Viruses
Have you ever scratched your skin and wondered what you are made from? If you could look at the surface of your skin through a microscope you would see that it appears to be covered with microscopic paving stones. They spread out over the surface like the paving stones in a town square. Each paving stone is really a dead cell. If you were to pull one up, you would find another below it. If you pulled up this cell you would find another. You could burrow into the skin by removing one cell after another. You would find that as you went deeper into the skin, the cells became thicker and contained more liquid. Eventually you would reach living cells. There are billions of living cells in the body and they are the targets of viruses.

You could think of a virus attack by thinking of yourself as a body cell. There are three main parts to a body cell. These are the outer skin, a juice full of chemicals to keep you alive and a store of instructions to control how the chemicals work. The instructions are in the form of a chemical too. This chemical has a complicated name but is usually called DNA. The DNA is stored in an oval structure inside a cell. This structure is called the nucleus. One way to think about the structure of a cell is to think of a transparent beach ball with a rugby ball inside it. The beach ball forms the cell skin, the rugby ball forms the nucleus and the rest of the space inside the beach ball would be occupied by the cell's juice.

Imagine that you are a healthy cell. You are sending out messages from your nucleus to control the chemicals. The chemicals are working together to make substances to keep you alive. They are also making substances to help you grow and repair yourself. Food and oxygen enter through your skin from the blood and release energy to keep the chemicals working. The carbon dioxide that is produced when the energy is released passes out through your skin to be carried away by the blood.

Now imagine that you are attacked by a virus. If you imagined the cell to be the size of a beach ball then a virus is about the size of a table tennis ball. The shape of a virus varies greatly. Some have simple shapes like an oblong block while some can look like spacecraft, complete with spikes sticking out of them. Imagine that the virus that attacks you looks like an oblong cardboard box. It pushes its way through your skin into the chemical juice. Immediately the box opens and out shoots a coiled thread. This is viral DNA. It sends out messages to your chemicals. They stop working for you and start working for the viral DNA. The chemicals use the instructions from the viral DNA to make more viral DNA. Soon the cell juice is starting to fill with threads of viral DNA. Each new thread of viral DNA starts sending out its own messages. These command more of your chemicals to set to work. These chemicals build a case for the viral thread and before long the virus is complete - a DNA thread inside a case.

By now the cell you were is no more. The viruses have used up your chemicals and stopped your life processes. As your skin breaks open the viruses leave like a squadron of aircraft to attack more cells. The attack that occurred in your cell will be repeated many times and a disease may develop but viruses do not have it all their own way. The body has a defence system against harmful microbes and the chances are it will soon swing into action and destroy the viruses before their numbers get too large.

Where are viruses found outside the body?
Like other microbes they can be found almost everywhere. In the soil, on surfaces, in the air and in water.

What do viruses live on when they are outside the body?
They do not live on anything. They just wait for a chance to infect a body. It is only then that they can make copies of themselves and breed.

Is a virus a living thing?
Not really. A living thing has seven features of life. These are feeding, respiring, excreting, growing, moving, breeding and responding to changes in the surroundings. When a virus is outside the body it does none of these things. In fact viruses can be stored in jars just like crystals of salt or sugar. When the virus is in the body it only breeds and this is just a process in which the DNA is copied. It does not even grow its case. The cell makes that for it.

What does DNA stand for?
It stands for deoxyriboneucleic acid. This is a substance that is found in the nucleus of every cell. It contains instructions on how the cell should grow and keep healthy. It also contains all the instructions for how the body should develop. It even controls how the body grows and the features of your face and fingerprints. In fact a sample of DNA taken from the cells inside your mouth can be used to identify you in the same way that your fingerprints can be used.

What diseases can viruses cause in humans?
They can cause colds, influenza, chicken pox, mumps, measles and smallpox. A virus also causes cold sores.

Can viruses cause diseases in animals?
Yes, they can. A virus is responsible for the foot and mouth disease that can attack cattle, sheep and pigs. Rabies is a disease which dogs can catch and this can be passed to a person if he or she is bitten by a rabid dog. A virus causes myxomatosis, which is a disease of rabbits.

What happens when a person gets rabies?
The virus attacks the cells in the brain and the spinal cord. The speed at which the disease develops depends on how badly a person was bitten. Sometimes the disease may develop after about thirty days but it may be longer. At first there may be headaches and sickness, then the muscles fail to work properly and food and drink cannot be swallowed. As the body fails to take in the water that it needs a great thirst develops. When this stage is reached a person has not long to live. A person who thinks they may have been bitten by a rabid dog can have daily vaccinations for a few weeks. This may help them survive the disease.

Do viruses attack plants?
Yes, some viruses do. There is a virus which attacks the tobacco plant. It causes the plant to grow poorly and to develop mottled leaves. A virus attacks tulips and gives their petals attractive streaks.

How can the body destroy viruses?
Microbes such as bacteria and viruses have substances on their bodies called antigens. The body responds to the presence of an antigen by making an antibody to match it. The antibody and antigen fit together like a lock and key. When an antibody attacks a virus it makes the virus harmless or completely destroys the virus. Antibodies can only work on viruses when they are on their way between cells. They cannot work on viruses inside cells.