Helminthic therapy

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A larva under a microscope resembling a worm with one end across the other
Infectious Necator americanus L3 larva.
Invisible to the naked eye, from 10 to 35 are applied to the skin in therapy, either in a single dose or in multiple smaller doses over the course of two or three months.

Helminthic therapy, a type of immunotherapy, is the treatment of autoimmune diseases and immune disorders by means of deliberate infestation with a helminth or with the ova of a helminth. Helminths are parasitic worms such as hookworms and whipworms.

Helminthic therapy consists of the inoculation of the patient with specific parasitic intestinal nematodes (helminths). There are currently four such organisms used in treatment: Trichuris suis ova (TSO),[1] commonly known as pig whipworm eggs; Necator americanus,[2] commonly known as hookworms; Trichuris trichiura ova,[2] commonly referred to as human whipworm eggs; and Hymenolepis diminuta known as rat tapeworm cysticerci.

Current research and available therapy are targeted at, or available for, the treatment of Crohn's disease, ulcerative colitis, inflammatory bowel disease (IBD), multiple sclerosis, rheumatoid arthritis, polyarthritis, asthma, eczema, dermatitis, hay fever, and food allergies.

Helminthic infection has emerged as one possible explanation for the low incidence of autoimmune diseases and allergies in less developed countries, together with the significant and sustained increase in autoimmune diseases in industrialized countries.[3][4][5][6]

Incidence of autoimmune diseases and parasitic infestation[edit]

While it is recognized that there is probably a genetic disposition in certain individuals for the development of autoimmune diseases, the rate of increase in incidence of autoimmune diseases is not a result of genetic changes in humans; the rise of autoimmune related diseases in the industrialized world occurring in too short a time to be explained in this way. There is evidence that one of the primary reasons for the increase in autoimmune diseases in industrialized nations is the significant change in environmental factors over the last century. It is posited that the absence of exposure to certain parasites, bacteria, and viruses is playing a significant role in the development of autoimmune diseases in the more sanitized Western industrialized nations.[7][8] Environmental factors include exposure to certain artificial chemicals from industrial processes, medicines, farming, and food preparation.

Lack of exposure to naturally occurring pathogens and parasites may result in an increased incidence of autoimmune diseases. This is consistent with the hygiene hypothesis.[3][9] A complete explanation of how environmental factors play a role in autoimmune diseases has still not been proposed. However, epidemiological studies, such as the meta-analysis by Leonardi-Bee et al.,[3] have helped to establish the link between parasitic infestation and its protective role in autoimmune disease development.

Genetic research on the interleukin genes (IL genes) shows that helminths have been a major selective force on a subset of these human genes. In other words, helminths have shaped the evolution of at least parts of the human immune system, especially the genes responsible for Crohn's disease, ulcerative colitis, and celiac disease — and provides further evidence that it is the absence of parasites, and in particular helminths, that has likely caused a substantial portion of the increase in incidence of diseases of immune dysregulation and inflammation in industrialized countries in the last century.[10]

Hypothesis[edit]

Although the mechanism of autoimmune disease development is not fully defined, there is broad agreement that the majority of autoimmune diseases are caused by inappropriate immunological responses to innocuous antigens, driven by a branch of the immune system known as the TH1 type immune response. Extra-cellular antigens primarily trigger the TH2 response, as observed with allergies, while intracellular antigens trigger a TH1 response. The relationship between these two types of immune response is a central theme of the hygiene hypothesis, which suggests that there is a regulatory action between the two types of response. However, the observation that allergies and autoimmune response are increasing at a similar rate in industrialized nations appears to undermine the hygiene hypothesis.

The hygiene hypothesis proposes that appropriate immune response is in part learned by exposure to microorganisms and parasites, and in part regulated by their presence. In industrialized nations, humans are exposed to somewhat lower levels of these organisms. The development of vaccines, hygienic practices, and effective medical care have diminished or eliminated the prevalence and impact of many parasitic organisms, as well as bacterial and viral infections. This has been of obvious benefit with the effective eradication of many diseases that have plagued human beings. However, while many severe diseases have been eradicated, humans' exposure to benign and apparently beneficial parasites has also been reduced commensurately. The central thrust of the hypothesis is, therefore, that correct development of T regulator cells in individuals may depend on exposure to organisms such as lactobacilli, various mycobacteria, and helminths.[6] Lack of exposure to sufficient benign antigens, particularly during childhood, is sometimes suggested as a cause of the increase in autoimmune diseases and diseases for which chronic inflammation is a major component in the industrialized world.

