Measles has been with us for more than 1,400 years. In the 10th century, the Persian physician Rhazes wrote a treatise on it distinguishing it from smallpox. But it would take another millennium to identify the virus that causes measles — from the paramyxovirus family — and develop a vaccine against it.

Until 1963, when the first vaccines were introduced, measles was an inevitable part of growing up, much as chickenpox is today. Since the effects and complications of measles are less severe during childhood than during adulthood, measles parties were a regular social fixture.

The highly contagious virus is spread through droplets issued from coughs and sneezes, like the common cold. The virus normally grows in the cells that line the back of the throat and in the cells that line the lungs.

It has an incubation period of about ten days (up to three weeks in the immunosuppressed), after which a fever, cough, runny nose and conjunctivitis develop. The fever can peak at 40C (104F), and last between one and seven days. The characteristic red blotchy rash arrives about four days after the fever — starting on the head and working its way downwards to envelop the whole body. It turns brown before disappearing.

Bluish spots inside the mouth, called Koplik spots, can be used to confirm diagnosis, although the spots can be short-lived. Diagnosis is usually made from the combination of fever and other symptoms.

An infected person can remain contagious for up to five days after the fever first appears. Provided there are no complications, the disease takes about a fortnight to run its unpleasant course and the child is left with lifelong immunity.

Relatively mild complications include earache, vomiting, diarrhoea and abdominal pain. But other complications can be severe, including blindness, convulsions, pneumonia, brain damage and death. The most vulnerable patient groups for complications are under-5s, adults over 20 and immunosuppressed patients.

Among infected young children, the most common cause of death is pneumonia (particularly in developing countries), and among adults it is encephalitis (brain inflammation). The Health Protection Agency (HPA) states that fewer than 1 in 1,000 infected individuals develop encephalitis but, of these, a quarter are left brain-damaged. There is also an extremely small risk — less than 1 in 100,000 — of acquiring a slow, progressive brain infection that manifests itself years after infection.

Subacute sclerosing pan-encephalomyelitis (SSPE) first causes intellectual impairment, then seizures and then death. The HPA notes that, prior to 1988, half of all the children who died from measles were previously healthy.

If the measles virus is circulating, and unvaccinated children are exposed, they are highly likely to catch it. There is no cure, although symptoms can be treated. Antibiotics can be used to treat ear infections and bacterial infections, and the patient rehydrated. The fever can be controlled with drugs. Human normal immunoglobin (HNIG) can also be given to reduce the severity of an attack.

This mix — high transmissibility, lack of a cure, plus the chance of complications — means health professionals advocate measles prevention as by far the best strategy. The World Health Organisation would like to see the disease, which kills around half a million people a year, mostly in developing countries, eradicated by 2010.

Measles has been all but wiped out in Britain thanks to a nationwide immunisation programme; the MMR (measles, mumps and rubella) vaccine was introduced in 1988 and there have been no deaths from acute measles since 1992. The several deaths since 1992 attributable to measles have been due to infections stemming from the 1980s, which have led to such conditions as SSPE.

Measles remains a notifiable disease, which means that doctors who diagnose a case are legally obliged to report it to the HPA, which can predict possible outbreaks and control them.