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The round worm (Trichuris trichiura or Trichocephalus trichiuris) is a worm that causes trichuriasis 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.
The female T. trichiura produces 2,000–10,000 single-celled eggs per day. 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. 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 cecum and penetrate the mucosa and there they complete development to adult worms in the large intestine. The life cycle from time of ingestion of eggs to 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 can live up to five years, during which time females can lay up to 20,000 eggs per day.
Recent studies using genome-wide scan 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.
Trichuris trichiura has a narrow anterior esophageal end and shorter and thicker posterior anus. 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. 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.
There is a worldwide distribution of Trichuris trichiura, with an estimated 1 billion human infections. 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.
Infection occurs through ingestion of eggs (which are usually found in dry goods such as beans, rice, and various grains) and is more common in warmer areas. The eggs hatch in the small intestine, and then move into the wall of the small intestine and develop. On reaching adulthood, the thinner end (the front of the worm) burrows into the large intestine and the thicker end hangs into the lumen and mates with nearby worms. The females can grow to 50 mm (2 inches) long. Neither the male nor the female has much of a visible tail past the anus.
Mechanical damage to the mucosa may occur as well as toxic or inflammatory damage to the intestines of the host.
Trichuriasis can be diagnosed when T. trichiura eggs are detected in stool examination. Eggs will appear barrel-shaped and unembryonated, having bipolar plugs and a smooth shell. Rectal prolapse can be diagnosed easily using defecating proctogram and is one of many methods for imaging the parasitic infection. Sigmoidoscopy show characteristic white bodies of adult hanging from inflamed mucosa (coconut cake rectum).
Infection can be avoided by proper disposal of human feces, avoiding fecal contamination of food, not eating dirt, and avoiding crops fertilized with night soil. Simple and effective proper hygiene such as washing hands and food is recommended for control.
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Whipworms develop when a dog swallows whipworm eggs, passed from an infected dog. Symptoms may include diarrhea, anemia, and dehydration. The dog whipworm (Trichuris vulpis) is commonly found in the U.S. It is hard to detect at times, because the numbers of eggs shed are low, and they are shed in waves. Centrifugation is the preferred method. There are several preventives available by prescription from a veterinarian to prevent dogs from getting whipworm.
The cat whipworm is a rare parasite. In Europe, it is represented mostly by Trichuris campanula, and in North America it is Trichuris serrata more often. Whipworm eggs found in cats in North America must be differentiated from lungworms, and from mouse whipworm eggs just passing through.
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 (also called 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 and to a lesser extent ulcerative colitis 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, allergy, and other inflammatory disorders. Some scientific evidence suggests that the course of multiple sclerosis may be very favorably altered by helminth infection; TSO is being studied as a treatment for this disease.
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