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Measles

Epidemiology of Infectious Diseases: Measles

Causal agent
Measles virus; an acute and highly infectious viral illness of the paramyxovirus family. 

Common clinical features

  • Prodromal illness with high fever, coryza,  respiratory infection, conjunctivitis and Koplik's spots in the mouth.
  • Characteristic rash (raised red blotches) appears on the 3-7th day,  initially on the face and then becoming generalized lasting 4-7 days.
  • An estimated 20% of measles cases experience one or more complications including otitis media, pneumonia, corneal scarring, croup, diarrhoea and encephalitis.
  • Complications are more common in children under 5 years and in adults over 20 years.
  • Case fatality rates range from 3-5% increasing to 10-30% among the immunocomprised,  malnourished and children suffering from clinical or subclinical vitamin A deficiency.
  • Measles infection among pregnant women can lead to a higher risk of spontaneous abortion, premature labour and low birth weight. 

Epidemiology

  • Endemic worldwide - measles is the leading cause of death among young children. In 2004 an estimated 454,000 people died from measles (most of them children in developing countries).
  • Measles is the leading cause of blindness among children in Africa.
  • Until the introduction of measles vaccine in the UK in 1968, annual notifications varied between 160,000 and 800,000 with peaks every two years1.
  • However, due to low coverage rates notifications of between 50,000 and 100,000 were still reported in the UK. Since the introduction of the MMR vaccine in 1998 and increases in coverage rates were achieved (over 90%) measles transmission has been significantly reduced1.

Reservoir
Humans - no known animal reservoir.

Mode of transmission
Person to person via droplet infection or direct contact with nose and throat secretions of infected persons. 

Almost all non-immune children exposed to the measles virus will become infected.

Incubation period
From exposure to prodrome average 10-12 days. From exposure to rash onset average 14 days (range of 7-18 days).

Period of Communicability
From 1 day before the beginning of the prodromal period until 4 days after the appearance of rash.

Prevention and control

  • Routine MMR vaccination, 2 doses at 12-15 months and at 4 years of age. There is no upper age limit and where required, two doses can be given separated by at least a one month interval.   

References

  1. Salisbury DM, Begg NT.  Immunisation against infectious disease (The green Book). London: HMSO, 1996. Available at http://www.dh.gov.uk/assetRoot/04/07/29/84/04072984.pdf

Further Resources

www.measlesinitiative.org

© CM Kirwan 2006