The human body's "good parasites"

Dr. Copeland By Dr. Copeland, 21st Dec 2010 | Follow this author | RSS Feed | Short URL
Posted in Wikinut>Health>General Health>Wellness

The mutualistic microbiome: a population of organisms living inside us can be beneficial to our health

Parasite, commensals, and mutualists

So-called "good parasites" in the human body have been linked to protection against a number of disease conditions, from colon cancer to obesity (1, 2). In addition, they perform general beneficial functions, such as synthesizing vitamins and helping to protect against infection from pathogenic microorganisms. In truth, however, these organisms living inside us are not, by definition, parasites. Symbionts, or organisms that live inside us or on us, can be divided into three types: parasites, which cause us harm, mutualists, which help us or do us good, and commensals, which do not necessarily do us good, but which do not hurt us. The "good parasites" are the mutualists.

Intestinal mutualists

One of the most important categories of mutualists is that of the intestinal bacteria. According to Dr. Elisabeth Bik of the Stanford University School of Medicine (3), the colon is colonized by more than a trillion organisms per gram of intestinal contents; the number of bacterial cells inside us is actually higher than the number of our own cells! These include the familiar E. coli, a natural gut-inhabiting bacterium, as well as bacteria commonly ingested in probiotic foods, such as Lactobacillus from yogurt. The vast majority of the bacteria fall within four phyla (major groups) of bacteria: Firmicutes (including Lactobacillus), Bacteroidetes, Actinobacteria, and Proteobacteria (including the familiar E. coli) (3). Methanobrevibacter smithii, an archaean (a microorganism that looks like a bacterium but which has a completely different ancestry), is another major intestinal resident in humans (4). Minority gut residents include the Fusobacteria, Cyanobacteria, Spirochaetes, and Verrucomicrobia.

Symbionts and the immune system

In addition to the clearly beneficial effects of these intestinal bacteria, there may also, paradoxically, be benefits to infection with disease organisms. Illustrating the axiom "what does not kill me makes me stronger", immunologists are increasingly finding that infection with organisms that are generally thought of as parasites can aid in the healthy development of the immune system. The prevention of infection with helminth parasites (worms) and other infectious organisms in developed countries has been linked to increased rates of allergy and asthma, and this is thought to be related to abnormal immune system development (5). It seems that such infections are actually required to correctly "wire" the immune system, and that without them, the immune system instead attacks benign substances such as pollen, resulting in allergic reactions. Infectious organisms that have been shown to provide protection against allergy include the nematode (roundworm) parasites Heligmosomoides polygyrus, Nippostrongylus brasiliensis, and species of Ascaris; the platyhelminth (flatworm) parasites Schistosoma mansoni and Schistosoma japonicum, bacteria such as Mycobacterium, Chlamydia, and Listeria, viruses, including Influenza virus and Respiratory syncytial virus, and even fungal pathogens, such as Aspergillus fumigatus (5).

It is becoming evident that the microbiome, the population of organisms that live inside us, is an important part of who we are, playing roles in gastrointestinal function, immunity, and other aspects of human health. Future molecular and genomic studies should lead to the further discovery of as-yet unknown mutualistic organisms.

References and further reading:

1. Tsai F, Coyle WJ. (2009)The microbiome and obesity: is obesity linked to our gut flora? Current Gastroenterology Reports: 11(4):307-13.

2. Kinross JM, von Roon AC, Holmes E, Darzi A, Nicholson JK. (2008) The human gut microbiome: implications for future health care. Current Gastroenterology Reports: 10(4):396-403.

3. Bik EM. (2009) Composition and function of the human-associated microbiota. Nutrition Reviews: 67:S164–S171.

4. Ley RE, Peterson DA, Gordon JI. (2006) Ecological and Evolutionary Forces Shaping Microbial Diversity in the Human Intestine. Cell: 124(4):837-848.

5. Roumier T, Capron M, Dombrowicz D, Faveeuw C. (2008) Pathogen induced regulatory cell populations preventing allergy through the Th1/Th2 paradigm point of view. Immunologic Research: 40(1):1-17.


Allergy, Asthma, Bacteria, Commensal, Immune System, Immune System Boosting, Immune Sytem, Immunity, Infection, Intestinal Parasites, Intestine, Intestines, Microbiome, Mutualist, Parasite, Parasites, Parasitic, Probiotic, Symbiotic

Meet the author

author avatar Dr. Copeland
Dr. Copeland holds a Ph.D. in molecular and cellular biology from Tulane University, specializing in tropical medicine, parasite genetics, and retrotransposons/retroviruses, with postdoctoral research experience in molecular entomology and computatio...(more)

Share this page

moderator Mark Gordon Brown moderated this page.
If you have any complaints about this content, please let us know


author avatar D in The Darling
23rd Dec 2010 (#)

Beautiful article my friend. it's one of those I call a rare share!
Keep up the good work and thanks for sharing!

Reply to this comment

author avatar NZOPUTAM
8th May 2012 (#)

plz, are there worms in the human body which are of very good benefit to human life? in digestion and other metabolic role. please, help me out. Thank you.

Reply to this comment

author avatar Dr joan saintz
24th Jul 2012 (#)

most of the "news" regarding parasites is another excuse to "drug" a healthy diet is rarely sought as a "remedy" because most will not accept responsibility for their own actions.

Reply to this comment

author avatar Dr joan saintz
24th Jul 2012 (#)

with so much information against the concept of "good" parasites this is refreshing!

Reply to this comment

Add a comment
Can't login?