For example, in late 2016 to early 2017, an avian H7N2 strain was found to be infecting cats in New York.Equine IAVs include H7N7 and two lineages of H3N8. H7N7, however, has not been detected in horses since the late 1970s, so it may have become extinct in horses. H3N8 in equines spreads via aerosols and causes respiratory illness. Equine H3N8 perferentially binds to α-2,3 sialic acids, so horses are usually considered dead-end hosts, but transmission to dogs and camels has occurred, raising concerns that horses may be mixing vessels for reassortment. In canines, the only IAVs in circulation are equine-derived H3N8 and avian-derived H3N2. Canine H3N8 has not been observed to reassort with other subtypes. H3N2 has a much broader host range and can reassort with H1N1 and H5N1. An isolated case of H6N1 likely from a chicken was found infecting a dog, so other AIVs may emerge in canines.Other mammals to be infected by IAVs include H7N7 and H4N5 in seals, H1N3 in whales, and H10N4 and H3N2 in minks. Various mutations have been identified that are associated with AIVs adapting to mammals. Since HA proteins vary in which sialic acids they bind to, mutations in the HA receptor binding site can allow AIVs to infect mammals.
Influenza viruses, particularly IAV, evolve quickly, so flu vaccines are updated regularly to match which influenza strains are in circulation. Vaccines currently in use provide protection against IAV subtypes H1N1 and H3N2 and one or two IBV subtypes. Influenza infection is diagnosed with laboratory methods such as  antibody or antigen tests and a polymerase chain reaction (PCR) to identify viral nucleic acid. The disease can be treated with supportive measures and, in severe cases, with antiviral drugs such as oseltamivir. In healthy individuals, influenza is typically self-limiting and rarely fatal, but it can be deadly in high-risk groups. In a typical year, 5–15% of the population contracts influenza. There are 3–5 million severe cases annually, with up to 650,000 respiratory-related deaths globally each year. Deaths most commonly occur in high-risk groups, including young children, the elderly, and people with chronic health conditions. In temperate regions of the world, the number of influenza cases peaks during winter, whereas in the tropics influenza can occur year-round. Since the late 1800s, large outbreaks of novel influenza strains that spread globally, called pandemics, have occurred every 10–50 years. Five flu pandemics have occurred since 1900: the Spanish flu in 1918–1920, which was the most severe flu pandemic, the Asian flu in 1957, the Hong Kong flu in 1968, the Russian flu in 1977, and the swine flu pandemic in 2009. Signs and symptoms
The time between exposure to the virus and development of symptoms, called the incubation period, is 1–4 days, most commonly 1–2 days. Many infections, however, are asymptomatic.