How Influenza Spreads
Influenza Virus
Understanding the Influenza Virus
How a tiny virus can cause illness.
Type of Influenza Virus
Influenza is caused by a group of viruses called influenza viruses. These viruses infect the respiratory system, including the nose, throat, and lungs. One special feature of influenza viruses is that they can change and mutate over time, which makes the flu difficult to control completely.
Scientists classify influenza viruses into four main types: A, B, C, and D.
Influenza A
Influenza A viruses are the most important type for human health because they can cause large outbreaks and even global pandemics.
Influenza B
Influenza B viruses also infect humans and contribute to seasonal flu outbreaks, but they do not cause pandemics.
Influenza C
Influenza C viruses are less common and usually cause mild illness. Because the symptoms are generally not severe, they are not considered a major public health concern.
Influenza D
Influenza D viruses mainly infect cattle and other animals. At present, they are not known to infect humans, so they are not considered a risk to human health.
Transmission of Influenza Virus
Influenza spreads mainly through respiratory droplets released when infected people cough, sneeze or talk. These droplets can travel through the air and be inhaled by people nearby.
1. Droplet Transmission
When an infected person coughs or sneezes, tiny droplets containing the virus are released into the air. People nearby may inhale these droplets and become infected.
2. Surface Transmission
The virus can survive for a short time on surfaces such as desks, toys, and door handles. When people touch these surfaces and then touch their eyes, nose, or mouth, the virus may enter the body.
3. Close Contact
Crowded places such as schools, public transport, and workplaces increase the risk of transmission because people are in close contact with each other.
