Measles

Overview

Measles (rubeola) is an acute, very contagious viral illness, mainly of young children. It is still a major cause of child death in countries with low vaccine coverage, including Pakistan, where outbreaks occur regularly.

Deaths come from pneumonia, diarrhoea and malnutrition, made worse by vitamin A deficiency. Measles also suppresses immunity for weeks to months after recovery.

Aetiology and transmission

• Agent: measles virus, an RNA paramyxovirus (genus Morbillivirus). There is only one serotype, so one infection or full vaccination gives lifelong immunity.
• Reservoir: humans only; no carriers.
• Spread: respiratory droplets and droplet nuclei (airborne); the virus can hang in room air.
• Infectious period: roughly 4 days before to 4 days after the rash appears; most infectious in the prodrome.
• Incubation: about 10 days to the fever and 14 days to the rash.
• Age: in poor settings, mostly 6 months to 3 years; babies under 6 months are usually protected by maternal antibody.

Pathophysiology

• The virus enters through the respiratory tract (and conjunctiva), multiplies in lymphoid tissue and spreads in the blood to skin, lungs, gut and other organs.
• It causes multinucleated giant cells (Warthin–Finkeldey cells in lymphoid tissue).
• The rash is an immune reaction: T cells attack infected cells in small skin vessels. Patients with poor cell-mediated immunity may have no rash but severe pneumonia.
• Measles causes temporary immunosuppression: the tuberculin (Mantoux) test can turn negative, and latent TB may reactivate.

Clinical features

1. Prodromal (pre-eruptive) stage: 2–4 days

• High fever.
• The "3 Cs": cough, coryza, conjunctivitis (red, watery eyes, photophobia).
• Koplik spots: small, bluish-white spots on a red base, like grains of salt, on the buccal mucosa opposite the lower first and second molars. They appear 1–2 days before the rash and fade as it spreads.

2. Eruptive stage

• Dusky-red maculopapular rash begins behind the ears and along the hairline/face.
• Spreads downwards to the trunk and limbs over 2–3 days; patches often merge (confluent).
• Fever is highest when the rash appears, then falls.
• The rash fades in the same order, leaving brownish staining and fine peeling.

3. Post-measles stage

• Weight loss, weakness, diarrhoea, reactivation of TB, mouth infections such as cancrum oris (noma) in malnourished children.

Complications

Subacute sclerosing panencephalitis (SSPE)

• A rare, progressive, fatal disease from persistent defective measles virus in the brain.
• Appears 7–10 years after measles that occurred in infancy.
• Features: personality and school decline, myoclonic jerks, dementia, then coma and death.
• Diagnosis: very high measles antibody titres in CSF and serum; characteristic periodic complexes on EEG.

Investigations

• Diagnosis is mainly clinical: prodrome + Koplik spots + typical rash.
• A positive measles IgM antibody (serum or saliva) confirms it.
• RT-PCR on throat or nasopharyngeal swab, or urine.
• Leucopenia is common.
• CXR if pneumonia suspected.

Differential diagnosis

Management

There is no specific antiviral. Care is supportive:

• Isolate the child (airborne precautions) until about 4 days after rash onset.
• Fever control, fluids, continue feeding (breastfeeding).
• Vitamin A to every child with measles.
• Antibiotics only for secondary bacterial infection (pneumonia, otitis media).
• Treat complications; nutritional rehabilitation.

Vitamin A doses (given on diagnosis and repeated the next day)

• If there are eye signs of vitamin A deficiency (for example Bitot spots), give a third dose 4–6 weeks later.

Prevention

Active immunisation

• Live attenuated vaccine, given subcutaneously (also works IM).
• Pakistan EPI: measles-rubella (MR) vaccine at 9 months and 15 months.
• Not given earlier than 9 months routinely because maternal antibody blocks the response; in an outbreak it can be given from 6 months (that dose is then not counted).
• Reconstituted vaccine is heat- and light-sensitive: keep at 2–8 °C in the dark and discard after 4 hours. Reusing an old vial can cause toxic shock syndrome.
• Contraindicated in pregnancy and in severe immunosuppression. After MR vaccine, women should avoid pregnancy for about 1 month.
• HIV-positive children who are not severely immunosuppressed should be vaccinated.

Post-exposure prophylaxis

• Measles vaccine within 72 hours of exposure can prevent or modify disease in susceptible people over 6 months old.
• Human normal immunoglobulin within 6 days of exposure for those who cannot have a live vaccine: infants under 6 months, pregnant women, the immunocompromised.

Epidemiology terms often asked

• Secondary attack rate = new cases among susceptible contacts within one incubation period ÷ number of susceptible contacts.

• Measles vaccination is specific protection, a form of primary prevention.

Quick revision

• Paramyxovirus, one serotype, droplet/airborne, humans only.
• Incubation: about 10 days to fever, 14 days to rash.
• 3 Cs + fever → Koplik spots → rash from head downwards.
• Infectious 4 days before to 4 days after rash.
• Pneumonia kills most; diarrhoea and otitis media are also common.
• SSPE: years later, myoclonus, high CSF measles antibody.
• Vitamin A on diagnosis and next day (50,000 / 100,000 / 200,000 IU by age).
• MR vaccine at 9 and 15 months; post-exposure vaccine within 72 h.

Written by The House Job from standard references (Kumar and Clark's Clinical Medicine; Park's Textbook of Preventive and Social Medicine; Levinson's Review of Medical Microbiology and Immunology).

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