Invisible Threat examines the history of humans developing and using bio weapons - primarily the Japanese, the Americans, the Soviets, the British and the Canadians. It also explores the possible fallout from this massive military endeavour. Although states now have laws now prohibiting the use of these weapons, the Internet allows small groups of people and individual operators access to toxic recipes and the means by which to use them. And we are already seeing such attacks in countries like the US, and there are still those who believe the E.coli outbreak in Europe in 2010 was intentional. What is frightening to me is that in its rush to stockpile cures for outbreaks of pathogens, science has created new strains in labs that are subject to human failings - either by accident or intentionally. I love to travel and, like most people, I sometimes hesitate to place a hand on a much-used railing in a public stairway or have felt the uncomfortable press of people packed into a subway car. Nature's pathogens can spread so easily, so rapidly. And what is worse is that humans are capable of terrorising and killing using these invisible, ordourless weapons - we only need to look back at our history to substantiate this argument. By Gerald Sperling