Course 10.1Lesson 3 of 3
Most diseases have many causes. The immediate cause is what directly brings on the disease, usually a microbe. Contributory causes, such as poor food, unclean surroundings, harmful habits or inherited traits, make it easier for the disease to take hold. Diseases are infectious when microbes spread them, and non-infectious when they have internal causes.
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If ten people breathe in the same cold virus, not all of them fall ill. Some get a cold and some do not. So the virus alone does not decide who becomes ill. A disease usually has more than one cause.
Doctors sort the causes into two kinds: the immediate cause and the contributory causes.
The immediate cause is the one that directly brings on the disease. In most cases it is a microbe: a virus, a bacterium, a fungus, a protozoan or a worm.
Sometimes the immediate cause is not a microbe but a harmful substance or a force. A poison in the food, for example, or a hard blow to a bone. Later in this chapter you will read how microbes spread and how they are treated.
A person who has the microbe in the body does not always fall ill. Other things decide how easily the microbe can start the disease. These are the contributory causes.
The picture shows the immediate cause and the contributory causes around one person.
Take tuberculosis. The bacterium is the immediate cause. But a person is far more likely to fall ill with TB if the food is poor and the home is crowded. Both are contributory causes.
Back to the ten people who breathed in the cold virus. The ones with enough food, rest and clean surroundings may fight it off. The ones with poor food and crowded homes are more likely to get the cold. The microbe is the same, but the contributory causes are not.
The simulation shows this idea with an invented model. The numbers are made up. The point is that more bad contributory causes mean more people fall ill, although the microbe is the same.
Diseases can also be sorted by whether they spread.
A broken bone is not a disease at all. It is an injury, and no microbe causes it. It is an example of a health problem that cannot spread to another person.
Even in non-infectious diseases there can be several causes. Cancer can come from changes inside cells, from inherited traits, and from outside causes such as tobacco smoke. A person with high blood pressure may have inherited it, or may have a poor diet and little exercise.
An infectious disease can also lead to other problems. A person who is often ill with infections becomes weak, and the weakness itself becomes a contributory cause of another disease.
A healthy body is one whose needs are met, and whose surroundings do not overload it. When the food is good, the water is clean and there is rest, the body stays in balance. When the balance is lost, because of microbes, poor food or unclean surroundings, a disease can take hold. This is why curing a disease is not enough. We must also correct the contributory causes, so that it does not return.
The program sorts five causes into immediate and contributory causes, and counts each kind.
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