How is Influenza Spread?

Transmission of Influenza

Viruses are very tiny particles that cannot grow or reproduce outside of a host cell; they must use the cell machinery of their host (e.g., person, animal, or plant) to grow and reproduce.   Viruses are made up of genetic material (DNA or RNA) and proteins that give them structure.  The Influenza virus is a virus made up of RNA and different proteins.  (Some of these small protein pieces are called hemaglutinin and neuraminidase, which is what the H and N stand for if you hear, for example, H5N1 mentioned in the context of avian or pandemic flu.)

A virus can enter your body in multiple ways.  For example, people may touch a virus on an inanimate object like a doorknob, then touch their mouth or nose and transfer the virus there.  Most people believe that influenza is transmitted within large droplets of moisture that are expelled from the mouth when a sick person coughs or sneezes.  If you are in proximity to these droplets, you can breathe them in and they can then enter your respiratory tract.  Once the droplets containing influenza virus enter your body, the influenza virus can attach to the cells of your respiratory tract and infect them.  Viruses use the cell machinery to reproduce and create many copies of the same virus that then spread to other cells of the body.  The host immune system usually comes across pieces of viral protein that it recognizes as “foreign” and mounts an immune response to the viral invader.  However, it takes a few days for the immune system to build up, which is why most people develop symptoms of an illness before their body is able to fight off the infection.

Once the virus has replicated that person is then infectious and can potentially transmit the virus to other people.  When the infected person coughs or sneezes, viruses in his or her respiratory tract are then part of the large droplets of moisture expelled, which can then enter another person – and the cycle continues!

Point of story: cover your coughs and sneezes with your sleeve (or cough into a tissue, then clean your hands) when you are sick so others around you do not get exposed to the virus causing your illness!