A disease is an abnormal condition
that affects the body of an organism. It is often construed as a medical
condition associated with specific symptoms and signs. It may be caused by factors originally from an
external source, such as infectious disease, or it may be caused by internal
dysfunctions, such as autoimmune diseases. In humans, "disease" is
often used more broadly to refer to any condition that causes pain,
dysfunction, distress, social problems, 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. Diseases usually affect people not only
physically, but also emotionally, as contracting and living with many diseases
can alter one's perspective on life, and their personality.
Death due to disease is called death
by natural causes. There are four main types of disease: pathogenic disease,
deficiency disease, hereditary disease, and physiological disease. Diseases can
also be classified as communicable and non-communicable disease.
Resources:
http://en.wikipedia.org/wiki/Diseases