health

Viruses can cause illness by destroying or interfering with the functioning
of large numbers of important cells. Sometimes, as mentioned earlier, the
cell is destroyed when the newly created viruses leave it. Sometimes the
virus keeps the cell from producing the energy it needs to live, or the virus
upsets the cell’s chemical balance in some other way. Sometimes the virus
seems to trigger a mysterious process called “programmed cell death” or
apoptosis (ap-op-TO-sis) that kills the cell.
Some persistent or latent viral infections seem to transform cells into
a cancerous state that makes them grow out of control. It has been estimated
that 10 to 20 percent of cancers are caused by viral infections.
The most common are liver cancer caused by persistent infection with
hepatitis B or hepatitis C virus and cancer of the cervix (the bottom of a
woman’s uterus or womb), both of which are linked to certain strains of
the human papillomavirus.
Sometimes a viral illness is caused not by the virus itself, but by the
body’s reaction to it. The immune system may kill cells in order to get rid
of the virus that is inside them. This process can cause serious illness if
the cells being killed are very important to the body’s functioning, such as
those in the lungs or central nervous system, or if the cells cannot reproduce
quickly enough to replace the ones being destroyed.