Last December, the World Health Organization (WHO) reported the first local transmission of chikungunya virus in St. Martin (French West Indies) in the Caribbean. Previously, chikunguna virus had occurred only in travelers returning from endemic areas. Local transmission has since been reported in at least 24 other Caribbean countries, including Aruba, the Bahamas, the Cayman Islands, Jamaica, Puerto Rico, and the U.S. Virgin Islands. Now cases are popping up in the U.S. Worthy of note: One of them appears to be a case acquired locally on the U.S.
Chikungunya is primarily a mosquito-borne alphavirus, although bloodborne transmission has been documented among laboratory personnel who handled infected blood. Previous outbreaks have occurred in Africa, Southern Europe, Southeast Asia, the Indian subcontinent, and islands in the Indian and Pacific Oceans.
The number of cases of chikungunya virus infection has increased significantly since the beginning of this year, spiraling up to more than half a million. Last June, a number of cases were reported in North Carolina, Florida, Mississippi, Georgia, Arkansas—all contracted by people who had traveled in infected countries. Then, in July, the first case of chikungunya acquired in the U.S. was reported in Florida. This is the first time the disease was transmitted by mosquitoes on the U.S. mainland.
Risks and Symptoms
Anyone traveling to an infected area is at risk of being bitten by infected mosquitoes. Those with medical conditions—such as arthritis, hypertension, cardiovascular disease, or diabetes—or anyone over age 65 are at higher risk for contracting the virus. Most people who are infected become symptomatic after an incubation period that ranges from 3 to 7 days. Symptoms are similar to dengue fever, another mosquito-borne tropical disease, and include fever, severe joint pain, headache, myalgia, arthritis, and rash. Clinicians should consider chikungunya virus as a possible diagnosis in patients who exhibit these symptoms and who have recently traveled to the Caribbean. Any suspected chikungunya cases should be reported to state or local health department authorities.
Diagnosis and Treatment
Blood tests to detect virus, viral nucleic acid, or virus-specific immunoglobulin M (IgM) and neutralizing antibodies can identify chikungunya virus. Diagnostic testing is performed only at the Centers for Disease Control (CDC), two state health departments (California and New York), and one commercial laboratory, so health care providers should contact their state or local health department to determine where to send samples. In most cases, test results are available within 4 to 14 days. Any patient who is suspected of being infected with chikungunya virus should also be evaluated for dengue virus infection because both viruses are prevalent in the same geographic areas and produce similar symptoms.
There is no specific antiviral therapy for chikungunya virus. Treatment focuses on relieving symptoms and includes rest, fluids, and nonsteroidal anti-inflammatory drugs (NSAIDs) to relieve joint pain and fever. Anyone is who infected with chikungunya virus should be protected from further mosquito exposure during the first few days of illness to reduce the risk of local transmission because other mosquitoes can become infected after biting an infected human.
Chikungunya virus is rarely fatal, but it can be severe and disabling. Most patients begin to improve within 10 days, although joint pain can persist for several months. Complications can include uveitis, retinitis, myocarditis, hepatitis, nephritis, bullous skin lesions, hemorrhage, meningoencephalitis, myelitis, Guillain-Barré syndrome, and cranial nerve palsies, but all of these are rare.
There is currently no vaccine or medication that prevents chikungunya. The CDC recommends that anyone who travels to an area where mosquitoes are known to be infected take protective measures to avoid mosquito bites by using insect repellent products containing DEET, picaridin, or oil of lemon eucalyptus; wearing protective clothing (ideally clothing that is treated with permethrin); and staying in air conditioned areas or areas that are protected by window and door screens.
More information about chikungunya virus is available through the CDC.