If flu viruses have favoured hook-up spots, then pig pens would be high on the list. Their airways contain molecules that both bird flu viruses and mammalian flu viruses can latch onto. This means that a wide range of flu strains can infect pigs, and if two viruses infect the same cell, they can shuffle their genes to create fresh combinations.

This process is called reassortment. In 2009, it created a strain of flu that leapt from pigs to humans, triggering a global pandemic. If we needed proof that pigs are “mixing vessels” for new and dangerous viruses, the pandemic was it.

Now, scientists have found a new strain of flu in Korean pigs that remphasises the threat. It’s an