Deadly disease eradicated in its natural form

SMALLPOX was eradicated in its natural form following a global vaccination programme.

The last case of endemic smallpox was in Somalia in 1977 and the last case in the world was a laboratory-acquired infection in 1978.

However, there are fears that smallpox still exists in laboratory conditions and could be used during a terrorist attack. Smallpox is caused by the variola virus and there are two forms variola major, which is the more deadly form, and

variola minor, which is less severe. Smallpox typically kills a third of those infected and is spread between people through the air or by skin contact.

It is difficult to treat because it is a virus and the best form of defence is vaccination, which can be effective even if given within the first few days after exposure to the virus. The incubation period is usually between 12 and 14 days and the first symptoms are typically a headache, backache and high fever followed by a rash of fluid filled blisters.

Britain has chosen to stockpile a vaccine for a strain of smallpox known as the Lister strain. And last month, chief medical officer Liam Donaldson revealed Britain had enough smallpox vaccine stocks for 30 million people. However, the US is stocking up on another type of vaccine which it believes would be more effective against the kind of type that might be used by terrorists.

Last month, a study published in Science magazine suggested that vaccinating people in close contact with smallpox victims could be just as effective as giving the jab to the entire population. It suggested one way to increase the level of existing immunity in the population might be to vaccinate hospital workers and volunteers as these were most likely to encounter the virus.

Elizabeth Halloran, who headed the research, said: "The last thing you want is thousands of people running out to get vaccinated after smallpox has been introduced. The idea is that people should just stay calm and stay at home."