Concerns have been raised that highly pathogenic avian influenza, sometimes known as bird flu, could move to humans and become a new pandemic after infecting hundreds of people and spreading to mammals.
Mammal cases of the disease have primarily been found in Europe and the Americas.
The UK government announced on Monday that the first case had been found at a farm in northern England, adding sheep to the list.
While some mammals, like sheep and dairy cows, are raised and so have direct contact with people, increasing the risk of transmission, other mammals have far less interaction.
