Disease is the medical term for any condition that impairs or interferes with the normal function of a living organism or its parts. Diseases are usually caused by pathogenic microorganisms such as fungi, viruses, bacteria and protozoa (or occasionally by multicellular organisms such as parasites). Diseases can also be caused by aberrant proteins known as prions.
Diseases can be acute or chronic. Acute diseases are typically short-lived and can be treated, whereas chronic diseases persist for long periods of time and can often cause death. The four main types of disease are infectious diseases, deficiency diseases, hereditary diseases and physiological diseases.
What counts as a disease tends to change over time, partly for historical reasons and partly because of the ability to identify new causes and treatments. For example, osteoporosis used to be considered a normal part of getting old but it now qualifies as a disease in its own right.
A major challenge for health professionals is to define a cure. It is important to recognise that some conditions are not curable – such as certain cancers and autoimmune disorders – and to be able to explain this clearly to patients.
In the meantime, it is possible to improve a patient’s quality of life and minimize discomfort with strategies such as reducing stress, eating a well-balanced diet, exercising regularly and getting adequate rest. Emotional support from friends and family can be very useful and joining a well-facilitated support group can also be helpful.