Core Concepts
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A disease is a condition that disturbs the normal structure or functioning of an organism.
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Diseases may be classified broadly as:
- Communicable / infectious → caused by pathogens and capable of transmission between hosts.
- Non-communicable → generally not transmitted from person to person; examples include diabetes, hypertension and many cancers.
- Genetic / hereditary → associated with alterations in genes or chromosomes; some are inherited, while others arise from new mutations.
- Deficiency diseases → caused by inadequate intake, absorption or utilisation of essential nutrients.
- Occupational / environmental diseases → associated with workplace exposures or environmental pollutants.
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Major disease-causing agents include:
- viruses;
- bacteria;
- fungi;
- protozoa;
- helminths and other parasites;
- abnormal genes or chromosomes;
- toxins;
- nutritional deficiencies;
- environmental pollutants.