3.5.1: Germ Theory

Although microorganisms had been proposed as a potential cause of disease since the 1500s, it wasn’t until better microscopes were developed in the early 19th century that germ theory became a strong rival and eventually replaced the prevailing miasma theory of disease. The work of two rival microbiologists finally solidified germ theory: Louis Pasteur’s experiments in France and Robert Koch’s in Germany. Pasteur discovered microorganisms which were affecting the silk industry, then in wine, beer, and milk. He also came up with the concept of killing or deactivating these microorganisms by heating the liquid; a technique which is named after him - called pasteurization. Pasteur was involved in studying anthrax (a bacteria) and creating vaccines for both animals and humans for a variety of infectious diseases. One of his greatest achievements was developing a vaccine for rabies, which at that time was a death sentence. Koch also researched anthrax and developed a vaccine for it, discovered the microorganisms responsible for tuberculosis and cholera, and created guidelines for establishing a specific pathogen as a causative agent of a disease - called “Koch’s postulates” (Tulchinsky & Varavikova, 2014).

Perhaps one of his greatest feats, Robert Koch discovered the bacteria that causes Tuberculosis (TB), which at the time killed 1 in 7 people in the U.S. and Europe. “Consumption” as it was often called, was a deadly infectious disease that could be spread between people via breathing and coughing, and for which the only known treatment was “warmth, rest, and good food”. In the 19th century, sanatoriums were established to isolate infected individuals, and prevent the disease from spreading to family members. The first attempt to combat TB was with a vaccine: the Bacille Calmette-Guérin (BCG) vaccine was developed in 1923, yet it was not entirely effective at preventing TB infections. Finally, several antibiotics were discovered in the 1950’s and 60’s that became an effective treatment cocktail. Tuberculosis cases in the U.S. decreased substantially over the 21st century, but even though it may seem like an “old timey” disease it has not been eliminated yet. Standardized testing, tracking, and treatment of TB cases are the current protocol until a more effective vaccine is developed (CDCTB, 2023b). Worldwide, TB is still the second leading cause of death from an infectious disease, and is the leading cause of death for people with HIV/AIDS. It can also become resistant to the 2 most effective drugs, particularly if they are improperly prescribed or the patient quits taking them too early. Newer treatments and expanded access to testing and treatments are part of the WHO priorities to work toward eliminating TB (World Health Organization, 2023).