Describe measles with its clinical features, complications and prevention.

The Virus and Transmission

• A paramyxovirus — enveloped, helical, with single-stranded negative-sense RNA; only one serotype, which is why infection and vaccination both give lifelong immunity and why eradication is theoretically possible
• Surface proteins — H (haemagglutinin) for attachment and F (fusion) protein, which causes cell fusion and the formation of warthin-finkeldey multinucleate giant cells
• One of the most infectious diseases known, spread by respiratory droplets and airborne particles, with a basic reproduction number of 12 to 18 — which is why herd immunity requires about 95% coverage, far higher than for most vaccines
• Infectious from about 4 days before to 4 days after the rash, so transmission occurs before the diagnosis is possible

Clinical Features

Incubation 10 to 14 days → prodrome (3 to 4 days) — high fever with the "three Cs": cough, coryza and conjunctivitis, with photophobia → KOPLIK spots — tiny bluish-white spots on a red base on the buccal mucosa opposite the molars, appearing 1 to 2 days before the rash. They are pathognomonic and allow diagnosis before the rash → rash — an erythematous maculopapular eruption beginning behind the ears and on the face, spreading downward to trunk and limbs, and becoming confluent → The rash fades in the same order, leaving brownish staining and branny desquamation → Transient but profound immunosuppression for weeks to months, with loss of previously acquired immune memory

Complications

• Respiratory — otitis media (the commonest), pneumonia (viral or secondary bacterial, and the commonest cause of death), croup, and reactivation of tuberculosis
• Gastrointestinal — diarrhoea and consequent malnutrition
• Neurological — acute post-infectious encephalomyelitis (about 1 in 1,000, immune-mediated); and subacute sclerosing panencephalitis (SSPE), occurring 5 to 15 years later, particularly after infection under the age of 2, and invariably fatal
• Ocular — keratitis and corneal ulceration leading to blindness, especially where vitamin A deficiency coexists
• In the malnourished and immunosuppressed — giant cell pneumonia without a rash, and greatly increased mortality
• Measles in pregnancy causes abortion and preterm birth, but not congenital malformation (unlike rubella)

Diagnosis, Treatment and Prevention

• The diagnosis is usually clinical, and Koplik spots make it before the rash appears; confirmed by measles-specific IgM from about day 3 of the rash, or RT-PCR on throat swab or urine
• Treatment is supportive — fluids, nutrition, antipyretics, and antibiotics only for proven bacterial complications
• Vitamin A must be given to every child with measles in populations where deficiency occurs — two doses on consecutive days. It reduces mortality and prevents corneal blindness, and is one of the cheapest life-saving interventions in paediatrics
• Vaccine — a live attenuated vaccine, given in India as measles-rubella (MR) at 9 to 12 months with a second dose at 16 to 24 months. The second dose is not a booster but a chance to reach those in whom the first failed
• Post-exposure prophylaxis — vaccine within 72 hours, or immunoglobulin within 6 days for susceptible high-risk contacts

Applied Aspects

• Give vitamin A to every child with measles; this single measure measurably reduces death and blindness and is frequently omitted
• 95% coverage is needed for herd immunity, which is higher than for any other routine vaccine and explains why measles is the first disease to return when coverage falls
• SSPE is entirely preventable by vaccination and still occurs in India; infection before the age of 2 carries the highest risk, so timely vaccination matters as much as eventual vaccination
• Isolate suspected cases and notify; measles is airborne and highly transmissible in waiting rooms and wards, and hospital-acquired measles is well documented
• Look in the mouth in any febrile rash with cough, coryza and conjunctivitis — Koplik spots settle the diagnosis at no cost
• Measles is a sensitive indicator of programme failure; an outbreak signals a gap in coverage long before other vaccine-preventable diseases reappear