Virus
When you wake up with the sniffles
not feeling too well, you probably have a cold. Colds are caused by viruses.
Other viruses cause the flu and some very serious illnesses such as chicken pox,
measles, rabies, and AIDS. Scientists think viruses might also be a cause of
some cancers. Many viruses can go from one person to another.
A TINY GERM
A virus is a tiny germ that can
infect the body. Different kinds of viruses can also infect animals and plants.
There are thousands of kinds of viruses. There are about 100 kinds of viruses
that cause colds.
Viruses are much too small for
scientists to see even with an ordinary microscope. Scientists must use a
powerful electron microscope to see viruses.
A virus is a pretty simple thing.
It has two basic parts. It has an outer part called a protein coat. Inside the
coat, it has genes. Genes are tiny structures that tell plants and animals how
to grow and what shape to be.
A VIRUS ATTACKS
Each kind of virus infects, or
attacks, a different type of cell. All parts of your body are made of units
called cells. Cold viruses head for the lining of your nose or throat. Sometimes
the cold virus spreads to the air passages that lead to your lungs.
When a cold virus gets into your
nose cells, it tries to take over. First, it takes off its protein coat. Next,
it lets its genes go free. The genes command your nose cells to make more of the
virus. The virus actually uses part of you to make copies of itself.
WHY DO YOU FEEL SICK?
More and more viruses grow in the
cells that make up the lining of your nose. They burst out of one nose cell and
head for other nose cells. This is how the infection spreads.
An infected nose cell dies after
the new viruses burst out. As your nose cells die, your head feels stuffy. Your
nose starts to run. Dying cells make you feel sick.
HOW DO VIRUSES SPREAD?
You can give your cold virus to
someone else. You send out viruses when you cough or sneeze. Another person can
breathe in the virus from the air near you. The virus gets on your hands when
you blow your nose. Other people can get the virus by touching what you have
touched and then touching their nose, eyes, or lips. You can help keep a cold
virus from spreading by covering your mouth when you cough or sneeze. You should
also wash your hands often.
Different viruses spread in other
ways. The rabies virus is in the saliva (spit) of an infected dog. The
dog spreads the virus when it bites. Mosquito bites can also spread viruses.
West Nile Virus goes from birds to mosquitoes when the mosquitoes bite the
birds. The mosquitoes then spread the virus when they bite humans and other
animals.
The virus that causes AIDS is in
blood and other body fluids. The viruses that cause cold sores and chicken pox
get in through the skin. Other viruses live in food and get into people who eat
the food.
FIGHTING A VIRUS
When a cold virus attacks, your
body fights back. Your body sends special white blood cells up to your nose.
These cells are part of your immune system. The immune system cells kill the
virus. After a few days, you get over your cold.
The immune system cannot kill
every kind of virus. The viruses that cause cold sores and chicken pox hide in
nerve cells. The immune system cannot find them there. Some viruses can kill
people. The AIDS virus and the rabies virus are germs that can kill people.
There are no drugs that can cure a
disease caused by a virus. Antibiotics do not kill viruses. Antibiotics only
kill other kinds of germs called bacteria.
Scientists are trying to make
drugs that will kill viruses. They have made some drugs that help control
viruses. Some of these drugs help people with AIDS stay alive.
PREVENTING INFECTION
Doctors use a type of medicine
called a vaccine to keep some kinds of viruses from making people sick. Vaccines
often have dead or weakened viruses in them. There are vaccines for measles,
chicken pox, rabies, flu, and other diseases caused by viruses.
All vaccines work pretty much the
same way. You will not get measles, for example, if you get the measles vaccine.
A doctor or nurse gives you a shot of the vaccine. The vaccine puts the measles
virus into your body. The vaccine virus is too weak to cause measles, but your
immune system does not know that. Your immune system attacks. It learns how to
destroy the measles virus. If a real measles virus later gets into your body,
your immune system will remember how to defeat it. It will wipe out the virus
before it takes over your cells.
USING VIRUSES
Scientists are studying ways to
use viruses as tools. They think of cells infected by viruses as being like
little factories. They want to use viruses to force cell factories to make
chemicals used in medicines.
Viruses may also be able to help
treat diseases caused by missing or damaged genes in humans. Harmless viruses
could carry healthy genes into cells. The healthy genes might cure the
disease.
Some kinds of cancer might one
day be cured by viruses. Scientists may learn how to make special killer viruses
that would attack cancer cells.
