The Mexican swine flu, a genetic chimera probably conceived in the faecal mire of an industrial pigsty, suddenly threatens to give the whole world a fever. The initial outbreaks across North America reveal an infection already travelling at higher velocity than did the last official pandemic strain, the 1968 Hong Kong flu.

Stealing the limelight from our officially appointed assassin, H5N1, this porcine virus is a threat of unknown magnitude. It seems less lethal than Sars in 2003, but as an influenza it may be more durable than Sars. Given that domesticated seasonal type-A influenzas kill as many one million people a year, even a modest increment of virulence, especially if combined with high incidence, could produce carnage equivalent to a major war.