A disease is an abnormal condition of an organism that impairs bodily functions and can be deadly. It is also defined as a way of the body harming itself in an abnormal way, associated with specific symptoms and signs.

In human beings,"disease" is often used more broadly to refer to any condition that causes extreme pain, dysfunction, distress, social problems, and/or death to the person afflicted, or similar problems for those in contact with the person. In this broader sense, it sometimes includes injuries, disabilities, disorders, syndromes, infections, isolated symptoms, deviant behaviors, and atypical variations of structure and function, while in other contexts and for other purposes these may be considered distinguishable categories.Fact: date=November 2007

Transmission of disease

Main: Transmission (medicine) Some diseases such as influenza are contagious and infectious. Infectious diseases can be transmitted by as, by hand to mouth contact with infectious material on surfaces, by bites of insects or other carriers of the disease, and from contaminated water or food (often via faecal contamination), etc. In addition, there are sexually transmitted diseases. In some cases, micro-organisms that are not readily spread from person to person play a role, while other diseases can be prevented or ameliorated with appropriate nutrition or other lifestyle changes. Some diseases such as cancer, heart disease and mental disorders are, in most cases, not considered to be caused by infection (see Non infectious disease), although there are important exceptions. Many diseases (including some cancers, heart disease and mental disorders) have a partially or completely genetic basis (see Genetic disorder) and may thus be transmitted from one generation to another.

Social significance of disease

Living with disease can be very difficult. The identification of a condition as a disease, rather than as simply a variation of human structure or function, can have significant social or economic implications. The controversial recognitions as diseases of post-traumatic stress disorder, also known as "Soldier's heart," "shell shock," and "combat fatigue;" repetitive motion injury or repetitive stress injury (RSI); and Gulf War syndrome has had a number of positive and negative effects on the financial and other responsibilities of governments, corporations and institutions towards individuals, as well as on the individuals themselves. The social implication of viewing aging as a disease could be profound, though this classification is not yet widespread.

A condition may be considered to be a disease in some cultures or eras but not in others. Oppositional-defiant disorderFact: date=October 2007, attention-deficit hyperactivity disorderFact: date=October 2007, and, increasingly, obesityFact: date=October 2007, are conditions considered to be diseases in the United States and Canada today, but were not so-considered decades ago and are not so-considered in some other countries . Lepers were a group of afflicted individuals who were historically shunned and the term "leper" still evokes social stigma. Fear of disease can still be a widespread social phenomena, though not all diseases evoke extreme social stigma.