Influenza A virus (often referred to as influenza A) is aflu virus, including a variety of subtypes, can infect various mammals such as wild birds, domesticated poultry, pigs, horses and humans. The virus is orthomyxoviridae, the only one under the influenza A virusspecies. Strains of all subspecies of influenza A virus have been isolated from wild birds, but the birds themselves rarely get sick. Some influenza virusisolate can cause disease in poultry and a small number of humans. The virus can sometimes infect poultry from wild waterfowl, which can cause outbreaks of influenza plague in humans.

Vaccines for the swine flu virus have been developed, and many countries are hoarding them to respond quickly to bird flu outbreaks. In 2011, researchers reported the discovery of antibodies effective against all subtypes of influenza A.

Famous influenza epidemics in history were all caused by influenza A viruses, including 1918 Spanish flu, 1957 Asian flu, 1968 Hong Kong flu, 1977 Russian flu, 2003 H5N1 bird flu, 2009 H1N1 flu, 2013 H7N9 flu, etc.

Subtype

Influenza A virus particles are spherical or filamentous, about 80-120 nm in diameter, and have a capsular. The structure of influenza A virus is divided into three layers, the outermost layer is a double lipid vesicle membrane; the middle layer is the matrix protein M1, forming a spherical protein shell; the inside is nucleocapsid, helical symmetry, including nuclear protein, two polyenzyme proteins and viral genome single-chain RNA. There are three protein protrusions on the surface of the virus, which are hemagglutinin(H), which acts like a key to help the virus open the door to the host cell; Neuraminidase(N), a receptor capable of destroying cells, allowing the virus to spread freely in the host. The classification and naming of influenza A virus subtypes are based on these two names. 18 hemagglutinins (H1 to H18) and 11 neuraminidase (N1 to N11) have been identified so far, so theoretically there are 18 × 11 = 198 different arrangements of influenza A virus subspecies combination. The singular subtype is more contagious. In addition, each subtype hasmutationinto different strains, and the pathogens are not the same. Some pathogens are unique to one influenza A virus, while others are shared by several influenza A pathogens.

Human influenza virus

"Human influenza virus" generally refers to a subtype that spreads widely among humans. Among them, H1N1, H1N2, and H3N2 are currently known influenza A viruses that can be transmitted between humans.

Influenza in humans usually causes fever, cough, sore throat, muscle ache, conjunctivitis, and severe cases may even have breathing problems and fatal pneumonia. The severity of the infection is mainly related to the immune system and if the infected person has been previously exposed to the virus strain, then the infected person will have partial immunity.

However, the highly pathogenic H5N1 avian influenza will bring very serious consequences to humans, with a fatality rate of 50% after infection. It has been reported that a boy with H5N1 fell into a coma immediately after showing diarrhea symptoms and completely showed no flu symptoms such as the usual respiratory discomfort.