Sick birds pass the virus out of their bodies in their droppings. As these dry they can be trampled on by people or other birds. The droppings are ground into a dusty powder and if humans breathe in the dust they might get bird flu.

The last outbreak of Bird flu in was in 1997. Back then 18 humans caught it. They had all been very close to live chickens that were carrying the virus. They all worked on farms or had been to markets where live animals were for sale.