The human body can be infected by a variety of different foreign substances.
These include infections as deadly as a virus, or as common as common as a bacterially
infected wound. Once a human is infected with anything foreign the immune system
immediately begins fighting the foreign substance. However the immune system cannot
usually kill the entire foreign cells, a few often survive. However this number is
so few a person can hardly claim to be sick or infected. Although that person is now
a carrier. A carrier is some one who is infected, or has some of a particular
foreign substance in him, yet shows no symptoms. That person could pass on the
pathogen or virus without even realizing it.
 Viral infection occurs when a virus enters a host, in this case a human host,
and begins to use the host cells to replicate. The virus will attach it self to a
host cell and inject its viral DNA into it. The viral DNA quickly takes over the
healthy host DNA and virus replication begins. If the virus is not stopped it will
take over all the host cells.
 Bacterial infection occurs as a pathogen enters a human. The
pathogen does not use the human cells as a host as the virus does, but it begins to kill
them. A bacterial infection is easier to treat because the bacteria can be
killed. However for a virus to be killed the host cells must be killed also.
defense lymph
infection
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