swine flu
Caused by influenza type A virus, there are regular outbreaks among herds of pigs, where the disease causes high levels of illness but is rarely fatal.
It tends to spread in autumn and winter but can circulate all year round.
There are many different types of swine flu and like human flu, the infection is constantly changing.
Swine flu does not normally infect humans, although sporadic cases do occur usually in people who have had close contact with pigs. Read more swine flu