What is the influenza virus?
Influenza virus is an RNA virus that causes seasonal influenza in humans and animals. It causes acute respiratory infections and spreads rapidly through the air, often causing periodic pandemics around the world. Influenza viruses can cause more severe symptoms, such as pneumonia or respiratory failure, in individuals with weakened immune systems, including older adults, children, and immunocompromised patients. The virus was first discovered in 1933 by Wilson Smith and named H1N1. "H" stands for hemagglutinin and "N" stands for neuraminidase. Numbers represent different subtypes.
Influenza viruses are spherical in shape, and new isolates are often filamentous, with a diameter of 80 to 120 nm and a filament length of up to 400 nm. The structure of influenza virus can be divided into three parts: envelope, matrix protein and core.
Depending on the type of organism they infect, influenza viruses can be divided into human influenza viruses, swine influenza viruses, equine influenza viruses, and avian influenza viruses. According to the antigenicity of the nucleoprotein, influenza viruses can be further divided into four types:
- Influenza A virus is widely distributed in animals and can cause a global influenza pandemic.
- Influenza B virus is only found in humans and seals. It often causes local outbreaks of influenza but does not cause a global pandemic.
- Influenza C virus is only found in humans and pigs. It usually appears sporadicly and does not cause large-scale outbreaks.
- Influenza D virus is only found in pigs and cattle, but there have been no reports of human infection.
Influenza A viruses, especially certain subtypes, are highly pathogenic to humans and have caused multiple pandemics around the world. Some avian influenza A virus subtypes, such as H1N1, H5N1, H7N1, H7N2, H7N3, H7N7, H7N9, H9N2 and H10N8, have been found to directly infect humans. Among these subtypes, H1, H5, and H7 are highly virulent, and H1N1, H5N1, and H7N9, in particular, deserve great attention.
Post time: Oct-21-2023