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Health can be defined as a person’s physical, mental and social condition. Good health is more than being free from disease; it is having a positive outlook on life and feeling good physically. To enjoy good health, a person needs proper shelter, nutrition, exercise, sleep and rest. Good hygiene and the access to medical and social care are also important.

Disease is a disorder or malfunction of the mind or body, which destroys good health.

Disease may have a single cause — for example, malaria or be multifactorial, such as heart disease. Diseases have characteristic symptoms, which may be physical, mental or both.

Those that have a sudden onset with rapid changes, but only last for a short time are called acute, while the effects of chronic disease may continue for months or years.

Categories of disease
There are nine main categories of disease but some diseases are more difficult to classify and fit into more than one of them.

Physical disease

These diseases involve temporary or permanent damage to the body and include all the other categories except mental disease where there is no sign of physical damage to the brain. An example would be leprosy.

Infectious disease

Pathogens are organisms living in or on our bodies, causing disease. Infectious diseases are caused by pathogens such as viruses, bacteria, fungi, protoctists, worms and insects, which can be transmitted from person to person. This may be via normal social contact — for example, chicken pox, or via food and water, sexual contact or an animal bite.

Carriers are people who can transmit the pathogen but do not have the disease symptoms.

Non-infectious diseases
These are all diseases, which are not caused by pathogens and cannot be passed on by physical contact. An example would be sickle cell anaemia.

Deficiency diseases

These are nutritional diseases caused by an inadequate or unbalanced diet. One or more essential nutrient is missing or in short supply — for example, a shortage of Vitamin C causes scurvy.

Inherited diseases

These diseases are caused by genes and can therefore be passed from parent to child. They are also sometimes called genetic diseases or disorders.

In Britain, the most common inherited disease is cystic fibrosis, which is characterised by a build-up of sticky mucus. This makes breathing difficult and can act as a breeding ground for bacteria, so sufferers need daily physiotherapy to remove the mucus.

It is caused by a recessive faulty allele and so parents may be carriers for the disease without having any symptoms. As yet, genetic diseases may be treated but not cured because we cannot replace the faulty gene (gene therapy).

The Human Genome Project involves scientists in many countries and began in 1990.

It aims to:

Determine the sequence of the bases throughout all the DNA in human cells.

Identify the estimated 1 000, 000 genes formed by the bases.

Find the location of the genes on the 23 human chromosomes.

Store all this information for research.

Consider the ethical, legal and social issues arising from this information.

Human Genome Project

The findings have already had a major impact, such as the devising of diagnostic tests to see if parents are carriers for a particular disease.

In the future, drugs that act against the faulty gene causing a disease may be developed, which will have fewer side effects and be more effective.

The replacement of faulty genes or gene therapy may become commonplace.

Many people are concerned about the implications of genetic testing. In many cases there may be no treatment for a disease that we can test for. There are also risks of discrimination by employers, insurance companies and others if they discover an individual has a positive test for a faulty gene.

How reliable will the test be?

How will they be made available to the world’s poorest nations?

Degenerative diseases

These diseases are characterised by a gradual loss of function, in one or several organs or tissues. In old age, this is often the result of the failure of the bodies repair mechanisms — for example, loss of mobility due to worn joints.

However, degenerative diseases can strike in ones youth or middle age. They may be the result of poor nutrition in childhood or due to the immune system attacking the bodies, own cells.

There are three main categories:

Diseases of skeletal, muscular and nervous tissues — for example, osteoarthritis.

Cardiovascular diseases of the circulatory system – for example, coronary heart disease.

Cancers.

Mental disorders

These disorders affect a person’s mind, but may be accompanied by physical symptoms. Emotions, thoughts, memories and personal and social behaviour can be affected.

Some mental diseases are caused by degeneration of brain tissue — for example, Alzheimer’s — a progressive deterioration in memory is followed by a general decline in all mental faculties (dementia).

Other mental disorders seem to be accompanied by changes in the blood flow to the brain — for example, Schizophrenia.

Social diseases

This is a very wide category that can include almost all infectious diseases and multifactorial diseases, which are influenced by people’s living conditions and their personal behaviour.

For example, deficiency diseases may be the result of lack of choice of food, due to shortage of money.

Self-inflicted diseases

These diseases are caused by damage to a person’s health by their own decisions and behaviour. Included in this category would be the choice to smoke or misusing drugs, sunbathing or eating a high fat diet.

Deliberate self-harm, such as attempted suicide, could also be placed here although it is often an indication of poor mental health.

Terms used to describe diseases

An infectious disease, which is always present in a population, is called endemic.

An epidemic occurs when a disease suddenly spreads rapidly and affects many people. If a disease spreads over a continent or even the world it will be termed pandemic. — s-cool.uk