Germ Theory

In the final chapter of his book, Plagues Upon the Earth, Kyle Harper begins with the setting of a Jules Verne sci-fi novel (The Begum’s Millions). It’s a tale of two cities. One is all about industry and mass-producing weapons of destruction. The other focuses on health, which sounds like a good thing, but stifling in its own way: “… public spaces and private habits were minutely regulated to promote healthy living… Hygiene was a public imperative and private duty.” Covid-19 has brought this view to the forefront once again, but the “City of Health” approach has been going on for a while. Verne’s utopia is now a reality in many places at least if you count crude mortality rates – we’ve exceeded Verne’s expectations.

 

As public health laws were being enacted in the mid-nineteenth century, Harper writes: “It is one of history’s ironies that the sanitary reformers based their progressive public health politics on scientific principles that were already becoming obsolete. The sanitarians were mostly committed to the miasma theory of disease. In this view, filth, pollution, putrefaction are the agents of disease.” Miasma theory was challenged by ‘contagionists’ who “believed that disease was transmitted from one infected person (or infected article, like a piece of clothing or agricultural product) to another.” This was the birth of early epidemiology and bolstered the ideas of germ theory.

 

I find it particularly interesting that germ theory became ascendant in the 1860s and 1870s, around the time that atomic theory started to gain more adherents. The Karlsruhe conference of 1860 was a landmark international chemistry conference, the highlight being Cannizzaro’s work on atomic weights. The tide was turning and chemists were starting to believe (or at least invoke) invisible particles as the basis of matter that could explain their chemical experiments. There is an uncanny parallel to germ theory; Harper writes: “Germ theory is the radical idea that disease is caused when the body is invaded by microorganisms invisible to the naked eye.”

 

The two towering figures in germ theory during this period were Louis Pasteur and Robert Koch. Pasteur’s name is well-known, thanks to the widespread process of pasteurization. Pasteur’s experiments are also invoked as the death-knell of the theory of spontaneous generation (which ironically has resurfaced in origin-of-life chemistry, my area of research). Pasteur is also honored for turning vaccination into a science. I learned from Harper’s book that Pasteur chose the word ‘vaccination’ in honor of Edward Jenner’s smallpox vaccine that came from cowpox (Latin vacca for cow).

 

While Koch is less widely known than Pasteur, he is usually credited as the father of bacteriology. His breakthrough was isolating the anthrax bacterium, thus “connecting a specific microbe to a specific disease”. He then discovered the tuberculosis bacterium, the great scourge of the time. Harper writes of Koch’s contributions: “for the first time, a scientific paradigm was born in the artificial environment we know as the laboratory.” What followed as the twentieth century was born? “The hygienics of everyday life were transformed by an active campaign to disinfect the person and the household environment.” Cleaning and disinfection involves a lot of chemistry. And we started killing bugs – vectors of disease-carrying microorganisms. We became Homo hygienicus.

 

At the end of the chapter, Harper reiterates key points he has made throughout the 500+ page book. Because we now live in a human-dominated planet, “Homo sapiens now fundamentally drives patterns of evolution across the biosphere, directly and indirectly. We favor some species intentionally (cows, chickens, pigs), others unintentionally (squirrels, pigeons). We harm some specie deliberately (cockroaches, bedbugs), others inadvertently (polar bears, black rhinos, and, well, thousands of other animals). Pathogens are a special case; we harm them intentionally but benefit them inadvertently because our own biological success is an opportunity for organisms that can exploit us as sources of energy, nutrients, and cellular machinery.”

 

We should expect more global pandemic beyond Covid-19. Microorganisms evolve and replicate, adapting to new conditions quickly. As we crowd more into urban areas, as we rely on mass-produced monocultures for food, as we change land use, as global travel resumes, as wars are fought, as climate change leads to mass migrations, pathogens will adapt. We know how germ theory works. But knowing the theory will not prevent the next pandemic.