Mankind has always been in battle with disease. And towards the end of the last century it looked as if the battle was being won.
In 1980 The World Health Organization, under the leadership of D.A. Henderson, declared naturally occurring smallpox eradicated from the face of the earth. It was a monumental declaration since that disease alone had claimed more than 300 million lives in the first 80 years of the 20th century. This is more than three times the number of people killed in all the wars in the world.
Disease has been used on the battlefield from ancient times. Synthian archers dipped their spears and arrows in blood and manure to cause illness in those they pierced and the British gave American Indians blankets infected with smallpox scabs. But recent scientific advances have allowed the manufacture of designer diseases that if deliberately released - especially to a vulnerable and unvaccinated population - could prove disastrous.
Although to date, no one has yet been implicated, the Anthrax attack of 2001, where five people died and 22 were infected after coming in contact with weaponized Anthrax spores, proved to many that the biological weapons could wreck terror on a nation unprepared for such a stealth attack.
While most nations have banned the use of biological weapons through the Biological Weapons Convention of 1972, smallpox officially remains in freezers in the United States and Russia - and many experts believe unofficially in many places in the world.
To learn more about biological weapons watch "Silent Killers: Poisons and Plagues" on your local PBS station.