Trichuris trichiura

Trichuris trichiura, Trichocephalus trichiuris or whipworm, is a parasitic roundworm (a type of helminth) that causes trichuriasis (a type of helminthiasis which is one of the neglected tropical diseases) when it infects a human large intestine. It is commonly known as the whipworm which refers to the shape of the worm; it looks like a whip with wider "handles" at the posterior end.[1]

This article is about the worm. For the infection, see Trichuriasis.

Whipworm(s)
Scientific classification
Kingdom: Animalia
Phylum: Nematoda
Class: Enoplea
Order: Trichocephalida
Family: Trichuridae
Genus: Trichuris
Species:
T. trichiura
Binomial name
Trichuris trichiura
(Linnaeus, 1771)

Life cycle
Life cycle of Trichuris trichiura inside and outside the human body

The female T. trichiura produces 2,000–10,000 single-celled eggs per day.[2] Eggs are deposited from human feces to soil where, after two to three weeks, they become embryonated and enter the "infective" stage. These embryonated infective eggs are ingested and hatch in the human small intestine exploiting the intestinal microflora as hatching stimulus.[3] This is the location of growth and molting. The infective larvae penetrate the villi and continue to develop in the small intestine. The young worms move to the caecum and penetrate the mucosa, and there they complete development to adult worms in the large intestine. The life cycle from the time of ingestion of eggs to the development of mature worms takes approximately three months. During this time, there may be limited signs of infection in stool samples due to lack of egg production and shedding. The female T. trichiura begin to lay eggs after three months of maturity. Worms commonly live about 1 year,[4] during which time females can lay up to 20,000 eggs per day.

Trichuris trichiura is a roundworm that infects the intestines.[4] It can cause various symptoms and can lead to death. Trichuris trichiura lives in the soil in egg stage. Once it is ingested it develops into larvae stage. Finally maturing into the adult stage in the intestines.[5]

Recent studies using genome-wide scanning revealed two quantitative trait loci on chromosome 9 and chromosome 18 may be responsible for genetic predisposition or susceptibility to infection of T. trichiura by some individuals.

Morphology
Egg of Trichuris trichura

Trichuris trichiura has a narrow anterior esophageal end and shorter and thicker posterior end. These pinkish-white worms are threaded through the mucosa. They attach to the host through their slender anterior end and feed on tissue secretions instead of blood. Females are larger than males; approximately 35–50 mm long compared to 30–45 mm.[6] The females have a bluntly round posterior end compared to their male counterparts with a coiled posterior end. Their characteristic eggs are barrel-shaped and brown, and have bipolar protuberances.

Infection
Main article: Trichuriasis

Trichuriasis, also known as whipworm infection, occurs through ingestion of whipworm eggs and is more common in warmer climates. Whipworm eggs are passed in the feces of infected persons, and if an infected person defecates outdoors or if untreated human feces is used as fertilizer, eggs are deposited on soil where they can mature into an infective stage.[4] Ingestion of these eggs "can happen when hands or fingers that have contaminated dirt on them are put in the mouth or by consuming vegetables or fruits that have not been carefully cooked, washed or peeled."[4] The eggs hatch in the small intestine, then move into the wall of the small intestine and develop. On reaching adulthood, the thinner end (the anterior of the worm) burrows into the large intestine, the thicker (posterior) end projecting into the lumen, where it mates with nearby worms. The females can grow to 50 mm (2.0 in) long.[2]

Trichuris trichiura can cause the serious disease Trichuris dysentery syndrome (TDS), with chronic dysentery, anemia, rectal prolapse, and poor growth.[7] TDS is treated with anthelminthics as well as iron supplementation for anemia.[8]

Whipworm commonly infects patients also infected with Giardia, Entamoeba histolytica, Ascaris lumbricoides, and hookworms.

Treatment

Trichuris trichiura can be treated with a single dose of albendazole.[9] In Kenya, half of a group of children who had Trichuris trichiura were given albendazole, while the other half of the children received placebos. It was found that the children who received the drug grew significantly better than the group of children who did not receive the treatment. Another treatment that can be used is mebendazole. These medication have been shown to lessen the infection by this parasite through paralyzation. The medication interferes with the parasite’s nutrient intake, which eventually leads to death.

Epidemiology

There is a worldwide distribution of Trichuris trichiura, with an estimated 1 billion human infections.[10][11][12][7] However, it is chiefly tropical, especially in Asia and, to a lesser degree, in Africa and South America. Within the United States, infection is rare overall but may be common in the rural Southeast, where 2.2 million people are thought to be infected. Poor hygiene is associated with trichuriasis as well as the consumption of shaded moist soil, or food that may have been fecally contaminated. Children are especially vulnerable to infection due to their high exposure risk. Eggs are infective about 2–3 weeks after they are deposited in the soil under proper conditions of warmth and moisture, hence its tropical distribution.

