Nov 21, 2006
2:00/1:00 MT/PT
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What is a virus?
How does a virus work?
What is your immune system?

Sick person clipart
  Polio VirusViruses are in the news. You've probably heard about Avian Flu, West Nile Virus, HIV, and SARS. You probably know about chicken pox, measles, rabies, or polio. I'm sure you've had a "cold." Your nose is runny, you sneeze a lot and have a sore throat. Your eyes might be red, and you might feel sore all over and have a fever. A "cold" and many other diseases are caused by a tiny, microscopic living thing called a virus. Photo. Courtesy of the; © Jean-Yves Sgro, University of Wisconsin.

What is a virus? A virus is a microbe. A microbe is a tiny one-celled living organism, too small to be seen with just your eyes. Other types of microbes are: bacteria, protozoa, and fungi. Some people call microbes "germs".    Girl and Microscope 

 Not all microbes are bad... Many bacteria live with us all the time, and help us do amazing things like make yogurt, pickles, cheese, and even break down some garbage. Microbes are all around us. They exist on our skin, and on the skin of fruit.

What is a germ?

Here is a photo of one type of virus.
This photo gallery has even more images.
Discovery of the Virus   
How big is a virus?

Mask over nose and mouthHow does a virus infect you? Viruses are everywhere but they need to get inside a human, an animal or a plant to make them sick. In fact, they must invade a cell, called a host cell, in order to grow and reproduce. Most can't survive long unless they're in a living host. Once inside, though, they can spread and make other people sick. Some can live awhile on something like a desk, or doorknob so it's important for you to wash your hands regularly so you don't become infected! Viruses can enter us through the nose, mouth or breaks in the skin.

     Viruses are made of a small collection of genetic material (DNA or RNA) encased in a protective protein coat called a capsid. Take a peek at what's inside a virus...

Is a virus ALIVE? There is some debate about this. However, most scientists say they are not alive because they cannot grow or reproduce on their own.
They need a host cell to multiply.

Then what happens?
     Once inside a host cell they follow these basic steps in order to fool the host cell into making make copies of the virus that might then infect living organisms. This is called the lytic cycle.

The Lytic Cycle- or how a virus fools a host cell into making more viruses
A virus attaches to a host cell. (All viruses have some type of protein on the outside coat that "recognizes" the proper host cell.) The enzymes make parts for more new virus particles
The virus, or a virus particle, enters or releases its genetic instructions into the host cell The new particles assemble the parts into new viruses.
The injected genetic material gives instructions to the host cell's enzymes The new virus particles leave the host cell, ready to infect other cells
Discover more about viruses, bacteria , protozoa, fungi.

Man blowing nose Your body's Immune System to the rescue!!!
Your body has a defense against viruses. It is called the Immune System.
If a virus makes it past your tough skin, or the sticky mucus and little hairs called cilia lining your breathing tube then this system takes over.

Here's how it works...The immune system is an organization of different types of cells, tissues and enzymes work together to identify and eliminate all invading substances in your body. Each part of the immune system has it's own specialized job.

    Doctor and patient White blood cells are your main defense. They patrol your body. When they come across an antigen, they produce an antibody that only works to fight against that particular antigen. Some antibodies destroy antigens while others make it easier for white blood cells to destroy the antigen.

     Trillions and trillions of white blood cells gobble the enemy. Sometimes, though, your body needs help from the medicines doctors give you. One of these medicines is called a vaccine. Learn about vaccines here.

Did you knowThere are hundreds of different kinds of viruses, and they’re constantly changing. You can't catch the same virus twice. The immune system can remember the response later if the foreign substance invades the body again, and it gets right to work.

Infection, Detection and Protection...

Petri dishWowPlants get viruses, too!!! Here's a photo of a peach tree leaf with a virus!

So you want to be a microbiologist? up on careers in exploring the unseen world.

More about Viruses:    LINKS     GLOSSARY     RESOURCES
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