Influenza a意思

"Influenza A" refers to one of the types of influenza viruses that can cause influenza, or flu, in humans and other animals. Influenza viruses are classified into three main types: A, B, and C. Influenza A viruses are the most common cause of flu epidemics and pandemics.

Influenza A viruses are further subdivided into different subtypes based on the proteins that stud their surfaces: hemagglutinin (H) and neuraminidase (N). There are 18 different known H subtypes and 11 known N subtypes, which can combine in different ways to create different influenza A virus strains.

Some influenza A viruses, such as H1N1 and H3N2, are regularly found in people and can cause annual flu epidemics. Other subtypes, such as H5N1 and H7N9, typically infect birds but can sometimes cross the species barrier to infect humans, often leading to severe disease. These are known as avian influenza viruses.

Influenza A viruses can also infect other animals, including pigs, horses, and seals, and can sometimes be transmitted to humans, causing zoonotic infections. The emergence of a new influenza A virus subtype that can infect humans and spread easily from person to person can lead to a flu pandemic.