Influenza is an acute respiratory infectious disease caused by influenza virus, which can cause many complications such as myocarditis, pneumonia and bronchitis. Because influenza virus is highly contagious, it is easy to spread, and even there is a worldwide epidemic. China is a country with frequent influenza, and the three world pandemics since 1957 all originated in China.
1917-1919, the flu broke out in Europe, killing 20 million people, the worst flu outbreak in history, and the death toll in World War I was only 8.5 million. Influenza viruses are divided into three types: A, B and C, and they do not have exactly the same antigen, but they can infect people. A is the most popular, followed by B, and C rarely causes popularity.
According to the antigenicity of its nucleoprotein, influenza viruses can be divided into four categories:
1, influenza A virus, also known as influenza A virus, is widely distributed in animals and can cause worldwide influenza epidemic.
2. Influenza B virus, also known as influenza B virus, is only found in humans and seals. It often causes local influenza outbreaks and does not cause global epidemic influenza.
3. Influenza C virus, also known as influenza virus, is only found in humans and pigs. It appears in scattered form and generally does not cause epidemic.
4. Influenza D virus, also known as influenza D virus, is only found in pigs and cattle, but no one has been reported to be infected.