Different versions of bird flu have been spreading around the world in recent years.
The virus, officially known as H5N1, is believed to have killed millions of wild and domestic birds worldwide. Some other animals have also been infected.
The virus infected a very small number of people as well. But, H5N1 largely has remained outside the human population. Most of the few human cases involved direct contact between people and infected birds.
Reuters news agency recently explored areas of the world where versions of H5N1 have infected humans.