How do we know that microbes cause disease? In the middle of the nineteenth century Louis Pasteur discovered that microbes in the air make food go bad. Pasteur suggested that microbes might also cause diseases. Some years later a German doctor called Robert Koch showed that certain bacteria cause diseases such as cholera and tuberculosis. Other scientists carried out similar investigations, and by the end of the nineteenth century the particular microbes responsible for many diseases were known.
Which microbes cause diseases? Most human diseases are caused by bacteria and viruses. However, diseases also caused by certain types of fungi, protoctists and parasitic Organisms which cause diseases are called pathogens. When you get a disease, certain signs usually enable the doctor to td it is. The signs are called symptoms and they allow the doctor to a diagnosis. What do germs do to us? Germs get into the body through the nose and mouth, and through cut wounds. Once inside, they may multiply very quickly. This early stage is the incubation period, and several days or even weeks may go by before person starts feeling ill.
Germs harm us in two ways. Some of them attack and destroy our cells. Others release toxins which get into the blood. For example, the bacteria which cause cholera never leave their victim nor do they invade the cells lining it. The harm they do is caused entirely poisons which they give off. Germs may be passed from person to person In 1918 there was an outbreak of flu in Spain. Within a few months spread all over the world. Worldwide, over 20 million people died of it. Germs may stick to dust particles and float through the air. Eventually they settle on surfaces which may be a long way from where they came from. Diphtheria and tuberculosis can be spread this way. People catch the disease breathing in the dust, or getting it in their mouths from contaminated food. 3. By touch Impetigo is a skin disease that breaks out in schools sometimes. You catch it by touching an infected person.
Another skin disease is athlete’s foot. This can be picked up from the floor of changing rooms and showers. Diseases that are spread by touch are bribed as contagious.4. By faeces The faeces of a person with a disease may be swarming with germs. If the germs get into food or drinking water, the disease will quickly spread to other people. This is why it is important to wash your hands after going to the toilet.
Epidemics of typhoid, cholera and dysentery have been caused this way. Drinking water may become contaminated if sewage is not got rid of properly. This sometimes happens in poor countries. 5. By animals Germs can be brought onto food by animals such as rats and mice, cockroaches and flies. Take flies, for example. These little animals are equally happy. For example, flies love to feed on dung so their proboscis may get covered in dung.
Many diseases are spread by animals which suck blood. An example is the mosquito which transmits malaria and yellow fever. Subonic plague, the Black Death of the Middle Ages, is caused by bacteria. A vector is an animal that transmits a disease from one animal to another. A dog may carry germs on it’s tounge and then lick your face. This is why it is not a good idea to let animals lick you, and wash your hands after handling then. 6. By blood Diseases can be spread by blood. For example, sharing an injection needle when taking injection drugs is not a good idea because blood can be transmitted from one person to another. Two diseases which are known to be spread by blood are viral hepatitis and AIDS. In the past, AIDS has been spread by people being given contaminated blood in a transfusion. Nowadays blood that is to be used in a transfusion is tested beforehand.