Disease
A disease is any condition which results in the disorder of a structure or function in a living organism that is not due to any external injury. The study of disease is called pathology, which includes the study of cause. Disease is often construed as a medical condition associated with specific symptoms and signs. It may be caused by external factors such as pathogens or by internal dysfunctions, particularly of the immune system, such as an immunodeficiency, or by a hypersensitivity, including allergies and autoimmunity.
Immunology
Immunology is a branch of biology that covers the study of immune systems in all organisms. Immunology charts, measures, and contextualizes the: physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders (such as autoimmune diseases, hypersensitivities, immune deficiency, and transplant rejection); the physical, chemical and physiological characteristics of the components of the immune system in vitro, in situ, and in vivo. Immunology has applications in numerous disciplines of medicine, particularly in the fields of organ transplantation, oncology, virology, bacteriology, parasitology, psychiatry, and dermatology.
Disease
O, he's a limb, that has but a disease;
Mortal, to cut it off; to cure it, easy.
William Shakespeare, Coriolanus (c. 1607-08), Act III, scene 1, line 296.
Disease
[Diseases] crucify the soul of man, attenuate our bodies, dry them, wither them, shrivel them up like old apples, make them as so many anatomies.
Robert Burton, The Anatomy of Melancholy (1621), Part I, scene 2. Memb. 3. Subsect. 10.