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.
physical symptoms of disease
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
Diseases may be communicable or noncommunicable. External sources that can cause disease include acquired viruses or bacteria, and internal causes of it 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 with their pain, distress or social problems. Atypical variations of structure and function, deviant behaviors, disabilities, disorders, injuries, infections and syndromes may be the signs of it or may be confused with actual disease processes.