Chikungunya virus

Chikungunya virus is a mosquito-borne alphavirus and the most important cause of epidemic viral arthritis. Its hallmark is an abrupt febrile illness with severe, frequently incapacitating joint pain, from which a large minority of patients go on to months or years of relapsing arthritis. First recognised in East Africa in the 1950s, it has since produced some of the largest arbovirus epidemics on record: across the Indian Ocean and Asia from 2004, throughout the Americas from 2013, and in a renewed global wave in 2025 that reached temperate Europe and drove the largest outbreak yet seen in China. It shares its urban Aedes vectors and its clinical stage with dengue and Zika, and the three are constantly confused at the bedside. Two vaccines have now been licensed, the first ever against the disease, although the safety of the live-attenuated product has become a live regulatory question. For most of its history the virus had no specific treatment and none exists now: care is supportive and prevention rests on the mosquito.

Discovery and historical significance

An epidemic of sudden, crippling joint pain swept the Makonde Plateau of southern Tanganyika, now Tanzania, in 1952. The name chikungunya derives from a Makonde word describing the contorted, stooped posture forced by the arthritis, and the virus was isolated from patient serum and from mosquitoes over the following two years, one of the group A arboviruses that would later be organised into the genus Alphavirus. Retrospective study of clinical records suggests that epidemics compatible with chikungunya, long confused with dengue, had occurred for at least two centuries before.

For decades the virus was regarded as a cause of self-limited African and Asian outbreaks. That view changed in 2004, when an epidemic beginning in coastal Kenya spread across the islands of the Indian Ocean and into India and Southeast Asia, infecting millions and, on the island of Réunion, a mutation in the virus that adapted it to a new mosquito. The arrival of the virus in the Caribbean in 2013 and its rapid spread through the Americas confirmed its standing as a pandemic-capable pathogen rather than a regional curiosity.

Classification, structure, and genome

Classification

Chikungunya virus is the species Alphavirus chikungunya in the genus Alphavirus, family Togaviridae. It belongs to the Semliki Forest antigenic complex and is closely related to o’nyong-nyong virus, which it resembles clinically. Within the genus it is one of the Old World arthritogenic alphaviruses, whose disease is fever, rash and polyarthritis, as distinct from the New World alphaviruses that cause encephalitis. This split of the genus into Old World arthritogenic and New World encephalitic agents is the classical and predominant pattern rather than an absolute rule: chikungunya itself can occasionally cause meningoencephalitis, and the encephalitic viruses often produce a systemic febrile illness.

Alphaviruses of the genus Alphavirus by disease type

Group	Geographic origin	Representative viruses	Typical human disease
Old World arthritogenic	Africa, Asia, Australasia	Chikungunya, Sindbis, o’nyong-nyong, Ross River, Semliki Forest, Barmah Forest	Fever, rash, polyarthralgia
New World encephalitic	The Americas	Eastern, Western and Venezuelan equine encephalitis viruses	Febrile illness, encephalitis
Exception	The Americas	Mayaro	Arthritogenic despite New World origin

Four lineages are recognised. Two are enzootic African lineages, the West African and the East, Central and South African (ECSA); from the ECSA lineage arose the Indian Ocean Lineage that drove the 2004 to 2007 epidemic, while an older Asian lineage seeded the American outbreaks.

Virion structure

The virion is an enveloped, roughly spherical particle about 70 nm across, sensitive to detergents and lipid solvents. A single capsid protein forms an icosahedral nucleocapsid, on a triangulation number of 4, that encloses the RNA genome. The host-derived lipid envelope carries 80 glycoprotein spikes, each a trimer of paired E1 and E2 heterodimers. E2 is the attachment protein and the dominant target of neutralising antibody, while E1, more conserved across the genus, carries the internal fusion peptide that drives membrane fusion. A small E3 glycoprotein chaperones the E2 precursor and is removed by the host protease furin during maturation.

