HumBio 153: Parasites and Pestilence
D. Scott Smith
ParaSite Project: version for Carlos Seligo
Trichuriasis: Trichuris trichiura
Trichuriasis is a parasitic infection primarily in the tissue of the cecum, appendix, colon and rectum that is caused by an intestinal nematode (roundworm) called Trichuris trichiura.
Agent (classification and taxonomy)
The phylum of Trichuris trichiura is Aschelminthes, while its class is Adenophorea, its order is Stichosmida, and its family is Trichocephaloidea. Its genus, Trichocephalus, was recorded as a more accurate name, however the generic name trichuris, which means “hair tail” (which implies that the posterior end of the worm is the attenuated section), remains the dominant name form used today.
Human Whipworm, Trichocephaliasis, and Tricuriasis are all synonyms for Trichuriasis, human infection of the Trichuris trichiura intestinal nematode. In Spanish, trichuriasis is called “Tricuriasis,” while in it is known as “Trichuriose” in French and “Peitschenwurmbefall” in German.
History of Discovery
The first written record of Trichuris trichiura was made by Morgani, an Italian scientist, who identified the presence of the parasite in a case of worms residing in the colon in 1740. Exact Morphological description and figures were first recorded in 1761 by Roedere, a German physicist. Soon after morphology and visual representation of the worms, Trichuris trichiura was given taxonomy (during the 18th century).
Clinical Presentation in Humans
Light infections of Trichuris trichiura are frequently asymptomatic. Heavier infections, especially in small children, can present gastrointestinal problems including abdominal pain and distention, bloody or mucous-filled diarrhea, and tenesmus (feeling of incomplete defecation, generally accompanied by involuntary straining), which is brought upon by the weakening of the GI tract muscle tissue. While damage may be done to the GI tissue and appendicitis may be brought on (by damage and edema of the adjacent lumen) by the parasitic infection alone, if there are large numbers of worms or larvae present, it has been suggested that the embedding of the worms into the ileo-cecal region may also make the host susceptible to bacterial infection. Growth retardation, weight loss, nutritional deficiencies, eosinophilia, and anemia are also characteristic of infection, and these symptoms are more prevalent in children. Infection may also present with rectal prolapse, although this is typically seen only in heavy infections of small children. High numbers of embedded worms in the rectum cause edema, which combined with the weakened GI muscle tissue causes the rectal prolapse. The prolapsed, inflamed and edematous rectal tissue may even show visible worms.
Coinfection of Trichuris trichiura with other parasites is common and with larger worm burdens can cause both exacerbation of dangerous trichuriasis symptoms such as massive gastrointestinal bleeding (shown to be especially dramatic with coinfection with Salmonella typhi) and exacerbation of symptoms and pathogenesis of the other parasitic infection (as is typical with coinfection with Schistosoma mansoni, in which higher worm burden and liver egg burden is common). Parasitic coinfection with HIV/AIDS, tuberculosis, and malaria is also common, especially in Sub-saharan Africa, and helminth codinfection adversely affects the natural history and progression of HIV/AIDS, tuberculosis, and malaria and can increase clinical malaria severity. In a study performed in Senegal, infections of soil-transmitted helminths like Trichuris trichiura (as well as schistosome infections independently) showed enhanced risk and increased incidence of malaria.
Humans can become infected with the parasite due to ingestion of infective eggs by mouth contact with hands or food contaminated with egg-carrying soil. However, there have also been rare reported cases of transmission of Trichuris trichiura by sexual contact.
Humans are the only known reservoir for Trichuris trichiura.
Non-biting cyclorrhaphan flies (Musca domestica, Chrysomya rufifacies, Musca sorbens, Lucina cuprina, Calliphora vicina, Chrysomya bezziana and Wohlfarthia magnifica) have been found to carry Trichuris trichiura. A study in two localized areas in Ethiopia found cockroaches were carriers for several human intestinal parasites, including Trichuris trichiura.
The exact incubation period of Trichuris trichiura is unknown, however immature eggs in soil under favorable conditions take about three weeks to mature: 15-30 days, 10 days minimum to mature before ideal ingestion by the human host. Favorable conditions for maturation of eggs is warm to temperate climates with adequate humidity or precipitation, as ova are resistant to cold, but not resistant to drying. Once ingested, the larva will remain dug into a villus in the small intestine for about 2-3 days until it is fully developed for migration to the ileo-cecum section of the gastrointestinal tract. The average total life span of Trichuris trichiura is one year, although there have been longer cases reported, lasting as long as five years (Note: inadequate treatment and re-infection are likely to play a role in this).
