The science and study of the causes of disease and their mode of operation. Communicable (contagious: mode of transmission: direct and indirect, bacteria, viruses, parasites, and fungi. Non-communicable (non-contagious: long duration, cardiovascular disease, cancers, diabetes. Infectious communicable: vertical transmission = individual to offspring, horizontal transmission = infected individual to susceptible individual. Susceptibility: likelihood of host developing disease, primary prevention. Pre-symptomatic: exposure begins, incubation period, latency period, secondary prevention. Clinical disease: manifestation of signs and symptoms, secondary and tertiary prevention. Recovery, disability, or death: prognosis of disease, tertiary prevention. Congenital and hereditary: familial tendencies, developmental problems. Allergies and inflammatory: reacting to an invasion of a foreign object, allergen substance that can cause an allergic reaction. Degenerative: lower level mental, physical, or moral state than normal, aging process. Metabolic: dysfunction, poor function, or malfunction of certain organs. Cancer: uncontrolled cell growth or loss of the cell"s ability to perform apoptosis.