The return of smallpox - one of the most lethal diseases in history - is a terrifying possibility, according to the scientist who ran the World Health Organisation's campaign to eradicate the virus in the 1970s.
Donald Henderson, a senior science adviser to the US government, said past assurances from certain countries claiming to have destroyed their smallpox stocks could no longer be believed. At least 30 million people are thought to have died from the disease in the 20th century.
WHO scientists declared smallpox eradicated in 1980 after a prolonged global vaccination campaign, but there are fears that the virus may still be in the hands of a rogue state or a terrorist group.
Dr Henderson said smallpox might have been retained by some governments despite their guarantees that all remaining stocks were either destroyed or sent to one of two official repositories controlled by the WHO. "The question is, were we sure we had smallpox left in only two laboratories at the end of the eradication programme? There was no way we could guarantee that,'' Dr Henderson said yesterday.
In 1989, a Soviet defector revealed that his government had an extensive and illegal biological weapons programme involving the production of up to 20 tons of smallpox. Dr Henderson yesterday told a smallpox conference in Geneva that other countries, such as Iraq, Syria and Iran, might have retained stocks of smallpox from a naturally occurring outbreak in 1972.
"Our feeling was, we were more complacent, if that's the proper word, earlier on because we did not know of the Russian activities,'' Dr Henderson told The Independent.
Asked whether he believed that all governments involved in the eradication campaign destroyed their samples, Dr Henderson said: "No, I don't. I have no way of knowing whether they did or they didn't.'' He said that the WHO took governments on their word because at that time there was very little talk about the possibility of using smallpox as a biological weapon.
"There was a feeling on the part of many people that there was some sort of moral barrier that nobody would ever transgress. And there were some who said it is just too difficult. Well, it isn't that difficult. You can produce it.
"We just have to say the difference now is simply the concern that there are groups who would like to use biological weapons,'' he said.
Dr Henderson warned that the return of smallpox would be extremely serious.
"The return of the most deadly and feared pestilent of all time to a world now more susceptible than at any time in history could result in a catastrophe of unimaginable proportions,'' he said.
Smallpox is caused by a virus called Variola, which kills about one third of those it infects, leaving survivors badly scarred. Initial symptoms are high fever and general sickness, followed by pustules, which form painful blisters.
There are no effective treatments but vaccination is almost 100 per cent effective. A carrier can infect between three and 10 others, making the virus an effective terrorist weapon. The disease can be caught by breathing in water droplets or absorbing the virus through membranes around the eyes.Reuse content