Adult worms are usually 3-5 cm long, with females being larger than males as is typical of nematodes. The thin, clear majority of the body (the anterior, whip-like end) is the esophagus, and it is the end that the worm threads into the mucosa of the colon. The widened, pinkish gray region of the body is the posterior, and it is the end that contains the parasite’s intestines and reproductive organs. Trichuris trichiura has characteristic football-shaped eggs, which are about 50-54 um long and contain polar plugs (also known as refractile prominences) at each end.
Unembryonated eggs (unsegmented) are passed in the feces of a previous host to the soil. In the soil, these eggs develop into a 2-cell stage (segmented egg) and then into an advanced cleavage stage. Once at this stage, the eggs embryonate and then become infective, a process that occurs in about 15 to 30 days). Next, the infective eggs are ingested by way of soil-contaminated hands or food and hatch inside the small intestine, releasing larvae into the gastrointestinal tract. These larvae burrow into a villus and develop into adults (over 2-3 days). They then migrate into the cecum and ascending colon where they thread their anterior portion (whip-like end) into the tissue mucosa and reside permanently for their year-long life span. About 60 to 70 days after infection, female adults begin to release unembryonated eggs (oviposit) into the cecum at a rate of 3,00 to 20,000 eggs per day, linking the life cycle to the start.
Typically, trichuriasis is diagnosed by identification of the typical eggs in a stool sample using the Kato-Katz thick-smear technique. Although colonoscopy is not typically used for diagnosis, as the adult worms can be overlooked, especially with imperfect colon, there have been reported cases in which colonoscopy has revealed adult worms. Colonoscopy can directly diagnose trichuriasis by identification of the threadlike form of worms with an attenuated, whip-like end. Colonoscopy has been shown to be a useful diagnostic tool, especially in patients infected by only a few male worms and with no eggs presenting in the stool sample.
Management and Therapy
An oral dose of 100 mg of Medendazole taken twice a day for two days or 500 mg in a single dose is the preferred treatment for Trichuriasis according to The Medical Letter (a non-profit organization that provides clinicians with a summary of drugs and dosages for the management of parasitic infections). An oral dose (taken with food) of 400 mg of Albendazole per day for three days or 200 mg per day for infants under 2 years old is used an alternative treatment. A second alternative treatment in an oral dose (taken on an empty stomach with water) of 200 mcg/kg of Ivermectin per day for three days. It should be noted that Ivermectin’s safety in children under 15 kg and pregnant women has not yet been established. Diarrheic patients may be treated with Imodium (loperamide hydrochloride) to increase the amount of drug contact with the parasites.
Age-standardised Disability-Adjusted life year (DALY) rates from Trichuriasis by country (per 100,000 inhabitants)
Note to Carlos: Please put the below legend next to the above map image (to the right)
less than 5
more than 60
Trichuris trichiura is the third most common nematode (roundworm) of humans. Infection of trichuris trichiura is most frequent in areas with tropical weather and poor sanitation practices. Trichuriasis occurs frequently in areas in which human feces is used as fertilizer or where defecation onto soil takes place. Trichuriasis infection prevalence is 50 to 80 percent in some regions of Asia (noted especially in China and Korea) and also occurs in rural areas of the southeastern United States. Infection is most prevalent among children, and in North America, infection occurs frequently in immigrants from tropical or sub-tropical regions. It is estimated that 600-800 million people are infected worldwide with 3.2 billion individuals at risk.
Public Health and Prevention Strategies/Vaccines
Improved facilities for feces disposal have decreased the incidence of whipworm. Handwashing before food handling, and avoiding ingestion of soil by thorough washing of food that may have been contaminated with egg-containing soil are other preventive measures. Mass Drug Administration (preventative chemotherapy) has had a positive effect on the disease burden of trichuriasis in East and West Africa, especially among children, who are at highest risk for infection. Improvement of Sewage and Sanitation systems, as well as improved facilities for feces disposal have helped to limit defecation onto soil and contain potentially infectious feces from bodily contact. A study in a Brazil Urban Centre demonstrated a significant reduction in prevalence and incidence of geohelminth infection, including trichuriasis, following implementation of a city-wide sanitation program. A 33% reduction in prevalence of trichuriasis and a 26% reduction in incidence of trichuriasis was found in the study performed on 890 children ages 7-14 years old within 24 different sentinel areas chosen to represent the varied environmental conditions throughout the city of Sao Paulo, Brazil. Control of Soil Fertilizers has helped eliminate the potential for contact with human fecal matter in fertilizer in soil.
