Write a short note on chikungunya.

Aetiology

Chikungunya is caused by the chikungunya virus (CHIKV), a single-stranded RNA alphavirus of the Togaviridae family, transmitted by the daytime-biting *Aedes aegypti* and *Aedes albopictus* mosquitoes — the same vectors as dengue, which is why the two frequently co-circulate and co-infect.

The name derives from a Makonde word meaning "that which bends up", describing the stooped posture of patients crippled by joint pain. India has experienced large epidemics since the major resurgence of 2005–06, and the disease is now endemic with recurrent outbreaks, particularly post-monsoon.

Incubation: 2–7 days (range 1–12).

Pathogenesis

The virus replicates in skin fibroblasts and disseminates to muscle, joints, liver and lymphoid tissue, causing a vigorous innate immune and interferon response. Persistent viral antigen and RNA within joint tissue and macrophages, together with an ongoing inflammatory response, is thought to underlie the prolonged arthritis that characterises this infection and distinguishes it from dengue.

Clinical Features

Acute phase (first 1–2 weeks):

• Abrupt high fever — typically sudden in onset, lasting 3–7 days.
• SEVERE, SYMMETRICAL, INCAPACITATING POLYARTHRALGIA — the hallmark. It affects small joints of the hands, wrists, ankles and feet predominantly, is often bilateral, and is frequently so severe that the patient cannot walk, hold objects or stand upright — hence the "bent-up" posture. Frank arthritis with swelling occurs in a substantial proportion.
• Rash — maculopapular, on the trunk and limbs, sometimes with intense pruritus; hyperpigmentation, particularly of the nose ("chik sign") and centrofacial region, is characteristic and may persist.
• Headache, myalgia, backache, fatigue, conjunctivitis, nausea.
• Haemorrhagic manifestations are uncommon and mild — an important contrast with dengue.

Subacute and chronic phase:

• Persistent or relapsing polyarthralgia and arthritis lasting months to YEARS in up to 30–50% — the most important long-term consequence. It is symmetrical, involves small joints, and may closely mimic rheumatoid arthritis, but is seronegative and non-erosive. Morning stiffness, tenosynovitis and Raynaud's phenomenon may occur.
• Fatigue and depression are common.

Severe and atypical disease (in neonates, the elderly and those with comorbidity): encephalitis, myelitis, Guillain–Barré syndrome, myocarditis, hepatitis, acute kidney injury, and bullous skin lesions in infants. Vertical transmission around the time of delivery can cause severe neonatal disease.

CHIKUNGUNYA versus DENGUE — A KEY DIFFERENTIATION

Both may co-infect the same patient, and when in doubt, manage as dengue, since dengue carries the risk of shock and requires the more careful fluid monitoring.

Investigations

• RT-PCR — the test of choice in the first 5–7 days, when viraemia is present.
• IgM ELISA — positive from about day 5, persisting for months.
• IgG — rising titres in paired sera; indicates past infection.
• Test for dengue simultaneously — NS1 antigen and IgM — because co-infection and clinical overlap are common.
• Supporting: lymphopenia (characteristic), mild thrombocytopenia, raised ESR and CRP, mildly raised transaminases. Rheumatoid factor and anti-CCP are negative, which helps distinguish chronic chikungunya arthritis from rheumatoid arthritis.

Management

There is no specific antiviral treatment; management is symptomatic.

Acute phase:

• Rest, adequate oral fluids and hydration.
• Paracetamol for fever and pain.
• AVOID aspirin and NSAIDs until dengue has been reliably excluded — because if the illness is dengue, they increase bleeding risk. Once dengue is excluded, NSAIDs are the mainstay for the joint pain and are considerably more effective than paracetamol alone.
• Cold compresses and gentle mobilisation for joint pain.

Subacute and chronic arthritis:

• NSAIDs as first-line.
• Short courses of corticosteroids for severe persistent inflammatory arthritis unresponsive to NSAIDs.
• Hydroxychloroquine, sulfasalazine or methotrexate for prolonged, disabling, rheumatoid-like disease, managed with rheumatology input.
• Physiotherapy and graded exercise — important and often neglected; maintains joint range and function.
• Patient education about the expected duration, since the persistence of symptoms causes considerable anxiety and repeated investigation.

Prevention

Identical to dengue, and the two programmes are the same: source reduction of *Aedes* breeding sites (domestic water containers, coolers, tyres, discarded receptacles), weekly "dry day" practices, larvicides, personal protection with repellents and full-sleeved clothing (noting the daytime biting habit, so bed nets alone are insufficient), and community participation. Isolate viraemic patients under bed nets during the first week to prevent onward transmission. There is no widely deployed vaccine.