests. Proper sanitary practices include removing or draining all potential breeding sites. Mosquitoes rarely fly more than a few hundred yards in their lives so cleaning up the yard, nearby vacant lots, rooftops and the like can go a long way to reducing the mosquito population in the vicinity.
Use insect repellants containing DEET, picaridin, IR3535, oil of lemon eucalyptus and para-menthane-diol. Wear long sleeves and long pant when outside and treat clothing with permethrin or purchase permethrin-treated clothing.
If you become infected with chikungunya, you can infect mosquitoes. It is important to avoid bites during the first week of illness to prevent spreading the illness to other people.
Four cases of chikungunya have been diagnosed in the U.S. thus far. All were contracted in the Caribbean. Locally acquired cases of the illness may appear at any time and will almost certainly be found before the end of the summer in places such as Florida. If you should fall ill with “the summer flu”, call your doctor at once.