Chikungunya

Introduction

Infectious agent

Chikungunya virus is a single-stranded RNA virus that belongs to the familyTogaviridae, genus Alphavirus.

Transmission

Chikungunya virus is transmitted to humans via the bite of an infected mosquito of the Aedes spp., predominantly Aedes aegypti and Aedes albopictus. Related Aedes spp. mosquitoes present primarily in the forest or jungle can also transmit the virus. Mosquitoes become infected when they feed on viremic humans or non-human primates, both of which are likely the main amplifying reservoirs of the virus. Humans are typically viremic shortly before and in the first 6 days of illness.

Blood-borne transmission is possible; one case has been documented in a healthcare professional who was exposed to 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 but is rare in most stages of pregnancy. The greatest risk occurs in the perinatal period, when the pregnant woman is viremic at the time of delivery, with transmission occurring in up to 50% of cases often causing severe neonatal disease (see Clinical presentation section). Although chikungunya viral RNA has been identified in the breast milk of several women living in an endemic area, attempts to recover intact virus have been unsuccessful. In addition, for the one breastfed infant who was reportedly exposed to milk with chikungunya viral RNA, the infant had no symptoms or evidence of infection based on laboratory testing. Chikungunya viral RNA has been identified in semen, but no evidence of sexual transmission has been identified to date.

Epidemiology

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, the Americas, and Asia. Recent large outbreaks include Ethiopia in 2019 and Paraguay in 2023, with over 50,000 and 160,000 suspected cases, respectively.

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, when 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.

After the outbreaks in the Americas during 2014–2017, >4,000 chikungunya cases were reported among U.S. travelers, and 13 locally acquired cases were reported in the continental United States. In addition, the U.S. territories of American Samoa, U.S. Virgin Islands, and Puerto Rico reported locally acquired cases during 2014–2015. During 2018–2023, 612 U.S. traveler cases were reported, with noticeably fewer cases during 2020–2021 because of decreases in international travel during the COVID-19 pandemic.

Clinical presentation

Both adults and children can become infected and be symptomatic with chikungunya. Approximately 15%–35% 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 39°C [>102°F]) 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 morbilliform (e.g., maculopapular) and often pruritic, 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 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 and by mosquito bites after birth, adults aged >65 years, 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 continuation or 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 illness. Deaths associated with infection occur but are rare and are reported most commonly in older adults with comorbidities and young infants infected perinatally or by mosquito bites.

Women 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. However, intrapartum transmission can result in neonatal complications, including hemorrhagic symptoms, myocardial disease, and neurologic disease. Rare spontaneous abortions after first-trimester maternal infection have been reported.

Diagnosis

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 adenoviral infection, other alphaviral diseases (Barmah Forest, Mayaro, o'nyong-nyong, Ross River, and Sindbis), dengue, enteroviral disease, leptospirosis, malaria, measles, Oropouche, parvovirus infection, rubella, group A Streptococcus infection, typhus, Zika, and postinfectious arthritis and rheumatologic conditions.

Laboratory diagnosis is generally accomplished by testing serum to detect virus, viral nucleic acid, virus-specific IgM, or neutralizing antibodies. Because infected individuals develop 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) or non-specific antibodies. Plaque reduction neutralization tests can be used to confirm the infection and, if warranted, discriminate between cross-reacting or non-specific 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 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.

Treatment

No specific antiviral treatment is available for chikungunya, although several therapeutic options are being investigated. Treatment for symptoms includes rest, fluids, and use of analgesics and antipyretics. Nonsteroidal anti-inflammatory drugs can be used to help with acute fever and pain. However, for patients who report travel to dengue-endemic areas, acetaminophen or paracetamol 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, nonsteroidal anti-inflammatory drugs, corticosteroids, including topical preparations, and physical therapy might help lessen the symptoms.

Prevention

Travelers at increased risk for more severe disease, including travelers with underlying medical conditions and women 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 (e.g., vaccination or avoiding mosquito bites).

Personal protective measures

The best way to prevent mosquito-borne diseases, including chikungunya, is to avoid mosquito bites (see Mosquitoes, Ticks, and Other Arthropods chapter).

Vaccine

In 2023, the U.S. Food and Drug Administration (FDA) approved a chikungunya vaccine, IXCHIQ (manufactured by Valneva), for adults aged 18 years and older (Table 4.1.1). In 2024, the U.S. Advisory Committee on Immunization Practices (ACIP) approved recommendations for use of the vaccine among certain travelers.

See CDC's Chikungunya website for information on groups for whom vaccination is recommended and may be considered, and information on recent chikungunya virus transmission. Future availability of IXCHIQ for adolescents and children is expected. In addition to IXCHIQ, a virus-like particle vaccine manufactured by Bavarian Nordic has been submitted to FDA for licensure. Other candidate vaccines are in development.

Safety and adverse reactions

Common adverse reactions following vaccination with IXCHIQ that occurred in >10% of vaccinated persons in clinical trials included injection site tenderness, headache, fatigue, myalgia, arthralgia, fever, and nausea. IXCHIQ also caused severe or prolonged chikungunya-like adverse reactions in some persons.

Precautions and contraindications

Contraindications to the use of IXCHIQ include immunocompromising conditions (due to immunodeficiencies or immunosuppressive and immunomodulatory therapies) or a history of a severe allergic reaction (e.g., anaphylaxis) to any component of the vaccine.

Precautions for the use of IXCHIQ include pregnancy or breastfeeding. More information on the use of IXCHIQ in pregnant and breastfeeding women can be found on CDC's Chikungunya Vaccine website.

Table 4.1.1: Vaccine to prevent chikungunya