Two of the greatest accomplishments in human history were the formulation of germ theory (the recognition that many diseases were caused by microscopic entities (primarily bacteria and viruses)) and the development of sanitation technologies (which controlled our exposure to the potentially pathogenic bacteria and viruses around us). Stephen J. Gould, discussing the history of medicine, asserted that sanitation has saved more human lives and prevented more disease and human suffering than any other single medical invention or advance. No antibiotic or other drug, no medical therapy or surgical procedure comes close to the profound impact on human survival as sanitation.
Germ theory was first outlined in the Sixteenth Century, but it did not achieve widespread acceptance in science or medicine until Louis Pasteur and Robert Koch described and defined the science of microbiology in the mid Nineteenth Century. Even after Pasteur and Koch’s incredibly compelling experiments and papers many doctors and scientists clung to the old ideas of “bad air” (“miasma”) as the cause of disease and rejected the ideas of microscopic pathogens as delusional fantasies. The ongoing revolution in thought in the Nineteenth Century in which germ theory supplants these old ideas of disease is a fascinating story that highlights the inherent conservatism of human thought and the destructive influence of blind, collective belief in the control of our concepts of truth and reality. Two books about this time period that I highly recommend are Steven Johnson’s “The Ghost Map” and J. G. Farrell’s “The Siege of Krishnapur.” Both focus on the causes and treatments of one of the great killers of humanity (cholera), and in both the “old guard” of medicine belittle and dismiss the forces of science and innovation until the reality of the new ideas is too overwhelming to ignore.
So, germ theory (and its technological outgrowth, sanitation) are concepts that have been solidly with us for less than two hundred years. The successes of these ideas and technologies in saving lives are undeniable, but we are starting to see some points of conflict between our new “sanitary” way of living with the bacteria and viruses (and also potential protist and invertebrate parasites) around and within us and the way we have co-evolved with these organisms over the past hundreds of thousands or even millions of years.
For example, modern industrialized societies have taken the idea of sanitation to its logical extreme especially when it comes to infants and children. If exposure to potential pathogens may cause disease, then, logically, you should do anything you can to eliminate the chance of any exposure or contact with any microbe at all. Extremely clean nurseries and homes (and all of the cleaning and sanitizing products that have made this possible) were the goals of the modern, industrialized household. Isolating children from portions of the human population that might carry pathogens and restricting the exposure of children to dirt and contaminants of the surrounding world were considered to be obligations of the modern parent.
These acts, though, had profound impacts on the immune systems of the “sanitized” children. The human immune system has evolved to “expect” a series of pathogen exposures especially in early life. These pathogens allow the immune system to learn to synthesize the correct types of proteins and immune cells to form an efficient, disease fighting system for life. Research indicates that when these early life microbial exposures do not occur, the immune system develops some odd, and potentially destructive pathways that include the generation of allergies, eczema, asthma and, possibly a number of “autoimmune” disease syndromes. This is the essence of the “hygiene hypothesis.” The stunting of the immune system’s evolutionarily derived education/maturation period may at least partially explain the epidemic of allergy and asthma cases that are seen in our industrialized societies.
An intellectual continuation of the hygiene hypothesis involves the influence of parasites on the human homeostasis. A number of scientifically credible papers have been published over the past decade in which the influence of hookworm infections on the potential of an individual to resist immune disruptions were examined. For example, in the AAAS (“American Association for the Advancement of Science”) Newsletter of Feb. 20, 2011 a gene was described in a population of Brazilian school children that conveyed resistance to hookworm infections. The children that carried this gene, though, had a higher incidence of asthma than children who did not have a genetic protection against hookworm. Papers in the journal Inflammatory Bowel Diseases indicate that the presence (or introduction) of hookworms into patients with ulcerative colitis or Crohn’s disease lessens the severity of these autoimmune conditions. Further, other studies (some anecdotal and some scientific) point toward the efficacy of hookworm infections as protections against or treatments for a range of immune system disruptions including multiple sclerosis and many allergy syndromes.
An article in a recent (July 14, 2017) New York Times describes Dr. Ben Trumble’s research on the Tsimané people of Bolivia. Dr. Trumble (of Arizona State University) studies evolutionary medicine and became interested in the incidence of late-onset Alzheimer’s disease in the Tsimané. Many of the Tsimané, once they survive a very high infant mortality period, live well into their ninth decade, so Dr. Trumble was able to test a substantially large cohort for mental acuity. He also did DNA analysis to look for the ApoE4 gene (the gene referred to as the “Alzheimer’s gene” in many industrialized nation studies). He was very interested to see if there were any differences in the incidence of dementia and correlations of ApoE4 in these pre-industrial people compared to the “Western Educated Industrial Rich and Democratic” people (which he refers to as the “WEIRD’s”).
The results were very interesting. In a WEIRD population, an individual with two ApoE4 genes (about 2% of the population) develops late onset Alzheimer’s ten times more frequently than someone who lacks this gene (about 75% of the WEIRD population, by the way, lacks ApoE4). In the Tsimané, though, individuals with two or even with just one ApoE4 genes actually had higher mental acuity test scores than those individuals who lacked the gene. The “Alzheimer’s gene” of western medicine seemed to be working in different ways in the pre-industrial Tsimané. The difference, Trumble hypothesized, was parasites. The Tsimané have very high levels of parasites in their bodies (70% of Tsimané are infected with parasites at any one time!). Trumble suggests that the presence of the parasites allowed the ApoE4 gene to take on a protective role in brain homeostasis, while the absence of the parasites led to the unregulated, and potentially destructive activity of ApoE4 which possibly caused or at least accelerated the mental declines of Alzheimer’s.
Last week, I had the pleasure of talking to Dan Cummings (a PhD student from the University of New Mexico) who is a member of the Tsimane Health and Life History Project. Dan talked about not only the Alzheimer’s research mentioned above but also about some findings concerning the remarkable cardiovascular health of older Tsimané individuals. The working hypothesis in these studies is that the robust, late life health of these people is related to their life-long exposure to parasites!
Our immune systems are designed to identify and destroy foreign cells inside our body. When it works, our bodies stay free of disease and are able to maintain homeostasis. When our immune system does not work properly, though, cancers can grow out of control, powerful cells and chemicals can destroy our own tissues, and greatly exaggerated (and potentially destructive) reactions to non-dangerous substances can occur. We are just beginning to see how our immune system gets and stays “educated” and focused! Our microbiome, our surrounding microflora, and even our parasites may be important evolutionary and physiological players that enable us to keep the system functioning!