Disease is a medical term used to describe a state of the body that interferes with its normal functions and causes symptoms. A disease has a specific cause, such as an infection or genetic mutation, and is diagnosed through medical tests and physical examination. A disorder, on the other hand, may lack a clear cause and is instead identified by its impact on functioning (e.g., ADHD). A disease can be cured by addressing its underlying cause, such as antibiotics for bacterial infections or insulin for diabetes.
A disease can affect different parts of the body, depending on the underlying cause. For example, a disease of the eye can cause problems with vision or eye movement, while a disease of the skin may affect sensitivity and pain. Diseases can be infectious or non-infectious, and the latter can be caused by a variety of microorganisms, including bacteria, viruses, protozoa and fungi. Some diseases can be spread through direct contact with a person or animal carrying the disease, while others can occur in the environment as a result of contaminated water, food and air.
Diseases can also be idiopathic, meaning that their cause is unknown. The vast majority of diseases have known or suspected causes, but with some exceptions, finding the etiology of a disease is a monumental achievement requiring years of work by a single investigator. For example, Louis Pasteur’s discovery of the bacterium responsible for anthrax is an excellent case in point.