Public Health Challenges still exist for the eradication of Trichuriasis. Limited access to essential medicine poses a public health challenge to proper treatment. Also, it is a public health concern that rates of post-treatment re-infection need to be determined and addressed to diminish the incidence of untreated re-infection. Lastly, with mass drug administration strategies and improved diagnosis and prompt treatment, detection of emergence of antihelmintic drug resistance should be examined.
Useful Web Links
John, David T. and Petri, William A.. Markell and Voge’s Medical Parasitology. Ninth Edition. Philadephia, PA: Saunder Elsevier, Inc., 2006. http://www.dpd.cdc.gov/dpdx/HTML/Trichuriasis.htm http://web.gideononline.com/web/epidemiology/ http://www.gastrointestinalatlas.com/English/Colon_and_Rectum/Parasites/parasites.html Joo JH,Ryu KH,Lee YH,Park CW,Cho JY,Kim YS,Lee JS,Lee MS,Hwang SG,Shim CS. “Colonoscopic diagnosis of whipworm infection.” Hepatogastroenterology 1998;45:2105–2109. Ok KS, Kim YS, Song JH, Lee JH, Ryu SH, Lee JH, Moon JS, Whang DH, Lee HK. “Trichuris trichiura Infection Diagnosed by Colonoscopy: Case Reports and Review of Literature.” Korean J Parasitol. 2009 Sep;47(3):275-280 “Trichuriasis.” Drugs for Parasitic Infection. New Rochelle, NY:The Medical Letter Inc., 2007. Hotez Peter J. M.D., Zheng Feng, Long-qi Xu, Ming-gang Chen, Shu-hua Xiao, Shu-xian Liu, Blair David, McManus Donald P., and Davis George M. “Emerging and Reemerging Helminthiases and the Public Health of China.” Emerging Infectious Disease. Volume 3, Number 3 (July-November 1997). Fetene T, Worku N. “Public health importance of non-biting cyclorrhaphan flies.” Trans R Soc Trop Med Hyg 2008 Sep 23. Kinfu A, Erko B. “Cockroaches as carriers of human intestinal parasites in two localities in Ethiopia.” Trans R Soc Trop Med Hyg 2008 Jun 23. Hotez Peter J. M.D., Molyneux David H Ph.D. D.Sc., Fenwick Alan Ph.D., Kumaresan Jacob M.B., B.S., D.P.H, Sachs Sonia Ehrlich M.D., Sachs Jeffrey D. Ph.D., and Savioli Lorenzo M.D. “Control of Neglected Tropical Diseases.” The New England Journal of Medicine 2007;357:1018:27. Mascarini-Serra L.M., Telles CA, Prado MS, Mattos SA, Strina A, Alcantara-Neves NM, and Barreto ML. “Reductions in the prevalence and incidence of geohelminth infections following a city-wide sanitation program in a Brazilian Urban Centre.” PLoS Neglected Tropical Diseases 2010 Feb 2; 4(2):c588. Nimir AR, Aziz MS, Tan GC, Shaker AR. “Massive lower gastrointestinal bleeding attributable to heavy whipworm infection and Salmonella typhi co-infection: a case report." Cases J. 2009 Sep 16;2:8285. Bickle QD, Solum J, Helmby H. “Chronic intestinal nematode infection exacerbates experimental Schistosoma mansoni infection.” Infect Immun. 2008 Dec;76(12):5802-9. Epub 2008 Sep 29. Whipworm Infection. MedlinePlus Medical Encyclopedia. US Federal Government public. domain. Update Date: 7/16/2004. Updated by: Daniel Levy, M.D., Ph.D., Infectious Diseases, Greater Baltimore Medical Center, Baltimore, MD. Review provided by VeriMed Healthcare Network. “Trichuriasis.” Drugs for Parasitic Infection. New Rochelle, NY:The Medical Letter Inc., 2007.