There is something biblical about modern farming. One calamity seems to follow another. Plagues sweep through livestock with terrifying speed. Barely had we got used to television images of sick cows, staggering with BSE, than our screens filled with the pyres of thousands of dead animals, incinerated in an attempt to stop the spread of foot and mouth.

The numbers are barely comprehensible by anyone not involved in the industry. Foot and mouth saw the destruction of seven million sheep and cattle (quite unjustifiably, but that's another story). Avian flu, which has now been diagnosed on one of Bernard Matthews's turkey farms in Suffolk, could, if it takes hold in poultry farms across Britain, be equally devastating. The one infected farm holds 160,000 birds. They will all have to be slaughtered. Frogs, locusts and boils could hardly be worse.

Except that there is something worse. The H5N1 strain of bird flu could, as may have happened with BSE, leap the species barrier. Indeed, in a statistically small number of cases, this has already happened: 164 people have died from the human form of the disease since 2003. The official word for a disease which originates in animals but is passed to humans is zoonosis.