Genome organisation

The genome is a single molecule of positive-sense, single-stranded RNA of about 11.8 kilobases, capped and polyadenylated, and infectious on its own. Its 5’ two-thirds encodes the four nonstructural proteins, nsP1 to nsP4, translated directly as a polyprotein; the structural proteins are translated from a separate subgenomic messenger RNA. nsP4 is the RNA-dependent RNA polymerase, nsP1 caps the viral RNA and anchors the replication complex to membranes, nsP2 is the protease and helicase that also helps shut off host transcription, and nsP3 is a virulence and host-range determinant that recruits host proteins to the replication complex.

Replication cycle

Attachment is mediated by the E2 glycoprotein. Alphaviruses use several receptors and attachment factors, which underpins their broad host range, but for the arthritogenic viruses including chikungunya the cell-adhesion molecule MXRA8 is a key entry receptor, engaging the E1 and E2 spike and helping to explain the virus’s tropism for joint and muscle tissue. After binding, the particle is taken up by clathrin-mediated endocytosis.

The acid environment of the endosome triggers the fusion cascade. E1 dissociates from E2, inserts its fusion peptide into the endosomal membrane and folds back into a stable trimer, merging the two membranes and delivering the nucleocapsid to the cytoplasm. The incoming genome is translated into the nonstructural polyprotein, which is processed in a set order by the nsP2 protease; the early, uncleaved complex synthesises a minus-strand template, and the later, fully processed complex switches to making abundant plus-strand genomes and the subgenomic RNA.

The subgenomic RNA is translated into the structural polyprotein, from which capsid protein cleaves itself and binds new genomes into nucleocapsids in the cytoplasm, while the E1 and E2 glycoproteins mature through the secretory pathway to the cell surface. Assembly is completed as nucleocapsids engage the glycoprotein tails and bud through the plasma membrane, a rapid cycle that releases progeny within hours and kills the vertebrate cell over a day or two.

Pathogenesis

Mosquito saliva deposits virus into the skin, where it first replicates in fibroblasts and is carried by dendritic cells to the draining lymph node and thence to the blood. Viraemia is high, often exceeding a million infectious units per millilitre, and its magnitude tracks the severity of illness and the strength of the interferon response it provokes. From the blood the virus seeds its target tissues: joint, muscle, skin, and less often liver, heart and brain.

The joint is the defining site of disease. The virus infects synovial fibroblasts and tissue macrophages, and although infectious virus is seldom recovered from joint fluid, viral RNA and antigen persist in synovium after the blood has cleared. This persistence sustains a local inflammatory response, with perivascular macrophage infiltration, synovial hyperplasia, activated natural killer (NK) cells and CD4 T cells, and high tissue levels of interleukin-6 and granulocyte-macrophage colony-stimulating factor, the mechanism thought to drive the chronic arthralgia. Infection of bone-lining osteoblasts, tipping the balance of bone remodelling toward resorption, may add a destructive element in a minority.

Recovery depends chiefly on antibody. IgM appears within a few days and IgG within one to two weeks, and neutralising antibody to E2 confers durable, probably lifelong, immunity to reinfection. Adaptation to the vector has shaped the virus’s spread: the E1-A226V substitution acquired during the Indian Ocean epidemic allowed efficient transmission by Aedes albopictus, a hardier, more temperate mosquito than Aedes aegypti, extending the virus’s potential range into cooler regions.

Epidemiology

Chikungunya virus is transmitted between people by two urban mosquitoes, Aedes aegypti and Aedes albopictus, in a human-mosquito-human cycle that needs no animal reservoir to sustain an epidemic; an ancestral African sylvatic cycle involves forest Aedes species and non-human primates. Because humans develop high viraemia, a single imported case can seed local transmission wherever a competent vector is present, and outbreaks are explosive, with attack rates in a susceptible population that can approach a third or more.

The modern history is one of expanding waves. The 2004 to 2007 Indian Ocean epidemic infected roughly a third of the population of Réunion, some 300,000 people, and spread to India and Southeast Asia; the virus reached the Caribbean in 2013 and swept the Americas over the following years, causing millions of cases in populations with no prior immunity. In 2025 the virus resurged worldwide: the World Health Organization reported more than 440,000 cases across some 40 countries in the first nine months of the year, with a major recurrence on Réunion affecting about a third of the island again and the largest outbreak ever recorded in China, centred on Foshan in Guangdong Province. Autochthonous transmission in southern Europe, seeded by viraemic travellers and sustained by established Aedes albopictus, has become a recurring summer event.

