Meet the Flu Bug

Influenza is caused by a virus—a tiny particle that consists of RNA (genetic material also known as ribonucleic acid) inside a protein coat. The influenza virus, like other viruses, can only reproduce by taking over a "host" cell (a cell that provides nourishment for the virus).

Here is how influenza can spread:
A person who is infected with influenza coughs or sneezes, releasing tiny particles of virus. (This person may not even feel sick at the time.)

Another person in the room may breathe in the viral particles.

The viral particles can then attach themselves to cells in the nose, throat, and lungs of this second person.

Each cell that has been infected by influenza becomes a little "influenza factory," making more virus to infect additional cells.

The damage to the cells in the nose, throat, and lungs can cause the person to cough, thereby helping to spread the influenza virus to other people.

Viral particles that land on doorknobs, telephones, and other surfaces can cause infection if someone picks up influenza on their hands and then touches their nose, mouth, or eyes.

Flu Fact
Many of the symptoms of influenza—fever, chills, and body aches — are really signs that your immune system is working very hard to fight infection. They are caused by cytokines, chemicals produced by activated immune cells.