When eradication was achieved, it was a tremendous boost to public health in general

Professor Paul Fine, London School of Hygiene and Tropical Medicine

But a new virus - HIV - has become a massive problem in parts of the world, while other life-threatening illnesses, such as diphtheria, tetanus and measles have resisted attempts to extinguish them.

Smallpox is characterised by headache, vomiting and fever followed by the eruption of a widespread rash.

The eruption follows a set pattern, commencing on the head and face and when the final stage is passed disfiguring scars are left on the skin.

Discovery

The road to eradication of smallpox started more than 200 years ago when scientist Edward Jenner made a discovery which led to the development of a vaccine.

He noticed that milkmaids who had developed cowpox from contact with cow udders were protected from the human form of the disease, and the cowpox virus became the basis of his vaccine.

The vaccination became compulsory in Britain during the 19th century, but by 1971 it was no longer necessary as the virus had been stamped out in the West.

Efforts continued to destroy smallpox in parts of the world where it remained - primarily Africa and Asia - throughout the 1970s.

A policy of isolating cases and vaccinating people who had come in contact with the patient proved very successful and eventually led to its eradication in these regions as well.

The last recorded case of human to human transmission came in October 1977 when a cook called Ali Maow Maalin, living in a Somali village, contracted the illness.

The final death, however, occurred in the UK the following year when an accident in a Birmingham laboratory killed a medical photographer.

Smallpox is 'easily recognisable'

Debate has continued about the storing of stocks of the smallpox vaccine, which were supposed to have been destroyed but continue to be held by the US and Russian governments.

Eradication was hailed as a success for the World Health Organisation, but its attempts to eliminate other, more complex, viruses have not been so successful.

Paul Fine, professor of communicable disease and epidemiology at the London School of Hygiene and Tropical Medicine, said: "When eradication was achieved, it was a tremendous boost to public health in general. It was tremendously important."

But he added: "Smallpox was a relatively easy target. It is easy to recognise, it is easy to drum up public and political support to get rid of it, because it is a killer, there is no animal reservoir and it is not as transmittable as something like measles."

The challenge for the medical world now is to successfully tackle the remaining viruses claiming millions of lives each year.