A disease is any condition which results in the disorder of a structure or function in a living organism that is not due to any external injury. The study of disease is called pathology, which includes the study of cause. Disease is often construed as a medical condition associated with specific symptoms and signs. It may be caused by external factors such as pathogens or by internal dysfunctions, particularly of the immune system, such as an immunodeficiency, or by a hypersensitivity, including allergies and autoimmunity.
Before the curing of a strong disease, Even in the instant of repair and health, The fit is strongest; evils that take leave, On their departure most of all show evil.
William Shakespeare, King John (1598), Act III, scene 4, line 112.
The growth of blue-green algae in our lakes, large ponds, water reservoirs and public waters constitutes a problem for our environment and for our health. These types of algae often result in a deterioration of the water quality and emit a distinctly unpleasant odour. The algae consume a lot of oxygen in the water, leaving little for other animals like fish. They also produce toxins which can cause skin irritations and are suspected to be involved in the occurrence of liver cancer.