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Brief Summary

The nematode (roundworm) known as the Human Whipworm (Trichuris trichiura) is one of the most common geohelminths in the world affecting humans today ("geohelminths" are soil-transmitted parasitic nematodes with a life cycle involving no intermediate host or vector; they are transmitted via soil, food, or water that has been contaminated with feces from an infected host).Trichuris trichiura infects on the order of a billion people in the world. Symptoms are generally non-specific, with more serious conditions being much rarer. Disease severity is related to the intensity of infection (worm burden), with the most intense infection occurring in a minority of infected individuals. However, the bulk of the "disease burden" as measured by public health specialists is borne by the large number of moderately infected individuals with nonspecific symptoms. In typical infections, worms live relatively harmlessly in the caecum and appendix, with no larval migration through systemic tissue. However, even mild infections can affect fitness, growth, and cognitive abilities of the host. In heavy infections, worms spread throughout the colon to the rectum, where they cause abdominal pain, haemorrhages, mucopurulent stools, and symptoms of dysentery with rectal prolapse. (Chan 1997; Barker and Bundy 2000; Brooker 2010 and references therein) Brooker (2010) reviewed efforts to quantify morbidity and mortality from the major nematode intestinal parasites of humans: Trichuris trichiura, Ascaris lumbricoides, and the hookworms Necator americanus and Ancylostoma duodenale.

The unembryonated eggs of Trichuris trichiura are passed with the host's stool. In the soil, the eggs develop into a 2-cell stage, then an advanced cleavage stage, and then embryonate. Eggs become infective in 15 to 30 days. After ingestion by the host (via soil-contaminated hands or food), the eggs hatch in the small intestine and release larvae that mature and establish themselves as adults in the colon. The adult worms (approximately 4 cm in length) live in the cecum and ascending colon. The adult worms are fixed in that location, with the anterior portions threaded into the mucosa. The females begin to oviposit 60 to 70 days after infection. Female worms in the cecum shed between 3,000 and 20,000 eggs per day. The life span of the adults is about 1 year. Although the distribution of this parasite is worldwide, infections are more frequent in areas with tropical weather and poor sanitation practices and among children. (Centers for Disease Control Parasites and Health website)

The two most common intestinal parasites found in humans, Ascaris lumbricoides and Trichuris trichiura, are nearly always found together and archeological studies suggest that this association existed in historical North American and Old World contexts as well (although available paleoparasitological data suggest this may not have been the case in prehistoric South America, where evidence of A. lumbricoides eggs is less common). (Leles et al. 2010 and references therein)


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© Shapiro, Leo

Source: EOL Rapid Response Team

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