Natural history

After an incubation of two to twelve days, most often three to seven, the illness begins abruptly, without a prodrome. Most infections are symptomatic, in contrast to dengue and Zika, though up to a quarter are subclinical or asymptomatic. The acute phase is dominated by high fever and severe joint pain that peak over the first few days and settle in most people within one to two weeks. Viraemia is present from around the onset of symptoms and lasts about a week, the window in which the patient is infectious to feeding mosquitoes.

Resolution of the acute illness is not always the end. A substantial proportion of patients enter a subacute or chronic phase in which joint pain and stiffness relapse or simply fail to remit, sometimes for months and occasionally for years. Older age, female sex, more severe acute disease and higher acute viral load all predict this outcome, whereas radiographs usually show only soft-tissue swelling rather than joint destruction. Whatever its course, an episode of infection is followed by durable, probably lifelong immunity to reinfection.

Clinical presentations and complications

Acute chikungunya fever

The classic triad is fever, arthralgia and rash. Fever is high, often 39 to 40 degrees Celsius, and the joint pain is severe, symmetrical and frequently incapacitating, affecting the small joints of the hands and feet, the wrists and the ankles, with swelling, stiffness worse in the morning, and sometimes tenosynovitis. A maculopapular, often itchy rash appears in around 80% of patients a few days into the illness, typically over the trunk and limbs and sometimes the face, and lasts a few days. Headache, myalgia, conjunctival injection and gastrointestinal upset are common accompaniments.

Chronic arthritis

The most important sequela is persistent inflammatory arthralgia. Recurrent or unremitting joint symptoms affect on the order of 40% of adults in the years after infection, more often women and older patients, and can resemble a seronegative inflammatory arthritis in distribution and impact. The pain and stiffness may be genuinely disabling and are a substantial source of the epidemic’s economic and quality-of-life burden, even though frank joint erosion is uncommon.

Severe and atypical disease

Severe disease is uncommon, of the order of a fraction of a percent of cases, but the spectrum is broad: encephalitis and encephalopathy, myocarditis, hepatitis, nephritis, bullous skin disease and thrombocytopenia. Neuroinvasive disease is more frequent than with the other arthritogenic alphaviruses, and the overall case-fatality is low, around one per thousand, concentrated in neonates, the elderly and those with comorbidities. A distinct and serious problem is vertical transmission: a mother who is viraemic around the time of delivery can pass the virus to her newborn in roughly half of cases, causing a severe neonatal illness with encephalopathy and a real risk of long-term neurological harm.

Diagnosis

The diagnostic approach follows the viraemia. In the first week of illness, reverse-transcription PCR on blood is the test of choice, detecting viral RNA during the high-titre viraemic phase, after which its yield falls. From about day five, as viraemia wanes, IgM becomes detectable by enzyme immunoassay and persists for weeks to months; a rising titre or seroconversion on paired sera confirms recent infection, and neutralisation assays resolve cross-reactivity within the genus.

The central practical task is to distinguish chikungunya from the other arboviruses that share its vector and setting. Dengue and Zika cause overlapping febrile illness but favour myalgia over the prominent, persistent arthralgia of chikungunya, and dengue carries the added risks of haemorrhage and shock that make it the more urgent to exclude. In Africa, o’nyong-nyong virus produces a near-identical syndrome and is separated serologically, aided by its characteristic prominent cervical lymphadenopathy.

Management

There is no licensed antiviral for chikungunya, and treatment is supportive. Acute care rests on rest, fluids and analgesia, with paracetamol preferred until dengue has been excluded because non-steroidal anti-inflammatory drugs and aspirin carry bleeding and other risks in dengue; once dengue is excluded, non-steroidal anti-inflammatory drugs are the mainstay for the arthralgia. Corticosteroids are generally avoided in the acute phase.

Persistent arthritis is managed as an inflammatory arthropathy. Most cases respond to non-steroidal anti-inflammatory drugs and physiotherapy, but refractory or erosive disease may warrant a short course of corticosteroids or, occasionally, disease-modifying antirheumatic drugs such as methotrexate under specialist care. Recovery is the rule even in prolonged cases, and reassurance about the eventual outcome is part of management.

