What is Measles?

Measles used to be common in childhood but now affects just a few thousand a year, thanks to widespread vaccination. But, the illness is still a threat worldwide - killing a million children each year, mostly in developing countries.

How do you catch measles?

Measles is caused by a virus that is spread by droplets. The virus is passed on through direct contact with someone who's infected, for example by touching or kissing them, or through breathing in contaminated air. It's fairly easy to catch if you haven't been vaccinated and come into contact with someone who has the infection, which is why epidemics often occur among schoolchildren.

The infectious period is from four days before the rash to four days after it's appeared. Unfortunately it's most nfective before the rash appears so people tend to spread the virus before they realise they have it. Although people of any age can get measles, it's most common among those aged between one and four.

Who is at increased risk from measles?

• young babies under one year
• People whose immune system is suppressed, for example by cancer or HIV
• malnourished people
• children with vitamin A deficiency
• pregnant women - the infection may cause miscarriage or premature delivery

Who's affected by measles?

All children who've not been vaccinated are at risk from measles, and those who have problems with their immune system (particularly with T lymphocytes) may suffer from a more severe illness.

Children in developing countries are more at risk - limited vaccination, malnutrition and vitamin A deficiency often impair a child's immunity and their ability to fight the infection. However, in the developed world, apart from some worries about the measles vaccine and possible links to autism or the inflammatory bowel disease, Crohn's disease, most parents hardly give measles a second thought.

What are the symptoms?

Symptoms take about ten to 14 days to develop after exposure to the virus (the incubation period). Early symptoms are like a cold, with runny nose, cough, conjunctivitis and fever. A couple of days later tiny white spots surrounded by red (Koplik spots) may develop on the inside mucosa of the cheeks. These are diagnostic of measles but difficult to see.

The measles rash appears a day or two later, starting behind the ears or on the face and spreading down across the body. It's a fine red rash which becomes blotchy and confluent, fades after three to four days and may peel off after a week or so. Abdominal symptoms may include nausea and vomiting, abdominal pain and diarrhoea. Symptoms usually last about 14 days in all and it's recommended that children stay off school for five days after the start of the rash.

The infection isn't usually serious but there's a risk of potentially fatal complications, even for healthy children. These include otitis media, pneumonia, hepatitis, conjunctivitis and encephalitis (inflammation of the brain, this occurs in about one in 5,000 cases). Although complications involving the nervous system occur in less than 1 in 1,000 cases, the long-term effects can be devastating.

Encephalitis or inflammation of the brain may develop a few days after the rash has appeared, and a quarter of those who get this complication will be left with brain damage and a devastating but extremely rare illness called subacute sclerosing panencephalitis (SSPE). This progressive illness may develop many years after the first bout of measles and is eventually fatal. Fortunately it's very rare, occuring in fewer than one in 100,000 cases.

How is it diagnosed and treated?

See your doctor to confirm the diagnosis. Children may be treated at home with pain and fever-reducing syrups such as paracetamol and they should be encouraged to drink fluids.

The child is infectious from one day before the onset of symptoms until around five days after the start of the rash, so let friends, family and other potential contacts know. Hospital treatment, with antiviral drugs, may be needed in more serious cases. In developing countries vitamin A may also be given to help the immune system.

Vaccination against measles

Children in the UK are offered vaccination against measles as part of the MMR vaccine given at between 12-15 months of age (with a booster dose before starting school).

There's been concern about possible risks from vaccination, especially with the combined MMR vaccine, after several researchers (including one at the Royal Free Medical School in London) suggested links with either autism or Crohn's disease.

However, the debate is raging on see bbc.co.uk/news. However, the overwhelming body of evidence doesn't support these worries and most experts are emphatic that the MMR vaccine is safe and effective, preventing illnesses whose real potential to cause damage most of us have lost sight of. These infections cannot be beaten in any other way. The Department of Health has a summary.

Top tips

Don't lose sight of the fact that measles can, and does, kill and do long-term harm. Vaccination prevents this risk. Measles is a notifiable disease - if you think your child may have it, see your doctor at once. They can confirm the diagnosis with a simple saliva test and must then let the local health authority know. Some children may possibly be at risk from vaccination - for example, a child who's had febrile fits or existing nervous system problems. Talk to your doctor. A vaccine for each infection may be given instead of the MMR vaccine in certain cases, for example, if your child has an allergy. But, it's now extremely difficult to get hold of the separate vaccines. Ask your doctor for more advice.

Further help

Although rare, complications can be very dangerous. Encephalitis, for example, typically develops after about eight days, with headaches, lethargy and irritability, progressing to convulsions, coma and death in 15 per cent and long-term health problems in nearly half of survivors. If your child shows any worrying symptoms during measles get urgent medical advice.

See the parents guide giving answers to common immunisation questions.