Disease

A disease is a condition in which the life of an organism does not proceed easily; Encyclopedia Britannica defines it as "a harmful deviation from the normal structural or functional state of an organism". Modern medicine recognizes many, but not all, diseases as infections by bacteria, other microbes, or viruses. A more holistic approach blames disease on stress, since germs are everywhere (like radiation and toxins). This has some factual basis, though, as stress can weaken the immune system.

The study of disease is called pathology.

Germ theory and "dis-ease"
Germ theory is the scientific theory that many diseases are caused by germs, a catchall term for pathogenic microscopic bacteria, viruses, and parasites. Many forms of alternative medicine presuppose a different cause of illness, and don't bother to verify whether those suppositions hold true.

One common trope from chiropractic and other alternative medicine proponents who happen to, ahem, "have disagreements" with germ theory is to stylize the word disease as dis-ease (with a hyphen), and hearken back to the original definition of disease ("A lack of ease; uneasiness; trouble; vexation; disquiet").

Pathogens

 * Virus
 * Bacteria
 * Fungus
 * Parasite
 * Prion