When a harmful bacterium or virus enters the body it may take the body some time for the body to detect it. During this time the microbes can breed and produce such large numbers that they cause disease. The body has ways of defending itself but it can also be helped by disinfectants, antiseptics, medicines and vaccines.

Bacteria can be found wherever there is rotting material. In fact many bacteria feed on rotting plant and animal material and do not cause disease but other more harmful bacteria may be present with them. Any unwanted food that is not cleared away safely can be a danger to health. All kitchen scraps must be stored in a sealed bin. They should not be left around either inside or outside the home. Disinfectants are chemicals which can kill germs and they should be used to treat toilets, drains and any other places where harmful germs may gather. Disinfectants are powerful chemicals and must be used with great care.

The skin is bombarded with many tiny particles during the day. Some of them could be bacteria and viruses. If the skin is cut these microbes will quickly invade the body. Their attack can be stopped by applying an antiseptic liquid or ointment to the wound. The antiseptic contains chemicals which kill germs without damaging the body. It is also important to wash the skin regularly (using soap as well as water) so germs cannot build up on it and wait there for a chance to invade.

When germs have entered the body there are ways to attack them. Bacteria remain outside the body cells and can be attacked by substances called antibiotics. These kill the germs and remove the infection. Viruses, however, cannot be treated with antibiotics because they enter the body cells where the antibiotics will not work. Viruses can be attacked by antiviral drugs.

The body has its own defence system. It responds to substances on the germs called antigens. The body makes antibodies to attack the germs carrying the antigens. Each kind of germ has a different antigen so the body produces different antibodies to fight each different kind of germ. When the body has defeated a germ some antibodies remain in the blood for some time just in case the germs try to re-invade. Even when the time of the attack is long past the body will quickly make new antibodies if it is attacked again.

The fact that the body can build up a defence to germs and make it immune from further attacks is used to make the body immune from some of the more deadly diseases. The germs carrying these diseases are killed or weakened but their antigens are left intact. The germs are then used to make vaccines. The vaccine is given by mouth or injection and body responds to the antigens by making antibodies against the disease. As the germs are harmless the person does not get the disease but the body will be ready to defend itself by producing antibodies quickly if it is ever attacked by really harmful germs in the future.