Chikungunya — clinical presentation, differential diagnosis, laboratory tests and management

Aetiology. Chikungunya virus is an alphavirus (family Togaviridae), transmitted by the daytime-biting Aedes aegypti and Aedes albopictus mosquitoes. Incubation 3–7 days (range 1–12). The name is Makonde for "that which bends up", describing the stooped posture caused by joint pain. It is endemic and epidemic in India, with recurrent post-monsoon outbreaks, and a major global resurgence occurred in 2024–25.

Acute clinical presentation. Abrupt high fever with severe, symmetrical, incapacitating polyarthralgia and arthritis of the small joints of hands and wrists, ankles and feet; a maculopapular rash on the trunk and limbs in about half; headache, myalgia, conjunctivitis and profound fatigue. In older adults, atypical and severe forms are far more common — encephalitis and encephalopathy, myocarditis, hepatitis, acute kidney injury, Guillain– Barré syndrome, bullous skin lesions, and decompensation of pre-existing diabetes, heart failure and chronic kidney disease. Advanced age is the principal risk factor for severe disease and death: in the 2024–25 La Réunion outbreak, older adults accounted for almost half of all hospitalisations and nearly two-thirds of severe cases with organ failure.

The chronic phase — the defining problem in geriatrics. Persistent or relapsing inflammatory arthralgia and arthritis lasting months to years occurs in up to 40–50% of patients, and is commoner and more severe with increasing age. It closely resembles seronegative rheumatoid arthritis, and it is a major cause of lasting disability, immobility, deconditioning, depression and loss of independence — often more damaging to an older person than the acute illness.

Differential diagnosis. Dengue (thrombocytopenia, haemoconcentration, bleeding and shock; the arthralgia is less severe and does not persist) — co-infection is common, and when in doubt manage as dengue, which is the more dangerous; Zika (milder, prominent rash and conjunctivitis); scrub typhus (eschar, rapid response to doxycycline); leptospirosis (conjunctival suffusion, calf tenderness, jaundice with acute kidney injury); malaria and enteric fever. For the chronic arthritis, the differential becomes elderly-onset rheumatoid arthritis, polymyalgia rheumatica, reactive arthritis and crystal arthropathy.

Laboratory tests — timing determines the test. RT-PCR is the test of choice in the first 5–7 days (the viraemic phase); IgM ELISA (MAC-ELISA) from about day 5 onwards, with IgG appearing later and paired sera showing a four-fold rise. Supportive findings: lymphopenia is characteristic (in contrast to the thrombocytopenia of dengue), with mild thrombocytopenia, raised transaminases and raised CRP. Always test simultaneously for dengue (NS1 antigen and IgM). In the chronic phase, rheumatoid factor and anti-CCP are typically negative, which helps separate it from elderly-onset rheumatoid arthritis.

Management. Entirely supportive — there is no specific antiviral. Rest, adequate fluids and paracetamol for fever and pain. Avoid NSAIDs and aspirin until dengue has been excluded (risk of bleeding and acute kidney injury), and thereafter use them only with great caution in older adults. For inflammatory arthritis persisting beyond three months: a short course of corticosteroids, and in refractory cases hydroxychloroquine or methotrexate under rheumatology supervision. Physiotherapy and graded exercise are essential to prevent contractures, deconditioning and functional decline. Prevention is vector control — source reduction of domestic water containers, mosquito nets, repellents and full-sleeved clothing — remembering that Aedes bites during the day, so night-time bed nets alone are inadequate.

Two chikungunya vaccines are now licensed: IXCHIQ (VLA1553), a live-attenuated vaccine approved in 2023, and VIMKUNYA, a virus-like-particle (non-live) vaccine approved in 2025. Following reports of serious adverse events — including encephalitis and deaths — in vaccinees aged 62 to 89 years, the US FDA suspended the Ixchiq licence in August 2025 and several countries restricted its use above age 60–65; the EMA's PRAC concluded in July 2025 that the overall benefit–risk balance remained favourable and lifted the contraindication in those aged ≥65, with updated product information. Because it is non-live, the VLP vaccine (Vimkunya) is currently the preferred option in older adults, and early post-authorisation data support its safety in over-65s. Neither vaccine is yet available in India, where vector control and early supportive care remain the only strategy.