Measles

Measles in short                       

•  a very contagious viral disease
• symptoms include high fever, rash, cough, a runny nose and red, watery eyes
• about 20% of patients experience complications such as ear infections, diarrhoea, pneumonia or encephalitis
• unimmunized young children under 5 years of age are at highest risk for complications
• a safe and effective vaccine is available
• immunity (after vaccination or infection) lasts a lifetime
• most deaths occur in poor countries, especially in Africa
• worldwide immunization efforts led to a 74% reduction in measles deaths (89% reduction in Africa) between 2000 and 2007

Measles in detail

Pathogenic agent       
The measles virus belongs to the genus Morbillivirus within the family of Paramyxoviruses. It is a single-stranded RNA virus (ssRNA). The nonsegmented helical RNA is associated with nucleocapsid protein N in form of a nucleocapsid. The lipid-bilayer envelope carries two transmembrane viral proteins named haemagglutinin (HA) and the fusion protein (F). The size of the virions varies, with diameters of most particles ranging from 120 to 350 nm.

The virus is easily destroyed by light, high temperatures, UV radiation or disinfectants. Outside its host it can survive for up to 2 hours. Infected humans are the only reservoir of the virus.

Transmission/ pathogenesis
Measles is one of the most contagious diseases known. The virus resides within the nose and throat of infected persons and is easily spread by coughing, sneezing or by close contact. The contagion index reaches nearly 100%, meaning that nearly every unimmunized person coming in close contact with a patient will also become infected with measles.

The virus enters the body through the upper respiratory tract or the conjunctiva. It then spreads to the lymph nodes, where the first viraemia starts. During the second viraemia the virus spreads to the skin, kidney and bladder.

Symptoms
After an incubation period of about 10 to 12 days during which the infected person is symptom-free, first signs of the infection show. These may include fever, malaise, sneezing, rhinitis, cough and conjunctivitis. White Koplik’s spots appear on the oral mucosa. After a couple of days, the typical rash appears, starting behind the ears and on the forehead and eventually spreading over the whole body to finally reach the hands and feet of the patient. The rash typically last for 5 to 6 days and then fades. Measles patient are contagious from approximately 4 days prior to 4 days after the onset of the rash.

Complications
Measles is commonly a mild or moderately severe illness. However, approximately 20% of infected people experience one or more complications, mainly children under 5 years of age or adults above 20 years of age. Undernourished or vitamin A-deficient children have the highest risk of severe complications. Measles deaths are not caused by the virus itself but by the complications.

Bacterial infections
The transient suppression of immunity accompanying measles infection enables secondary bacterial infections - the most common complications of measles – to take hold. Ear infections are reported in 5–15% of measles cases, and 1 out of 20 children with measles gets pneumonia, the most common cause of death associated with measles.

Diarrhoea
Diarrhoea can lead to dehydration and thus severely threaten the life of infected persons, especially young and poorly nourished children.

Acute measles encephalitis
Around 1 child in 1000 develops acute measles encephalitis, an inflammation of the brain that can lead to convulsions and can have severe consequences, such as deafness or mental retardation. The mortality rate of measles encephalitis is around 15%.

Subacute sclerosing panencephalitis (SSP)
This fatal complication occurs in 1–10 patients in 100,000 and usually starts 6 to 8 years after the initial measles infection. First signs are intellectual deterioration or psychological disturbances, and other neurological symptoms, e.g. convulsions or aphasia, follow. The disease progresses slowly with a highly variable course. Some 75% of patients go blind during the course of infection. The illness lasts 1 to 3 years and inevitably leads to death.

Measles in pregnancy
An infection during pregnancy often results in spontaneous abortion or premature birth. Some surviving infants develop only mild disease, while others show severe symptoms and complications, often pneumonia.

Treatment
Measles is a self-limiting disease, and there is no treatment for the virus infection itself. However, complications can be avoided, for example through nutritional support. Antibiotic treatment might be indicated in cases of bacterial superinfection (pneumonia or otitis media). According to World Health Organization (WHO) recommendations, children in developing countries should receive vitamin A supplements to prevent eye damage and blindness.

Vaccination
A safe, effective and inexpensive vaccine is available. The measles vaccine is a live, attenuated vaccine often combined with the rubella and/or mumps vaccine (MR or MMR). Immunization coverage rates vary considerably by region. Countries with high rates have very low measles incidence, and cases that do occur are often imported. In general, illness is rare in most industrialized countries. However, suboptimal vaccination rates - even in developed countries - still support the circulation of the virus.

Incidence and mortality
Between 2000 and 2007, the number of measles-related deaths worldwide fell by 74%, from an estimated 750,000 to 197,000, according to the latest WHO data. In Africa, the death rate fell by 89%, and the Eastern Mediterranean region (including Afghanistan, Pakistan, Somalia and Sudan) has cut measles deaths by a remarkable 90%, thereby achieving "the United Nations goal to reduce measles death by 90% by 2010 3 years early," the WHO reports.

More information
- World Health Organization (WHO): www.who.int/topics/measles/en/
- Centers for Disease Control and Prevention (CDC): www.cdc.gov/ncidod/diseases/submenus/sub_measles.htm
- The Measles Initiative: www.measlesinitiative.org
- The Robert Koch Institute (in German only): www.rki.de/cln_091/nn_494538/DE/Content/Infekt/EpidBull/Merkblaetter/Ratgeber__Mbl__Masern.html

Literature
- WHO fact sheet on measles: www.who.int/topics/measles/en/
- The Measles Initiative, measles statistics 2007 - Global measles deaths drop by 74%: www.who.int/mediacentre/news/releases/2008/pr47/en/index.html
- CDC on measles: www.cdc.gov/ncidod/Diseases/submenus/sub_measles.htm