Small but deadly threat

To most of us, smallpox is a disease of the past. The virus that helped the Spanish conquistadores destroy the Incas, that swept through native American populations and contributed to the downfall of the Roman Empire, was in 1977 finally extinguished, thanks to vigorous programmes of ring-vaccination.

The last naturally occurring case was a hospital cook in Somalia. Fifty-seven-thousand people around him were vaccinated and the life cycle of the virus was halted.

Variola, the smallpox virus, is a uniquely human disease, only able to replicate inside a person's body. The fact that it is airborne, says Richard Preston in his alarming new book, The Demon in the Freezer, makes it the perfect bioterrorist weapon, a fact exploited some 240 years ago by Sir Jeffrey Amherst, the head of the British forces holed up at Fort Detroit

against the might of the Indian forces.

In a letter to one of his field officers, Amherst gave instructions for blankets from the smallpox hospital to be given to two unsuspecting Indian chiefs. Smallpox proceeded to burn through the human population of the Ohio River.

Since 9/11, and the subsequent anthrax attacks in the US, bioterrorism has reemerged as a major international threat and - with impressive insider access - Preston explains why, of all diseases, it is smallpox that is most to be feared.

Combining history of the disease with reconstructions of outbreaks, clinical detail with in-depth descriptions of research currently underway, he issues a sombre

warning. Smallpox, he believes, is likely to be in the possession of both Iraq and North Korea and could be bought by terrorist groups.

The source of this smallpox is likely to have been the Soviet Union, which back in the late 1980s was developing and stockpiling weaponsgrade smallpox, Preston claims. Quoting former Soviet scientists, and current US researchers, he explains how, by the time the USSR fell in 1991, its bio-weapons plan was "quite advanced".

The smallpox was designed to be delivered from biowarheads, which would float to earth on parachutes, bursting apart as they neared the ground to throw out fans of carbon-dioxide-pressurised bomblets, each of which would let out a deadly mist of variola.

No one knows for sure the current whereabouts of the 200 tons of weapons-grade smallpox that the Soviets are known to have possessed in

1989. Kept refrigerated, smallpox can survive for many decades.

Preston - who made his name with the bestselling The Hot Zone - has considerable relish for the gory side of what he describes as "dark biology", and his prose sparks to life when dealing with the human effects of disease.