Viruses are in the news. You've probably heard about Ebola, 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. Turns, out, a “cold” and many other diseases are caused by a tiny, microscopic living thing called 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.”
Not all microbes are harmful. For example, many bacteria live with us all the time and help us do amazing things like make yogurt, pickles, cheese, and even break down garbage. Microbes are all around us. They exist on our skin and on the skins of fruit and vegetables. Learn more about different types of microbes here.
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 you, 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.
The Lytic Cycle
Once inside a host cell, viruses follow some basic steps in order to fool their host cells into making more viruses. These steps are called the lytic cycle.
A virus attaches to a host cell. All viruses have some type of protein on their outside coats that “recognizes” the proper host cell for its type.
The virus, or a virus particle, penetrates the host cell and releases its genetic instructions into the host cell.
The injected genetic material gives instructions to the host cell's enzymes.
The enzymes make parts for more new virus particles.
The new particles assemble the parts into new viruses.
The new virus particles leave the host cell, ready to infect other cells.
Viruses exist only to reproduce — to make copies of themselves. And they're very good at what they do!
Immune System to the Rescue!
Fortunately your body has a defense against viruses. It is called the immune system. If a virus makes it past the barriers your body has — 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 working together to identify and eliminate all invading substances in your body.
Each part of the immune system has it's own specialized job. 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 antigens. Sometimes, though, your body needs help from the medicines doctors give you. One of these medicines is called a vaccine.
A vaccine is a tiny, weakened, or dead part of a germ that is injected into your body like a medicine. It's not a whole or live germ because a vaccine is not trying to make you sick. Instead, it's just enough of a germ to get the body's immune system revved up and producing lots of antibodies. So if and when the real germ shows up, there will be lots of antibodies already in place to guard your cells from harm.
Did You Know?
There are hundreds of different kinds of viruses, and they're constantly changing. It's unlikely that you'll get sick from the same virus twice. That's because the immune system can remember its previous response to a virus attack, and if that foreign substance invades the body again, the immune system gets right to work. Here's a more complete answer to whether you can get sick from the same virus twice.
Plants get viruses, too!!! Here's an introduction to plant viruses along with some photos.
You want to be a microbiologist? Read up on careers in exploring the world of tiny organisms.