Prevention and public health

Vector control

Because transmission depends on urban Aedes mosquitoes, personal protection and vector control are the practical foundation of prevention. Bite avoidance with repellents, protective clothing and insecticide-treated materials, together with elimination of the domestic water containers in which Aedes aegypti breeds, are the mainstay, supported during outbreaks by larviciding, targeted adulticiding and community source reduction. Novel Aedes-suppression approaches, including Wolbachia-based and sterile-insect methods, are being deployed against the same vectors that transmit dengue and Zika. A viraemic patient should avoid further mosquito bites during the first week to interrupt onward transmission.

Vaccination

The chikungunya vaccine landscape was revolutionised in late 2023 with the landmark approval of Ixchiq, the world’s first live-attenuated vaccine for adults. Developed by Valneva, it paved the way for subsequent approvals like Vimkunya in Europe, targeting travellers and endemic populations.

While approved in Western markets, global availability remains fragmented; Valneva voluntarily withdrew Ixchiq from the US market in early 2026 following safety reviews regarding adverse events in elderly individuals. Today, routine access is limited in highly endemic countries, though Brazil has initiated targeted pilot rollouts.

The field is moving quickly, and any recommendation on chikungunya vaccination should be checked against current regulatory and national guidance.

Surveillance and notification

Chikungunya is a target of arbovirus surveillance in most endemic and at-risk countries, reported through case-based systems that also track dengue and Zika, so that the appearance of a locally acquired case can trigger vector control before an outbreak establishes. Laboratory-confirmed cases are notifiable in many jurisdictions, and travel-associated cases are watched closely in regions where Aedes albopictus could sustain local transmission.

South African context

Chikungunya is not endemic in South Africa in the way it is in tropical Africa and Asia, and most South African cases are imported by travellers returning from endemic regions. The risk is nonetheless real because the principal urban vector, Aedes aegypti, is present in parts of the country, so an imported viraemic case can in principle seed local transmission, and the National Institute for Communicable Diseases conducts arbovirus surveillance that covers chikungunya alongside dengue, Zika and the locally important arboviruses. Chikungunya sits within the differential diagnosis of fever with arthralgia and rash in a returning traveller, to be distinguished from dengue and from the endemic South African alphavirus Sindbis.

South African clinical research has contributed to the understanding of the disease’s chronic phase. A South African follow-up cohort found that although about a third of patients recovered within weeks, a third took around a year to resolve and roughly one in seven remained symptomatic for two to three years, with younger patients recovering fastest, illustrating the substantial and prolonged musculoskeletal burden that follows the acute illness.

References and recommended reading

• Griffin DE, Weaver SC. Alphaviruses. In: Fields Virology, 7th edition. Philadelphia: Wolters Kluwer; 2023. The principal reference for the classification, virion structure, genome, replication cycle and pathogenesis set out here.
• Smith DW, Mackenzie JS, Frolov IV, Weaver SC. Alphaviruses. In: Richman DD, Whitley RJ, Hayden FG (eds.), Clinical Virology, 4th edition. Washington: ASM Press; 2016. The source for the clinical spectrum, chronic arthritis, diagnostic approach and the South African chronic-disease cohort.
• Burrell CJ, Howard CR, Murphy FA. Togaviruses. In: Fenner and White’s Medical Virology, 5th edition. London: Academic Press / Elsevier; 2017. A concise account of alphavirus biology and epidemiology.
• World Health Organization. Chikungunya (fact sheet and 2025 global situation reports). Geneva: World Health Organization; 2025. The source for the current global epidemiology, including the 2025 resurgence.
• Staples JE, Hills SL, Powers AM. Chikungunya. In: CDC Yellow Book 2026: Health Information for International Travel. Atlanta: Centers for Disease Control and Prevention; 2025. The source for the current vaccine landscape.
• National Institute for Communicable Diseases. Arboviral Disease (disease index and guidance). Johannesburg: NICD; 2025. The source for the South African arbovirus surveillance and clinical context.