Historical Theories of Disease Causation, Prevention, and Cure

An imbalance of vital humors (yellow bile, black bile, phlegm, and blood), first introduced by Hippocrates (460–370 BCE) and his followers in the fourth- and third-century BCE, remained the principal theory of disease causation well into the nineteenth century. Therapeutic corrections were focused on restoring humoral equilibrium through diet or purging—the latter achieved through bloodletting, emetics, diuretics, poultices, and laxatives. Diseases were felt to be acquired by inhaling foul-smelling air, referred to as the miasma theory of disease. Alcohol- and opioid-laced patent medicines flourished as “cure-alls” for virtually every type of disease. The germ theory of disease, generally credited to the pioneering works of Louis Pasteur, Joseph Lister, and Robert Koch in the mid-1800s, reduced the understanding of disease to a simple interaction between a microorganism and host. Embraced more rapidly in Europe than America, antiseptic medical and surgical practices soon followed with a marked diminution of iatrogenic infections, as did more widespread attention to personal hygiene. Initially referred to as “non-filterable” disease-causing agents, viruses were definitively identified in the 1930s with the development of the electron microscope. Vaccines were first introduced by English physician Edward Jenner in 1796 for the prevention of smallpox, followed over ensuing decades by vaccines for a large number of other diseases—many derived from killed or attenuated viruses. In 2020, modified messenger RNA vaccines were introduced, representing a new concept in vaccine development. In 1909, the arsenic-based compound Salvarsan (arsphenamine) was introduced for the treatment of syphilis. Generally regarded as the first effective antimicrobial agent, Salvarsan was followed several decades later by sulfonamides, penicillin, and vast array of other antibiotics. Current concerns referable to infectious diseases focus on ever-increasing microbial antibiotic resistance, waning vaccine immunities, vaccine hesitancy, and environmental changes favoring the propagation and spread of disease-transmitting insect vectors.