Your throat is sore. Your nose is running. You shiver from the chills.

There's no doubt about it: You have a microbe.

Yes, your fever and upset stomach, your aching muscles and your sleepy days are all caused by something so small you can't see it with the naked eye - and you need a pretty powerful microscope to even catch a glimpse.

A microbe - the tiniest of all organisms - is a general name for things like bacteria and viruses, the germs that make us say .....AAAAHHHCCHHOOOOOOO!

What is a bacterium?

Bacteria (the word for more than one bacterium) are some of the oldest forms of life on Earth and can be found everywhere.

They are made of a single cell that contains genetic material called DNA. They also have ribosomes, a copy machine for their DNA. They protect their insides with a cell membrane and a cell wall, but not much else.

Bacteria, like viruses, can cause disease, but not all bacteria are bad. In fact, some bacteria are necessary for life. E. coli lives inside you, helping you digest your food. Other bacteria turn milk into yogurt and cheese, help make antibiotics and clean waste from water.

When a bacterium does cause an infection, your body reacts with its usual defense mechanisms: fever, swollen glands and a lot of antibodies. Sometimes antibiotics are given to help your body.

What is a virus?

A virus is a tiny microbe made of a protein shell and some genetic material - either DNA or RNA or both. It's a pretty simple germ.

But it's this tiny, basic "bug" that causes everything from the flu to colds to Ebola, a disease that causes bleeding. In fact, a virus can cause any number of conditions when it infects a cell.

Viruses infect cells for one reason: to make more viruses. Viruses need living cells to make more of themselves. They use the living cell to copy the genetic information kept inside the virus. That information forms more viruses. The living cell is essentially a virus factory. Sometimes they destroy the factory when they're done with it - the cell bursts and the viruses move on to the next cell. When the virus uses the "factories" and destroys them, that's when infection occurs.

That's about the time fever, coughing and sneezing may start - all to help fight the infection. The fever is one way your body fights infection by making it uncomfortable for the virus to be there. When you cough and sneeze your body is trying to rid itself of the virus.

Some viruses are prevented with vaccine shots that make your body get ready to fight the virus before infection. But your body is in charge of getting rid of most viruses - sometimes aided by sleep and a bowl of soup.