November 23, 2012 11:18 am

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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 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.
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.
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.
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.
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.
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.
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.
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