Two refinements to the hygiene hypothesis exist, the "Old Friends" hypothesis, and the "Biome Depletion theory." [11][12]

The old friends hypothesis modifies the hygiene hypothesis by proposing that T regulator cells can only become fully effective if they are stimulated by exposure to microorganisms and parasites that have low levels of pathogenicity and that have coexisted universally with human beings throughout our evolutionary history. This hypothesis has recently been given more credibility by a study demonstrating the impact of infectious organisms, and helminths in particular, upon genes responsible for the production of various cytokines, some involved in the regulation of inflammation, in particular those associated with the development of Crohn's Disease, ulcerative colitis, and celiac disease.[10]

The Biome Depletion theory posits that the absence of an entire class of organisms from the human inner ecology (biome) is a profound evolutionary mismatch that destabilizes the immune system, resulting in disease. The biome is "depleted." The way to correct the dysregulation is to "reconstitute", or replenish, keynote species in healthy individuals prior to the development of human diseases of modern living. As keynote organisms, helminths are central to correcting immune dysregulation, and their replenishment may be a disease preventative. [13] Biome depletion theory departs from a drug model approach, which remains the current focus of helminthic therapy as evidenced by numerous clinical trails now underway for existing disease states.

Research[edit]

Helminthic therapy is currently being studied as a treatment for several (non-viral) autoimmune diseases including celiac disease,[14][15] Crohn's disease,[16][17][18][19] multiple sclerosis,[20] ulcerative colitis,[21] and atherosclerosis.[22]

Hookworms have been linked to reduced risk of developing asthma, while Ascaris lumbricoides (roundworm infection) was associated with an increased risk of asthma.[3]

See also[edit]

References[edit]

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  3. ^ a b c d Leonardi-Bee, J.; Pritchard, D.; Britton, J. (2006). "Asthma and current intestinal parasite infection: systematic review and meta-analysis". American Journal of Respiratory and Critical Care Medicine 174 (5): 514–523. doi:10.1164/rccm.200603-331OC. PMID 16778161.  edit
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  7. ^ David E. Elliott; Robert W. Summers; Joel V. Weinstock. (2005). "Helminths and the Modulation of Mucosal Inflammation". Current Opinion in Gastroenterology 21 (2): 51–58. PMID 15687885. 
  8. ^ Mohan C. (2006). "Environment versus genetics in autoimmunity: a geneticist's perspective". Lupus 15 (11): 791–793. doi:10.1177/0961203306070005. PMID 17153852. 
  9. ^ Strachan D P. (2006). "Hay fever, hygiene, and household size". BMJ. 299 (6710): 1259–1260. doi:10.1136/bmj.299.6710.1259. PMC 1838109. PMID 2513902. 
  10. ^ a b Fumagalli M, Pozzoli U, Cagliani R, et al. (June 2009). "Parasites represent a major selective force for interleukin genes and shape the genetic predisposition to autoimmune conditions". The Journal of Experimental Medicine 206 (6): 1395–408. doi:10.1084/jem.20082779. PMC 2715056. PMID 19468064. 
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  14. ^ "Experimental hookworm infection and gluten microchallenge promote tolerance in celiac disease". Retrieved 2014-10-07. 
  15. ^ "Inoculating Celiac Disease Patients With the Human Hookworm Necator Americanus: Evaluating Immunity and Gluten-Sensitivity - Full Text View - ClinicalTrials.gov". Retrieved 2009-05-22. 
  16. ^ Hunter MM, McKay DM (2004). "Review article: helminths as therapeutic agents for inflammatory bowel disease". Aliment. Pharmacol. Ther. 19 (2): 167–77. doi:10.1111/j.0269-2813.2004.01803.x. PMID 14723608. 
  17. ^ Croese J, O'neil J, Masson J, Cooke S, Melrose W, Pritchard D, Speare R. (2006). "A proof of concept study establishing Necator americanus in Crohn's patients and reservoir donors". Gut 55 (1): 136–137. doi:10.1136/gut.2005.079129. PMC 1856386. PMID 16344586. 
  18. ^ Summers RW, Elliott DE, Urban JF, Thompson R, Weinstock JV (2005). "Trichuris suis therapy in Crohn's disease". Gut 54 (1): 87–90. doi:10.1136/gut.2004.041749. PMC 1774382. PMID 15591509. 
  19. ^ Summers RW, Elliott DE, Qadir K, Urban JF, Thompson R, Weinstock JV (2003). "Trichuris suis seems to be safe and possibly effective in the treatment of inflammatory bowel disease". Am. J. Gastroenterol. 98 (9): 2034–41. doi:10.1111/j.1572-0241.2003.07660.x. PMID 14499784. 
  20. ^ Correale J, Farez M. (2007). "Association between parasite infection and immune responses in multiple sclerosis". Annals of Neurology 61 (2): 97–108. doi:10.1002/ana.21067. PMID 17230481. 
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  22. ^ Magen E, Bychkov V, Ginovker A, Kashuba E.Chronic Opisthorchis felineus infection attenuates atherosclerosis - An autopsy study.Int J Parasitol. 2013 Jun 19. pii: S0020-7519(13)00153-7. doi: