What are diseases?

A disease is an abnormal condition affecting a living organism. Diseases are generally understood to be medical conditions that involve a pathological process associated with a specific set of symptoms. Localized diseases affect specific parts of the body; disseminated diseases spread to other parts of the body; and systemic diseases affect the entire body.

Each disease process has an origin, or etiology, but some diseases may present with different or confusing symptoms, making them difficult to diagnose or determine. The physical symptoms of disease may be accompanied by emotional symptoms, and some diseases that affect the chemical balances of the nervous system may manifest in physical symptoms.

Categories of diseases include autoimmune, bacterial, blood, cancer, digestive, heart, nerve (or neurodegenerative), sexually transmitted or thyroid. Diseases may be communicable or noncommunicable. External sources that can cause disease include acquired viruses or bacteria, and internal causes of disease include autoimmune or genetic dysfunction. Some diseases are chronic, meaning that they are continually present and may present symptomatically during a long duration.

Humans generally associate disease with pain, distress or social problems. Atypical variations of structure and function, deviant behaviors, disabilities, disorders, injuries, infections and syndromes may be the signs of disease or may be confused with actual disease processes.

Disease may be prevented or avoided using a number of strategies, including proper sanitation, proper nutrition, frequent exercise and vaccination. Treatments for disease range from medication and medical devices to surgery to self-care. Diseases may be cured simply by time, whereas others require a set of treatments that reverse the disease processes or end the root medical problem permanently. Some diseases may not be cured, in which case the symptoms of the disease may be treated using pain management therapy or palliative care.

Additional information about diseases may be found at these websites:

http://www.cdc.gov/DiseasesConditions/

http://www.mayoclinic.com/health/diseasesIndex/diseasesIndex

http://www.hhs.gov/diseases/index.html