Chikungunya virus is a single-stranded RNA virus that belongs to the family Togaviridae, genus Alphavirus .
Chikungunya virus is transmitted to humans via the bite of an infected mosquito of the Aedes spp., predominantly Aedes aegypti and Ae. albopictus . Nonhuman and human primates are likely the main reservoirs of the virus, and human-to-vector-to-human transmission occurs during outbreaks of the disease. Bloodborne transmission is possible; 1 case was documented in a health care worker who was stuck with a needle after drawing blood from an infected patient. Cases have also been documented among laboratory personnel handling infected blood and through aerosol exposure in the laboratory.
The risk of a person transmitting the virus to a biting mosquito or through blood is highest when the patient is viremic, usually during the first 2–6 days of illness. Maternal-fetal transmission has been documented during pregnancy; the highest risk occurs when a woman is viremic at the time of delivery. Studies have not found virus in breast milk.
Chikungunya virus often causes large outbreaks with high attack rates, affecting one-third to three-quarters of the population in areas where the virus is circulating. Outbreaks of chikungunya have occurred in Africa, Asia, Europe, and islands in the Indian and Pacific Oceans. In late 2013, the first locally acquired cases of chikungunya were reported in the Americas on islands in the Caribbean. By the end of 2014, more than 1.1 million suspect cases of chikungunya had been reported in the Americas. Since then the virus has continued to circulate and cause disease in the Americas, Southeast Asia, Pacific Islands, and Africa.
Risk to travelers is highest in areas experiencing ongoing epidemics of the disease (for the most updated information see the Travel Health Notices section on the CDC Travelers’ Health website at wwwnc.cdc.gov/travel/notices). Most epidemics occur during the tropical rainy season and abate during the dry season. However, outbreaks in Africa have occurred after periods of drought, where open water containers in close proximity to human habitation served as vector-breeding sites. Risk of infection exists throughout the day, as the primary vector, Ae. aegypti , aggressively bites during the daytime. Ae. aegypti mosquitoes bite indoors or outdoors near a dwelling. They typically breed in domestic containers that hold water, including buckets and flower pots.
Both adults and children can become infected and symptomatic with the disease. From 2010 through 2013, 110 cases of chikungunya were identified or reported among US travelers who predominantly traveled to areas with known ongoing outbreaks. Following the outbreaks in the Americas, however, >3,500 chikungunya cases have been reported from US states through the end of April 2016. Although most were in travelers, a few cases acquired locally in the continental United States were reported in 2014 and 2015. In addition, several US territories (Puerto Rico, US Virgin Islands, and American Samoa) have reported locally acquired cases from 2014–2016.
Approximately 3%–28% of people infected with chikungunya virus will remain asymptomatic. For people who develop symptomatic illness, the incubation period is typically 3–7 days (range, 1–12 days). Disease is most often characterized by sudden onset of high fever (temperature typically >102°F [39°C]) and joint pains. Other symptoms may include headache, myalgia, arthritis, conjunctivitis, nausea, vomiting, or a maculopapular rash. Fevers typically last from several days up to 1 week; the fever can be biphasic. Joint symptoms are often severe and can be debilitating. They usually involve multiple joints, typically bilateral and symmetric. They occur most commonly in hands and feet, but they can affect more proximal joints. Rash usually occurs after onset of fever. It typically involves the trunk and extremities but can also include the palms, soles, and face.
Abnormal laboratory findings can include thrombocytopenia, lymphopenia, and elevated creatinine and liver function tests. Rare but serious complications of the disease can occur, including myocarditis, ocular disease (uveitis, retinitis), hepatitis, acute renal disease, severe bullous lesions, and neurologic disease, such as meningoencephalitis, Guillain-Barré syndrome, myelitis, or cranial nerve palsies. Groups identified as having increased risk for more severe disease include neonates exposed intrapartum, adults >65 years of age, and people with underlying medical conditions, such as hypertension, diabetes, or heart disease.
Acute symptoms of chikungunya typically resolve in 7–10 days. Fatalities associated with infection occur but are typically rare and most commonly reported in older adults. Some patients will have a relapse of rheumatologic symptoms such as polyarthralgia, polyarthritis, tenosynovitis, or Raynaud syndrome in the months after acute illness. Studies have reported variable proportions, ranging from 5% to 80%, of patients with persistent joint pains for months or years after their illness.
Pregnant women have symptoms and outcomes similar to those of other people, and most infections that occur during pregnancy will not result in the virus being transmitted to the fetus. However, when intrapartum transmission occurs, it can result in complications for the baby, including neurologic disease, hemorrhagic symptoms, and myocardial disease. There are also rare reports of spontaneous abortions after maternal infection during the first trimester.
The differential diagnosis of chikungunya virus infection depends on the clinical signs and symptoms as well as where the person was suspected of being infected. Diseases that should be considered in the differential diagnosis include dengue, Zika, malaria, leptospirosis, parvovirus, enterovirus, group A Streptococcus , rubella, measles, adenovirus, postinfectious arthritis, rheumatologic conditions, or alphavirus infections (including Mayaro, Ross River, Barmah Forest, O’nyong-nyong, and Sindbis viruses).
Preliminary diagnosis is based on the patient’s clinical features, places and dates of travel, and activities. Laboratory diagnosis is generally accomplished by testing serum to detect virus, viral nucleic acid, or virus-specific IgM and neutralizing antibodies. During the first week after onset of symptoms, chikungunya can often be diagnosed by performing viral culture or nucleic acid amplification on serum. Virus-specific IgM and neutralizing antibodies normally develop toward the end of the first week of illness. Therefore, to definitively rule out the diagnosis, convalescent-phase samples should be obtained from patients whose acute-phase samples test negative.
Testing for chikungunya virus is performed at CDC, several state health department laboratories, and several commercial laboratories. Health care providers should report suspected chikungunya cases to their state or local health departments to facilitate diagnosis and mitigate the risk of local transmission. Because chikungunya is a nationally notifiable disease, state health departments should report laboratory-confirmed cases to CDC through ArboNET, the national surveillance system for arboviral diseases.
No specific antiviral treatment is available for chikungunya. Treatment is for symptoms and can include rest, fluids, and use of analgesics and antipyretics. Nonsteroidal anti-inflammatory drugs can be used to help with acute fever and pain. In dengue-endemic areas, however, acetaminophen is the preferred first-line treatment for fever and joint pain until dengue can be ruled out, to reduce the risk of hemorrhage. For patients with persistent joint pain, use of nonsteroidal anti-inflammatory drugs, corticosteroids including topical preparations, and physical therapy may help lessen the symptoms.
No vaccine or preventive drug is available. The best way to prevent infection is to avoid mosquito bites (see Chapter 2, Protection against Mosquitoes, Ticks, & Other Arthropods). Travelers at increased risk for more severe disease, including travelers with underlying medical conditions and women who are late in their pregnancy (as their unborn infants are at increased risk), may consider avoiding travel to areas with ongoing outbreaks. If travel is unavoidable, emphasize the need for protective measures against mosquito bites.
CDC website: www.cdc.gov/chikungunya
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J. Erin Staples, Susan L. Hills, Ann M. Powers