The influenza or flu occurs when a virus infects the upper respiratory system, which includes your nose, throat, and lungs. There are three main types of viruses that can cause the flu: influenza type A, influenza type B, and influenza type C. Each of these types can be found in both humans and animals. The virus largely responsible for most cases of the flu is the influenza type A virus, which can be further divided into subtypes.
The flu is a very contagious illness because it can be spread from person to person in three ways:
- coming into direct physical contact with an infected person (i.e. hand shake)
- touching a surface that has been infected with the virus (i.e. door knobs, telephone)
- breathing in tiny, droplets from the air released by an infected person who has just coughed or sneezed.
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