About Viruses

Viruses are very small living particles. This section reviews information about viruses that will help you understand the H1 N1 flu virus.

Viruses are made of an outer shell that protects genetic material packaged inside. In order for a virus to reproduce, it needs to enter a living cell by attaching itself to the living cell's surface. Viruses tend to infect only specific cells in a specific species. For example, certain viruses may only attack human cells while others can attack only bird cells.

Once inside the cell, the genetic material of the virus blends with the genetic material of the infected cell and copies itself hundreds, if not thousands of times.

The hundreds of copied viruses then kill the cell, burst out of it, and infect many new cells. The cycle repeats itself and can make a person very sick unless the person's immune system destroys the virus. The immune system is responsible for defending the body against viruses.

When a virus is copying itself, the genetic material of the virus can go through changes known as 'mutations'. The virus can also exchange genetic material with the infected cell which can modify the surface of the virus. This may make it possible for the virus to attack the living cells of different species such as pigs and humans. A virus modified by mutation is known as a different strain.

There are three types of influenza viruses, A, В and С. Types В and С are usually only found in humans. Type A can be found in both humans and animals such as birds, pigs, horses, whales, and seals.