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The microbiota and the hygiene hypothesis

Allergy is on the rise as infection has waned:

Bach 2002

Over the last half-century, the incidence of many infectious diseases has decreased dramatically (e.g. measles, tuberculosis, rheumatic fever, and hepatitis A) while that for autoimmune-related disorders has reciprocally increased (e.g. multiple sclerosis, Crohn disease, asthma, and Type I diabetes) (Bach 2002). The so-called hygiene hypothesis gained attention with the identification of an inverse relationship between family size and allergic diseases and suggested that childhood infections have a protective effect for allergy. Also termed the “old friends” hypothesis, it contends that increases in autoimmune inflammatory disorders in developed countries are partly attributable to decreasing exposure to microorganisms with which humans coevolved. (Excerpted and modified from Alcock and Schwartz 2012)

Are helminths (worms) the answer?

Research informed by the evolutionary principle of genetic-environmental mismatch has led to increased understanding of the important immunoregulatory roles played by various helminths and other members of the human microbiome (the communities of microorganisms that inhabit human skin, gut, respiratory and genitourinary tracts) For instance, the presence of intestinal helminths has been associated with decreased symptoms in multiple sclerosis. Based on surprising findings like these, prospective trials of helminthic therapy (ingestion of nematodes) are underway to treat multiple sclerosis and Crohn disease. (References can be found in Alcock and Schwartz 2012)

Writing assignment: If microbial diversity is beneficial for health, and a hygienic environment harmful, what should doctors do differently to improve the heath of their patients. Please give an example applicable for pediatrics and for adult (or even geriatric) medicine.


1)Hygiene Hypothesis

2) 99th Dahlem Conference on Infection, Inflammation and Chronic Inflammatory Disorders: Darwinian medicine and the ‘hygiene’ or ‘old friends’ hypothesis 2010. Rook G. Clinical and Experimental Immunology. 160: 70–79. (optional)

3) Missing Microbes

I will post 2 additional readings by Friday October 2.


Here is the link to the Radiolab program on hygiene and hookworm:

Radiolab hookworm story

Here is an image from the recent Yatsunenko et al. study published in Nature this year, showing the differences between adult and infant microbiomes. Malawians take a little longer time to adopt the adult pattern of microbiota, compared to a US population (a).  Infant microbiotas are significantly different from the microbiota of adults (b). CLick on the image to take you to the article.


Excellent NPR piece on microbiota diversity:


Categories: Uncategorized

Joe Alcock

Emergency Physician, Educator, Researcher, interested in the microbiome, evolution, and medicine

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