Types of Diseases

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Congenital diseases

These are diseases that people are born with. They are often caused by faulty chromosomes. Babies suffering from Down’s syndrome, or mongolism, for example, have 47 chromosomes in their cells instead of 46. This makes them mentally handicapped.


These are the second most common cause of death in countries with a high standard of living, after heart and circulatory disease. A cancer is a disorder of cell growth. In normal tissues the cells divide and multiply only under carefully regulated conditions. A cancer cell (also called a malignant cell) is one that has undergone a change which frees it from this regulation. It divides and multiplies without control, damaging healthy cells in the process. As well as growing in one place to form a tumor (swelling), malignant cells can spread around the body and start up other tumors. (Not all tumors are cancerous. Some are fairly harmless.)

Cancers usually develop in older people though anyone may be affected. They can start in any part of the body. Some parts most commonly affected are the lungs, breasts, colon, skin, and blood (this is called leukemia).

Treatment: New discoveries are being made about cancer all the time and many people with the disease can now be cured. There are three main types of cancer treatment. Some tumors can be removed in an operation, some are damaged by radiation (radiotherapy), and some can be destroyed by very strong drugs (chemotherapy).

Degenerative diseases

These are caused by the body tissues gradually wearing out, or “degenerating,” with use and old age. Loss of sight, deafness and arthritis (inflammation of the joints) can all be degenerative diseases.

Heart and circulatory diseases

The formation of a blood clot in a blood vessel is called a thrombosis. This is one of the most common causes of a heart attack. If the thrombosis is in one of the arteries to the brain, part of the brain is deprived of blood and is damaged. This is a “stroke.” The symptoms, paralysis or loss of speech for example, depend on which area is affected.

Mental illness

There can be many reasons for mental illness. Stress from the environment is often part of the cause. Examples of mental illnesses are nervous breakdowns (often caused by depression) and anorexia nervosa (when young women develop a fear of getting fat and stop eating).

Environmental diseases

These are caused by harmful substances in the surroundings. The lung disease asbestosis, for example, is caused by asbestos dust. One of the dangerous chemicals in exhaust fumes is lead, which may interfere with the development of children’s brains. Radiation, from nuclear bomb tests, for example, may cause cancers. It can also damage chromosomes and so harm future generations.

Infectious diseases

Most of these are caused by microbes, or micro-organisms, which are living things so small they can only be seen with a microscope. Not all microbes cause disease. Many are living in or on your body all the time quite harmlessly. Some are even used to make foods such as cheese, yoghurt and bread.

viruses: These are the smallest microbes. They can only grown inside living cells. They invade your cells and use the cells’ resources to multiply. This damages the cells and produces the symptoms of disease. Many illnesses are viral. A serious one is polio; milder ones include colds, influenza (flu), measles, chicken pox, mumps, German measles, cold sores from herpes (type 1) and verrucae (a type of wart on the sole of the foot).

bacteria: These are single cell microbes, about 0.001mm long. They reproduce by dividing, sometimes very rapidly. A disease may be caused either by the harmful bacteria themselves damaging you tissues or by poisons (toxins) which they produce. Bacterial diseases include TB (tuberculosis), typhoid, pneumonia, whooping cough, tonsillitis, tetanus, boils and some kinds of food poisoning.

How infectious diseases spread?

Many infectious diseases spread through the air. An infectious person breathes, sneezes or coughs out microbes and another person breathes them in. Colds, flu and measles are spread in this way. You can also get infections from food or water. Diseases such as typhoid and food poisoning are transmitted like this. Two ways food can be infected are by people and flies. Many skin diseases, such as boils and warts, are transmitted by touch. Diseases spread in this way are called contagious diseases.

Venereal Disease (VD)

This is a group of contagious diseases which are also known as sexually transmitted diseases. In 99 cases out of 100 they are caught by having sexual intercourse with an infected person. The microbes which cause the illnesses die quickly away from the warmth and moisture of the body so you cannot catch them from toilet seats, dirty sheets or towels. Gonorrhea and syphilis (both known as clap) and herpes (type 2) are the best known venereal diseases. Most venereal diseases can usually be cured if they are treated early. AIDS is a new, rare type of disease which is often transmitted sexually. Many large hospitals have special VD clinics which give confidential advice and treatment.


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