Avian influenza is a viral infection that can infect not only birds, but also humans and other animals. H5N1 is the most common form of avian influenza, which is deadly to birds and can easily infect humans. H5N1 was first detected in humans in 1997 and has killed nearly 60 percent of people who have contracted it, according to the World Health Organization.

Influenza viruses are constantly changing and mutating. Variant influenza A viruses can infect and cause severe respiratory illness in humans. These influenza viruses are different from the subtypes of influenza A viruses that circulate in humans and include influenza viruses that originate mainly from birds and pigs.

There are four types of influenza viruses: A, B, C, and D. Wild birds—especially wild ducks, geese, swans, gulls, shorebirds, and swallows—are the natural hosts of most influenza A viruses.

Influenza A viruses, also known as avian influenza, have infected many different species of animals, including ducks, chickens, pigs, whales, horses, and seals. However, some influenza viruses are specific to certain species, with the exception of birds, which are hosts to all known influenza A viruses. So can avian influenza infect humans?