Early Bird Gets the Worm… But Does It Want that Worm? – How Your Gut Deals with Intestinal Parasites

Adam Hassan, BSc Microbiology and Immunology
Contributor​

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Image source: http://www.return2health.net/articles/intestinal-parasites/

     Neglected tropical diseases (NTDs) refer to tropical diseases which affect low-income countries primarily in Africa, Asia, the Middle East and South America. These diseases are thought of as “neglected” due to them receiving less financial support in terms of research funding and treatment. Everyone has heard of HIV/AIDS, malaria, and tuberculosis. However, how many of you know about schistosomiasis, chikungunya fever or leishmaniasis? Causative agents of this group of diseases include viruses, bacteria or parasites (protozoa and helminths).

     Of course, most of the money and resources are in developed regions (i.e. North America and Europe). Thus, there is less incentive to invest in the treatment and prevention of NTDs if the “home” population is not directly or primarily affected. When it comes to viruses and bacteria, a lot of progress has been made. However, there are still no vaccines available for parasitic infections. You may want to remember that the next time you travel! (Disclaimer: many NTDs are treatable and it is very important to visit your travel clinic.)

     So, how do parasites affect our gut..? Well, there are several intestinal parasitic infections such as giardiasis, ascariasis, and strongyloidiasis. These parasites, often worms in the adult stage, infect your gastro-intestinal tract by the ingestion of infected food or water, the fecal-oral route, or by skin absorption. The main populations affected are actually children with the World Health Organization (WHO) estimating that number to be around 880 million (1). It is important to note that a parasite’s first instinct is not to kill you. A parasite wants to live with you as it needs you for nutrients (hence why it is called a “parasite”). Complications from how our bodies react to this unwelcomed squatter often lead to severe symptoms down the road and eventually death if left untreated for many years. 

     We have covered at great lengths in previous blog posts how complex our gut microbiota is and how the notion of balance is very important. Well, most of us would say that the presence of worms in your intestine does not quite qualify as “normal”. When parasites enter your system and mature, they interact with your gut microbiota. Often, the host’s resident gut microbiota is able to interfere with the parasite and undermine it (2). In fact, the bacteria are there to line your gut and to prevent any other microorganisms from invading and establishing itself. But behold, the parasite can also create a more favourable environment for itself. Many protozoans and helminths can secrete molecules that will affect the state of balance in our guts so that they can establish themselves within us. On top of that, parasites live with their host and profit from the nutrients that are being degraded in the intestine as well (2).

     The interactions between our gut bacteria and invading parasites are quite complex. Mouse models have shown that the same, normal gut microbiota can protect against some parasites such as Cryptosporidum but cause you to also be susceptible to other species (3,4). Interestingly, probiotics have been found to be effective against several species of parasites. So, on top of helping with gastrointestinal disorders, they play a role in stopping the development of these organisms (5). Something to remember the next time you’re eating your yogurt!  

     Finally, this leads us to the idea of modulating/altering your gut microbiota. Homeostasis is a key concept. If a parasitic organism disturbs this balance, you can restore it by introducing probiotics as mentioned above. Some species of probiotics include Lactobacilli and Bifidobacteria species. Administration of probiotics leads to a boost in the immune system. This can be observed by a growing number of immune cells (such as T cells) and IgA antibodies, which will act against the invading pathogen (6). Not only is it possible to stop the development of pathogens, it is also possible to help in your recovery if infected! 

References

1. “Intestinal Worms.” World Health Organization, World Health Organization, www.who.int/intestinal_worms/more/en/.
2. Berrilli, Federica, et al. “Interactions between Parasites and Microbial Communities in the Human Gut.” Frontiers in Cellular and Infection Microbiology, Frontiers Media S.A., 16 Nov. 2012.
3. Harp, J A, et al. “Resistance of Severe Combined Immunodeficient Mice to Infection with Cryptosporidium Parvum: the Importance of Intestinal Microflora.” Infection and Immunity., U.S. National Library of Medicine, Sept. 1992.
4. Owen, D. “Eimeria Falciformis (Eimer, 1870) in Specific Pathogen Free and Gnotobiotic Mice.” Parasitology., U.S. National Library of Medicine, Oct. 1975.
5. Travers, M A, et al. “Probiotics for the Control of Parasites: an Overview.” Journal of Parasitology Research., U.S. National Library of Medicine, Sept. 2011.
6. Vitetta, Luis, et al. “Modulating the Gut Micro-Environment in the Treatment of Intestinal Parasites.” Journal of Clinical Medicine, MDPI, Nov. 2016.