Measles

Overview

•Caused by a paramyxovirus; spread via respiratory droplets/aerosol

•Incubation 10-14 days; infectious from 4 days before rash until 4 days after

•R0 of 12-18 - one of the most infectious pathogens known

Risk Factors

Unvaccinated/incompletely vaccinated - most important

Age under 1 year - too young for vaccine

Immunocompromise - risk of severe disease

Vitamin A deficiency - increased mortality

Travel to endemic areas

Pregnancy - premature labour, miscarriage, pneumonia

Presentation

•Prodrome (days 1-4): high fever + the 3 Cs - Cough, Coryza, Conjunctivitis

•Koplik spots - pathognomonic; small white/bluish-white spots on red base on buccal mucosa (opposite lower molars); appear 1-2 days before rash, fade as rash develops

•Maculopapular rash - appears day 3-4; starts behind ears/face then spreads head-to-toe over 3 days

•Fever peaks as rash appears then subsides; photophobia common

💡

Koplik spots are the only pathognomonic feature of measles - they appear before the rash and disappear as it develops. White buccal spots + fever + 3 Cs = measles until proven otherwise.

Investigations

•Notifiable disease - notify local Health Protection Team (HPT) on clinical suspicion; do not wait for lab confirmation

🥇 First-line

•oral fluid (saliva) measles IgM and PCR - preferred UK method

•Serum measles IgM - detectable from rash onset; may be negative in first 72 hours

•Throat swab/urine PCR - useful in immunocompromised (may not mount antibody response)

•FBC - lymphopenia characteristic; CXR if pneumonia suspected

Management

•Notify HPT immediately on clinical suspicion

•Isolation - stay home for 4 days from rash onset

•Supportive care - fluids, paracetamol or ibuprofen for fever

•Vitamin A supplementation - consider in children under 2 years; reduces severity and mortality

•Hospital admission if: shortness of breath (pneumonia), persistent/worsening fever, convulsions, confusion, or signs of encephalitis

⚠️

If a child with suspected measles needs to attend hospital, telephone ahead so isolation can be arranged before arrival - avoid exposing immunocompromised patients and unvaccinated infants in waiting areas.

Prevention

•MMRV vaccine (from July 2024) - two doses required

•First dose: 12-13 months

•Second dose: 3 years 4 months (pre-school booster); minimum 4 weeks apart if given earlier

•Two doses provide ~97% protection; herd immunity requires ~95% population coverage

Complications

•Higher risk in: under 5s, over 20s, immunocompromised, malnourished, pregnant women

•Pneumonia - most common cause of measles-related death

•Encephalitis - acute; presents during or shortly after rash

•SSPE (subacute sclerosing panencephalitis) - rare, universally fatal late complication; presents 7-10 years after infection with progressive cognitive decline, myoclonic jerks, and vegetative state; higher risk if measles before age 2

•Immune amnesia - measles destroys memory B and T cells, leaving child susceptible to other infections for months to years

🚨

SSPE is universally fatal with no cure - it is a key reason why MMR is offered at 1 year, as natural measles in infancy carries the highest SSPE risk.