The virus

Measles is an RNA virus belonging to the family Paramyxoviridae.

Epidemiology

Route of spread

Measles is highly infectious with a high secondary infection rate in contacts, especially household contacts. The infection is spread by the respiratory droplet route.

Prevalence

Measles has a worldwide prevalence with most infections occurring in childhood. In the Western world infection below the age of one year is unusual, due to protection offered by maternal antibody. In the developing world, however, due to poor acquisition of maternal antibody, measles under one year is common and has a high mortality rate because of secondary bacterial infection and poor nourishment. Measles was endemic in the UK with epidemics occurring every 2–3 years prior to the introduction of the childhood measles, mumps and rubella (MMR) vaccination programme in the mid 1980s. However, outbreak clusters have occurred recently because of the fall in the uptake of measles vaccination. Humans are the only host and the World Health Organization estimates that worldwide there are over a million childhood deaths due to measles each year, and has declared measles as one of the infections to be eradicated from the world.

Incubation period

10–15 days, an average of two weeks.

Infectious period

Prodromal period (2–3 days before the rash appears) to about 4 days after the rash appears.

At-risk groups

All susceptible individuals, but especially those who are immunocompromised or pregnant.