A closely related species, Trichuris suis, which typically infects pigs, is capable of infecting humans. This shows that the two species have very close evolutionary traits. However, morphology and developmental stages remain different, which makes them two separate species.[13]

Treatment of inflammatory disorders
Main article: Helminthic therapy

The hygiene hypothesis suggests that various immunological disorders that have been observed in humans only within the last 100 years, such as Crohn's disease, or that have become more common during that period as hygienic practices have become more widespread, may result from a lack of exposure to parasitic worms (helminths) during childhood. The use of Trichuris suis ova (TSO, or pig whipworm eggs) by Weinstock, et al., as a therapy for treating Crohn's disease[14][15][16] and to a lesser extent ulcerative colitis[17] are two examples that support this hypothesis. There is also anecdotal evidence that treatment of inflammatory bowel disease (IBD) with TSO decreases the incidence of asthma,[18] allergy,[19] and other inflammatory disorders.[20] Some scientific evidence suggests that the course of multiple sclerosis may be very favorably altered by helminth infection;[21] TSO is being studied as a treatment for this disease.[22][23]

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References
  1. EMedicine|article|788570|Trichuris Trichiura
  2. Cross, John H. (1996). "Enteric Nematodes of Humans". In Baron, Samuel (ed.). Medical Microbiology (4th ed.). Galveston: University of Texas Medical Branch at Galveston. ISBN 978-0-9631172-1-2.
  3. Hayes, K. S.; Bancroft, A. J.; Goldrick, M.; Portsmouth, C.; Roberts, I. S.; Grencis, R. K. (2010). "Exploitation of the Intestinal Microflora by the Parasitic Nematode Trichuris muris". Science. 328 (5984): 1391–4. Bibcode:2010Sci...328.1391H. doi:10.1126/science.1187703. PMC 3428897. PMID 20538949.
  4. "CDC - Trichuriasis". 2019-04-25.
  5. Citation error. See inline comment how to fix.
  6. "Trichuris trichiura definition - Medical Dictionary definitions of popular medical terms easily defined on MedTerms". Medterms.com. 2000-04-15. Retrieved 2009-05-19.
  7. Stephenson, L.S.; Holland, C.V.; Cooper, E.S. (15 June 2001). "The public health significance of Trichuris trichiura" (PDF). Parasitology. 121 (S1): S73–S95. doi:10.1017/S0031182000006867. hdl:2262/40190. PMID 11386693.
  8. Stephenson, L.S.; Holland, C.V.; Cooper, E.S. (2000). "The public health significance of Trichuris trichiura". Parasitology. 121 (S1): S73–S95. doi:10.1017/S0031182000006867. hdl:2262/40190. PMID 11386693.
  9. Stephenson, Lani S., et al. “Treatment with a Single Dose of Albendazole Improves Growth of Kenyan Schoolchildren with Hookworm, Trichuris Trichiura, and Ascaris Lumbricoides Infections.” The American Journal of Tropical Medicine and Hygiene, The American Society of Tropical Medicine and Hygiene, 1 July 1989, www.ajtmh.org/content/journals/10.4269/ajtmh.1989.41.78.
  10. Crompton, DW (1999). "How much human helminthiasis is there in the world?". The Journal of Parasitology. 85 (3): 397–403. doi:10.2307/3285768. JSTOR 3285768. PMID 10386428.
  11. de Silva, Nilanthi R; Brooker, Simon; Hotez, Peter J; Montresor, Antonio; Engels, Dirk; Savioli, Lorenzo (2003). "Soil-transmitted helminth infections: updating the global picture". Trends in Parasitology. 19 (12): 547–51. doi:10.1016/j.pt.2003.10.002. PMID 14642761.
  12. "Trichuris trichiura". WrongDiagnosis.com. 2009-05-06. Retrieved 2009-05-19.
  13. Beer, RJ (January 1976). "The relationship between Trichuris trichiura (Linnaeus 1758) of man and Trichuris suis (Schrank 1788) of the pig". Research in Veterinary Science. 20 (1): 47–54. doi:10.1016/S0034-5288(18)33478-7. PMID 1257627.
  14. 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.
  15. 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.
  16. 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" (PDF). Am. J. Gastroenterol. 98 (9): 2034–41. CiteSeerX 10.1.1.457.8633. PMID 14499784.
  17. Buning, J; et al. (March 2008). "Helminths as governors of inflammatory bowel disease". Gut. 57 (8): 1182–1183. doi:10.1136/gut.2008.152355. PMID 18628388. in our patient Treg [regulatory T cells] activated by helminthosis [T. suis infestation] were most likely the key element protecting a host with latent ulcerative colitis against development of a severe protcocolitis. (1183)
  18. "Helminthic Therapy: How to put your Asthma, Colitis, IBD, Crohn's or Multiple Sclerosis into remission with hookworm". Asthmahookworm.com. Archived from the original on 2009-08-05. Retrieved 2009-05-19.
  19. "Allergies: Trichuris suis Ova (TSO) Therapy to Treat Food Allergies". Allergizer.com. Retrieved 2009-05-19.
  20. Bager, Peter; Kapel, Christian; Roepstorff, Allan; Thamsborg, Stig; Arnved, John; Rønborg, Steen; Kristensen, Bjarne; Poulsen, Lars K.; Wohlfahrt, Jan (2011-08-02). "Symptoms after Ingestion of Pig Whipworm Trichuris suis Eggs in a Randomized Placebo-Controlled Double-Blind Clinical Trial". PLOS ONE. 6 (8): e22346. Bibcode:2011PLoSO...622346B. doi:10.1371/journal.pone.0022346. ISSN 1932-6203. PMC 3149054. PMID 21829616.
  21. 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.
  22. "Asphelia Announces Initiation of an Independent TSO Trial for Multiple Sclerosis". redOrbit. 2008-04-07. Retrieved 2009-05-19.
  23. Klaver, Elsenoor J.; Kuijk, Loes M.; Laan, Lisa C.; Kringel, Helene; van Vliet, Sandra J.; Bouma, Gerd; Cummings, Richard D.; Kraal, Georg; van Die, Irma (2013). "Trichuris suis-induced modulation of human dendritic cell function is glycan-mediated". International Journal for Parasitology. 43 (3–4): 191–200. doi:10.1016/j.ijpara.2012.10.021. PMID 23220043.

Caroline Pomeroy, PhD July 9th, 2019.

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