CDC Yellow Book 2024Travel-Associated Infections & Diseases
INFECTIOUS AGENT: Chikungunya virus
Tropical and subtropical regions worldwide
TRAVELER CATEGORIES AT GREATEST RISK FOR EXPOSURE & INFECTION
Avoid insect bites
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. Mosquitoes become infected when they feed on viremic nonhuman or human primates, both of which are likely the main amplifying reservoirs of the virus. Humans are typically viremic shortly before and in the first 2–6 days of illness.
Bloodborne transmission is possible; 1 case has been documented in a health care worker who sustained a needle stick after drawing blood from an infected patient. Furthermore, chikungunya virus has been identified in donated blood products undergoing screening, although no transfusion-associated cases have been identified to date. Cases also have been documented among laboratory personnel handling infected blood, through percutaneous punctures, and through aerosol exposure in the laboratory.
Maternal–fetal transmission has been documented during pregnancy; the greatest risk occurs in the perinatal period when the pregnant person is viremic at the time of delivery. Although chikungunya viral RNA was identified in the breast milk of 1 infected person, the breastfed infant had no symptoms or evidence of infection based on laboratory testing. Additionally, chikungunya viral RNA has been identified in semen, but no evidence of sexual transmission has been noted to date.
Chikungunya virus occurs in tropical and subtropical regions. It often causes large outbreaks with high attack rates, affecting up to 75% of the population in areas where the virus is circulating. Outbreaks of chikungunya have occurred in Africa, the Americas, 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 2017, >2.6 million suspected cases of chikungunya had been reported in the Americas. Since then, the virus has continued to circulate and cause sporadic cases and periodic outbreaks in many areas of the world, including Africa, South America, and Asia.
Risk to travelers is greatest in areas experiencing ongoing chikungunya epidemics. Most epidemics occur during the tropical rainy season and abate during the dry season. Outbreaks in Africa have occurred after periods of drought, however, where open water containers near human habitats served as vector-breeding sites. Risk for infection exists primarily during the day, because the primary vector, Ae. aegypti, aggressively bites during daytime. Ae. aegypti mosquitoes bite indoors or outdoors near dwellings and lay their eggs in domestic containers that hold water, including buckets and flowerpots.
Both adults and children can become infected and be symptomatic with chikungunya. After the outbreaks in the Americas during 2014–2017, >4,000 chikungunya cases were reported among US travelers, and 13 locally acquired cases were reported in the continental United States. In addition, the US territories of American Samoa, US Virgin Islands, and Puerto Rico reported locally acquired cases during 2014–2015; Puerto Rico also has been reporting sporadic cases since 2016. During 2018–2020, 340 US traveler cases were reported, with noticeably fewer cases in 2020 due to decreases in international travel during the coronavirus disease 2019 (COVID-19) pandemic.
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. Fevers typically last for ≤1 week; the fever can be biphasic. Joint symptoms are typically severe, can be debilitating, and usually involve multiple joints, typically bilateral and symmetric. Joint pain occurs most commonly in hands and feet but can affect more proximal joints. Other symptoms include conjunctivitis, headache, myalgia, nausea, vomiting, or a rash. The rash, which is typically maculopapular, occurs after onset of fever and involves the trunk and extremities but also can include the palms, soles, and face.
Abnormal laboratory findings can include elevated creatinine and liver function tests, lymphopenia, and thrombocytopenia. Rare but serious complications of the disease include hepatitis, myocarditis, neurologic disease (cranial nerve palsies, Guillain-Barré syndrome, meningoencephalitis, myelitis), ocular disease (uveitis, retinitis), acute renal disease, and severe bullous skin lesions. 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 (e.g., diabetes, heart disease, hypertension).
Acute symptoms of chikungunya typically resolve in 7–10 days. Some patients will have a relapse of rheumatologic symptoms (e.g., polyarthralgia, polyarthritis, tenosynovitis, Raynaud syndrome) in the months after acute illness. Studies have reported variable proportions, ranging from 5% to 80%, of patients with persistent joint pains, and prolonged fatigue, for months or years after their illness. Fatalities associated with infection occur but are rare and are reported most commonly in older adults and those with comorbidities.
People who are pregnant 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. Intrapartum transmission can, however, result in neonatal complications, including hemorrhagic symptoms, myocardial disease, and neurologic disease. Rare spontaneous abortions after first-trimester maternal infection have been reported.
The differential diagnosis of chikungunya virus infection depends on clinical features (signs and symptoms) and when and where the person was suspected of being infected. Consider other infections and diseases in the differential diagnosis, including adenovirus, other alphaviruses (Barmah Forest, Mayaro, O’nyong-nyong, Ross River, and Sindbis), dengue, enterovirus, leptospirosis, malaria, measles, parvovirus, rubella, group A Streptococcus, typhus, Zika, and postinfectious arthritis and rheumatologic conditions.
Laboratory diagnosis is generally accomplished by testing serum to detect virus, viral nucleic acid, or virus-specific IgM and neutralizing antibodies. Because the virus develops high levels of viremia during the first week after symptom onset, chikungunya can often be diagnosed by performing viral culture or nucleic acid amplification on serum. Virus-specific IgM antibodies normally develop toward the end of the first week of illness but can remain detectable for months to years after infection. Rarely, serum IgM antibody testing can yield false-positive results due to cross-reacting antibodies against related alphaviruses (e.g., Mayaro virus, O’nyong-nyong virus). Plaque reduction neutralization tests (PRNT) can be used to confirm the infection and, if warranted, discriminate between cross-reacting antibodies.
Testing for chikungunya virus infection is performed at several state health department laboratories and commercial laboratories. Confirmatory testing for virus-specific neutralizing antibodies is available through the Centers for Disease Control and Prevention (CDC)’s Division of Vector-Borne Diseases (970-221-6400). Report suspected chikungunya cases to state or local health departments to facilitate diagnosis and mitigate the risk for 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; a number of therapeutic options are being investigated, however. Treatment for symptoms include rest, fluids, and use of analgesics and antipyretics. Nonsteroidal anti-inflammatory drugs can be used to help with acute fever and pain. For patients who report travel to dengue-endemic areas, however, acetaminophen is the preferred first-line treatment for fever and joint pain to reduce the risk for hemorrhage until dengue can be ruled out. For patients with persistent joint pain, use of nonsteroidal anti-inflammatory drugs, corticosteroids, including topical preparations, and physical therapy might help lessen the symptoms.
Currently, no vaccine or preventive drug is available; several candidate vaccines are in various stages of development. Travelers can best prevent infection by avoiding mosquito bites (see Sec. 4, Ch. 6, Mosquitoes, Ticks & Other Arthropods). Travelers at increased risk for more severe disease, including travelers with underlying medical conditions and people late in their pregnancy (because their fetuses are at increased risk), might consider avoiding travel to areas with ongoing chikungunya outbreaks. If travel is unavoidable, emphasize the importance of using protective measures against mosquito bites.
CDC website: www.cdc.gov/chikungunya
The following authors contributed to the previous version of this chapter: J. Erin Staples, Susan L. Hills, Ann M. Powers
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