Susan Sontag in NYRB (February 23, 1978):
Punitive notions of disease have a long history, and such notions are particularly active with cancer. There is the “fight” or “crusade” against cancer; cancer is the “killer” disease; people who have cancer are “cancer victims.” Ostensibly, the illness is the culprit. But it is also the cancer patient who is made culpable. Widely believed psychological theories of disease assign to the ill the ultimate responsibility both for falling ill and for getting well. And conventions of treating cancer as no mere disease but a demonic enemy make cancer not just a lethal disease but a shameful one. Leprosy in its heyday aroused a similarly disproportionate sense of horror. In the Middle Ages the leper was a social text in which corruption was made visible; an exemplum, an emblem of decay. Nothing is more punitive than to give a disease a meaning—that meaning being invariably a moralistic one. Any important disease, whose physical etiology is not understood, and for which treatment is ineffectual, tends to be awash in significance. First, the subjects of deepest dread (corruption, decay, pollution, anomie, weakness) are identified with the disease. The disease itself becomes a metaphor. Then, in the name of the disease (that is, using it as a metaphor), that horror is imposed on other things. The disease becomes adjectival. Something is said to be disease-like, meaning that it is disgusting or ugly. In French, a crumbling stone façade is still “lépreuse.”
Epidemic diseases were a common figure for social disorder. From pestilence (bubonic plague) came “pestilent,” whose figurative meaning, according to the Oxford English Dictionary, is “injurious to religion, morals, or public peace—1513”; and “pestilential,” meaning “morally baneful or pernicious—1531.” Feelings about evil are projected onto a disease. And the disease (so enriched with meanings) is projected onto the world. In the past, such grandiloquent fantasies were regularly attached to the epidemic diseases, diseases that were a collective calamity. In the past two centuries, the diseases most often used as metaphors for evil were syphilis, tuberculosis, and cancer—all diseases imagined to be, preeminently, the diseases of individuals.
Syphilis was thought to be not only a horrible disease but a demeaning, vulgar one. Antidemocrats used it to evoke the desecrations of an egalitarian age.
More here. (NOTE: Thanks to Rima Zaheer from New Delhi)