Avian flu, also known as bird flu, is a disease caused by infection with avian influenza A viruses. These viruses are primarily found in birds, including wild aquatic birds worldwide and domestic poultry. Bird flu viruses do not normally infect humans, but sporadic human infections with bird flu viruses have occurred. Human infections with bird flu viruses can happen if enough virus is inhaled or gets into a person’s mouth, eyes, or nose. Symptoms in people can range from mild upper respiratory tract infection (fever and cough) to severe pneumonia. There are different subtypes of avian influenza viruses, and some of them have caused serious illness and death in humans. However, human-to-human transmission of bird flu viruses is rare. The disease has devastating effects on the poultry industry, threatening workers’ livelihoods, food security, and international trade. Reporting suspected cases of bird flu in birds is important, and bird flu is a notifiable disease in poultry and other captive birds. Signs that a bird may be infected with bird flu include sudden death, swollen head, closed and runny eyes.