A pediatrician heard a radio story on the news about using worms to try to treat Crohn’s disease. She also was reading a book at the time where blood letting through cuts in the skin or leeches was a common medical treatment. She thought it was a good time for a quick review of organisms used for medical therapies that usually were thought of as potentially harmful creepy crawlies.
Humans are only one species among the multitudes that inhabit the earth. While many species are used by humans for food, clothing or shelter, as a higher evolved organism, humans are particularly aware of other species that move as they could be a potential predator or cause injury. This wariness is protective, but moving animal species can be domesticated (e.g. dogs, horses), farmed (e.g. cattle, goats) or harvested (e.g. fish, silk) for human use for food, clothing or shelter and also for medicinal use.
Medical leeches have been used since ancient times. The most commonly used leech is Hirudo medicinalis named by Linneaus in 1758. It attaches to the host with a posterior sucker, bites with 3 jaws, and feeds on ~2-20 ml of blood usually within 10-30 minutes. Its saliva has several anticoagulants which allows for continued blood oozing up to 48 hours. It is the oozing effect that is the most useful to help in the treatment of large soft tissue hematomas (e.g. tongue), and especially for venous congestion after surgery for tissue flap reconstructions or reimplantation after amputations. Venous congestion can cause many problems in various surgical repairs and is a common reason for tissue flap failures. Hirudotherapy (or use of medical leeches) is considered an adjuvant after determining that there is not an arterial problem or venous congestion problem that is amenable to further surgery. Hirudotherapy can also be used if additional surgery is contraindicated. Medical leeches are grown specially for medical use. After feeding they are sacrificed in 70% alcohol and disposed of as a biohazard. As the gut of the leech is directly exposed to the patient, prophylactic antibiotics are usually given. The most common leech intestinal flora organism is Aeromonas hydrophilia. The various bioactive anticoagulants in leeches’ saliva and its body are also being researched. While there are several agents, 2 of the more common ones being evaluated are hirudins and hyaluronidase. Hirudins are being invested for antithrombotic effects in venous thrombosis and acute coronary syndromes. Hyaluronidase is being evaluated to increase permeability to improve absorption of fluids.
Helminths or parasite worms are common parasites which in the past affected almost all people. Today they still affect an estimated 2 billion people globally. Helminths appear to have an immunomodulating effect on the human immune system. It is thought that because of helminthic infestations, the human immune system is actively suppressed to allow continued viability of both organisms. Unfortunately, the human host is also less reactive to some other infectious agents such as tuberculosis or malaria and hosts have decreased vaccine responses. The potential advantage for the human host is to be less responsive which can help effects of immune-mediated diseases such as atopy, rheumatoid arthritis, Crohn’s disease, etc.. Pig whipworm, Trichuris suis is one of the most common medically used helminths. There are currently ongoing clinical trials for allergies, inflammatory bowel disease, rheumatoid arthritis and multiple sclerosis using helminth-modulated macrophage therapy. Experimental laboratory therapy is also ongoing for diabetes and sepsis. With helminth therapy it is important to note that there is a balance in trying to regulate an individual’s immune system. As one author said: “Because parasitism is on balance detrimental, administration of live helminths is itself a balancing act, attempting to maximize any beneficial effects against a deleterious backdrop. Where the fulcrum of that balance sits will very much vary according to the genetic makeup of the individual.”
While leeches and helminths are creepy crawlies that can be seen, newer research is looking at a much smaller scale. A microbiome are microorganisms that can be commensal, symbiotic or pathogenic and which inhabit our body spaces during health and disease. Common places to have microbiomes are the mouth, gut, vagina, lung and skin. There are many factors which affect an individual’s microbiome including genetics, antibiotics, diet, and environmental exposure (e.g. family, pets, soil, etc.). Studies are providing more information about how the microbiome in prenatal and early life can affect potential disease especially immune-related diseases such as allergies and asthma, inflammatory bowel disease, and also weight gain and obesity and infections. As the science associated with microbiomes is relatively new yet may potentially provide important understanding of normal and disease states, the National Institute of Health has undertaken the Human Microbiome Project as one of several international large scale scientific efforts to better understand human microbiomes.
Questions for Further Discussion
1. What other examples of medical uses of potential harmful species can you think of?
2. What potential side effects do some of these species have?
To Learn More
To view pediatric review articles on this topic from the past year check PubMed.
To view current news articles on this topic check Google News.
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Porshinsky BS, Saha S, Grossman MD, Beery I PR, Stawicki SP. Clinical uses of the medicinal leech: a practical review. J Postgrad Med. 2011 Jan-Mar;57(1):65-71.
Zaidi SM, Jameel SS, Zaman F, Jilani S, Sultana A, Khan SA. A systematic overview of the medicinal importance of sanguivorous leeches. Altern Med Rev. 2011 Mar;16(1):59-65.
O’Dempsey T. Leeches–the good, the bad and the wiggly. Paediatr Int Child Health. 2012 Nov;32 Suppl 2:S16-20.
Maizels RM. Parasitic helminth infections and the control of human allergic and autoimmune disorders. Clin Microbiol Infect. 2016 Jun;22(6):481-6.
Steinfelder S, O’Regan NL, Hartmann S. Diplomatic Assistance: Can Helminth-Modulated Macrophages Act as Treatment for Inflammatory Disease? PLoS Pathog. 2016 Apr 21;12(4):e1005480.
Tamburini S, Shen N, Wu HC, Clemente JC. The microbiome in early life: implications for health outcomes. Nat Med. 2016 Jul 7;22(7):713-22.
National Institutes of Health. Human Microbiome Project Overview. Available from the Internet at http://commonfund.nih.gov/hmp/overview (rev. 5/16/16, cited 7/19/16).
Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa Children’s Hospital