Viruses (vy-rus-iz) are very tiny micro-organisms.
Viruses are even smaller than bacteria.
Viruses can only grow and reproduce inside their hosts.
Humans, animals and plants are their hosts.
Most viruses cannot live long outside their hosts.
Some viruses can spread very fast inside our body.
They can make us sick.
Measles, chicken pox, polio, mumps and flu are caused by viruses.
H1N1 virus causes Influenza A(H1N1).
AIDS is caused by HIV virus.
Viruses can also make plants and animals sick.
Viruses also effect bacteria.
Anyway viruses that effect plants cannot effect animals and human.
Viruses that effect human cannot effect plants and animals.
We use viruses to make vaccines.
Vaccines help our body to fight diseases.
Anyway these viruses are not the same as computer virus.
Computer viruses are not living things.