disease, any harmful deviation from the normal structural or functional state of an organism, generally associated with certain signs and symptoms and differing in nature from physical injury. A diseased organism commonly exhibits signs or symptoms indicative of its abnormal state
There are four main types of disease: infectious diseases, deficiency diseases, hereditary diseases (including both genetic and non-genetic hereditary diseases), and physiological diseases. Diseases can also be classified in other ways, such as communicable versus non-communicable diseases.
Although there is no formal definition, common diseases are those that most frequently affect us and are often those with which we are most familiar.
And what is classified as disease is essentially down to expert consensus. While the WHO doesn’t seem to have a clear definition of disease, it does at least have a definition of health. It is defined as ‘a state of complete physical, mental and social wellbeing and not merely the absence of disease or infirmity’.31 Jul 2019
The agents that cause disease fall into five groups: viruses, bacteria, fungi, protozoa, and helminths (worms). Protozoa and worms are usually grouped together as parasites, and are the subject of the discipline of parasitology, whereas viruses, bacteria, and fungi are the subject of microbiology
Microbes (bacteria and viruses) and parasites (e.g. malaria and amoebae) Injuries (accidents) Environmental impact during an individual’s lifetime – this is also linked to personal habits mentioned as ‘lifestyle’, e.g. food and fluid intake and physical exercise.
