Microbes & Diseases II

Protecting ourselves against diseases

Your body has several ways defends itself against micro-organisms.

·         Sweat and tears contain an enzyme that kills bacteria.

·         Hairs in your nostrils trap micro-organisms and mucus contains enzymes that can kill bacteria.

·         Enzymes in saliva can kill bacteria.

·         Most bacteria swallowed with food and drinks are killed by acid in the stomach.

But microbes get past these defenses

Tuberculosis (TB) is a serious disease that destroys lung tissue.

TB comes with a bad cough and each time a person with TB cough, they spray little droplets into the air. These droplets contain TB bacteria.

If you are nearby, you can breathe them in.

What happens when you catch a cold

Several different viruses cause colds. When you have a cold and sneeze, you spray several droplets of liquid into the air. Each droplet contains thousands of viruses.

When you first catch a cold, the virus multiplies very quickly. You begin to feel ill, with a runny nose, sore throat and a cough.

Your body starts to fight back the invasion; cold viruses are destroyed and you start to feel better.

How your body destroys microbes

Your blood contains red blood cells and white blood cells. There are two different types of white blood cells.

1.      One type of white blood cell engulfs (traps) microbes and destroys them.

 2.      Another type of white blood cell makes disease-fighting substances called antibodies. These can stop microbes from causing disease.

Each antibody that you make is specific to fighting one type of microbe.

An antibody won’t work against any other type of microbe.

Different microbes need different antibodies. It takes time for your body to make these different antibodies, and you feel ill until you have enough antibodies to destroy the microbes.

Once you have had a disease, your white blood cells have learnt how to make the antibodies. They will be able to make the right ones much more quickly in the future.

If a second attach comes, your body can destroy the microbes before they have time to make you ill. This means you are immune to the disease. You have immunity.

Active immunity

This happens when people make their own antibodies to a disease.

Natural: if you have been infected with a disease, your body made antibodies to destroy it. Your body remembers the disease, and is ready to make antibodies quickly if you were ever infected again.

Artificial: you can be injected with a vaccine containing weakened or dead microbes, or some bits of microbes. The active live microbes are not present, so the vaccine does not make you ill. But your body reacts to the microbes and sets about making antibodies to fight them. It then remembers how to make these antibodies, ready to react if you are ever infected with the disease.

Passive immunity

With passive immunity, people are given ready-made antibodies.

Natural: pregnant women pass on their antibodies to their growing baby through the placenta.

There are also antibodies in breast milk. This gives newborn babies some immunity from microbial infections.

Artificial: antibodies are made outside the body, for example in the laboratory. These antibodies are injected into people and animals to give protection from fast-acting microbes. An example is the anti-tetanus vaccine. You may be injected with this if you have a deep or dirty wound where tetanus bacteria may grow. Your body may not make its own antibodies fast enough to fight.

Immunisation is a very effective way of preventing an epidemic, when a disease spreads through the population.

Vaccines only work if lots of people are immunised.