disease

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Condition that disturbs or impairs the normal state of an organism. Diseases can occur in all living things, and normally affect the functioning of cells, tissues, organs, or systems. Diseases are usually characterized by specific symptoms and signs, and can be mild and short-lasting (such as the common cold) or severe enough to decimate a whole species (such as Dutch elm disease). Diseases can be classified as infectious or noninfectious. Infectious diseases are caused by micro-organisms, such as bacteria and viruses, invading the body; they can be spread across a species, or transmitted between one or more species. All other diseases can be grouped together as noninfectious diseases. These can have many causes: they may be inherited (congenital diseases); they may be caused by the ingestion or absorption of harmful substances, such as toxins; they can result from poor nutrition or hygiene; or they may arise from injury or ageing. The causes of some diseases are still unknown.

Some diseases occur mainly in certain climates or geographical regions of the world. These diseases are said to be endemic in the regions concerned. For example, African sleeping sickness, which is carried by the tsetse fly, is found mainly in the very hot, humid regions of Africa. Similarly, malaria, a disease spread by mosquitoes, is usually found in or near the marsh or stagnant water that provide breeding grounds for the insect. Other diseases may be seasonal – such as influenza, which tends to occur mainly in winter, or intestinal illnesses that result from food contamination in summer.

Some age groups may be more prone to certain diseases, such as measles in children, meningitis in young adults, and coronary heart disease in the elderly. Other diseases may tend to occur only in certain racial types and are usually genetic in origin, such as sickle-cell disease which is found mainly among people of black African descent. Other diseases, such as black lung, or coal-workers' pneumoconiosis, result from occupational hazards; some of the ‘new’ diseases that have appeared in recent years – such as sick building syndrome and legionnaire's disease, result from modern building designs, while the cause of ME (myalgic encephalomyelitis), or chronic fatigue syndrome, is still unknown.

Red, white, and blue recall the French tricolour. Red, yellow, and green are the pan-African colours. Red represents the common blood of mankind which links African and European nations. Effective date: 1 December 1958. >>