What Is a Virus
A virus is microscopic living matter that relies on a host to reproduce and survive. The virus will cause physical effects that result in the diseases that affect us daily throughout the world. Since the makeup of a virus is so simple in its makeup, it must rely on host cells for the machinery needed to survive and reproduce.
How a Virus Finds a Host
Before a virus can reproduce, it must find a host cell, and viruses accomplish this in a variety of ways. Some viruses are airborne, such as the cold and flu viruses, and will infect a host and its cells through the mouth or nose. Other viruses need to be specifically injected or ingested into the host either through sexual intercourse, hypodermic injection or simple things like kissing or ingesting other bodily fluids through the mouth.
How a Virus Reproduces
Once the virus has found a host, it looks for host cells to take over. The virus slowly implants its genetic makeup into the cell. At that point the virus can either lie dormant--such as in some cases of the HIV/AIDS virus--or immediately start reproducing. Instead of the virus splitting and reproducing in that manner, the virus implants its genetic makeup into the hosts cell. As the host cell reproduces, its replicates have the genetic makeup of the virus instead of the original cell. The virus continues like this until stopped by the host's immune system or until the host dies.