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HomePage >> Textbook of Medical Parasitology >> Section Four Nematode
  | Contents | Section One: Introduction | Section Two: Trematode | Section Three: Tapeworm | Section Four: Nematode |               | Section Five: Larva migrans and accidental parasites of helminthes | Section Six: Protozoa | Section Seven: Medical arthropod |
III Trichuris trichiura (毛首鞭形线虫/鞭虫)

Objectives and Requirements
You should know the life cycle and morphology of T. trichiuras
know the pathogenesis and clinical manifestions caused by T.trichiuras infection.
be aware of the diagnostic methods of T.trichiuras
know the epidemiological characters and prevention measures of T.trichiuras infection.

Trichuris trichura, called whipworm also, is one of most common human parasites. Human infection with T.trichiura causes Trichuriasis. The condition is an intestinal infection caused by invasion of the mucosa of the colon by the adult worm. T.trichiura was first described by Linnaeus in 1771.

Adult worm    Adult worms are characteristically whip-shaped, the anterior three-fifth being long, thin and hair-like and the posterior one-to-two fifth being short, thick and stout. Males are slightly smaller than females, the latter measuring 35~50 mm in length. In both sexes, a capillary-like esophagus extends two-thirds of the body length and is encircled along much of its length by a series of unicellular glands. The cells can excrete some enzymes which possess antigenicity.
 Egg    The egg is typically barrel-shaped (纺锤状) with two polar plugs. These are yellowish brown and double shelled. The eggs are 50~54×22~23μm . The eggs contain an unsegmented ovum each, when passed in the feces. These freshly passed eggs are not infective to humans.

The life cycle of T.trichiura is simple, complete in a single host, the man. The change of host is needed for the continuation of species.
Adult whipworms occur primarily in the human host’s colon but also inhabit the appendix and rectum. The female deposits up to 1000 ~7000 eggs daily. After passed to the exterior in feces, the eggs develop slowly in warm, damp/moist soil. An unhatched, infective, third-stage larva develops in three to five weeks. New human hosts become infected when these embryonated eggs are ingested with contaminated food or water or from fingers. The larvae hatch in the upper portions of small intestine and quickly burrow into the cells of the intestinal villi, where they mature and undergo two molts in about 3-10days. Subsequently, they migrate to the caecal region and develop to sexual maturity in 30-90 days from the time the eggs were ingested. Adult worms embed the long, slender, anterior ends of their bodies deeply into the colon submucosa. These worms normally survive approximately 3-5 years in the human host.

Fig IⅤ-Ⅲ-1 Morphology and life cycle of Trichuris trichiura   

The major pathology resembles that of inflammatory bowel disease due to mechanical disruption and toxicity of whipworms. The pathological changes include hyperemia (充血), edema (水肿) or hemorrhage/bleeding (出血).  In few cases, there are cellular proliferation (细胞增生) and thickness of the intestinal wall causing inflammatory and granulomas .
Most infections are mild with no clinical symptoms. Chronic infections, however, produce symptoms such as bloody stools/chronic diarrhea, pain in the abdomen, weight loss, rectal prolapse (直肠脱垂), and anemia (贫血). It was reported that 73% of persons infected with whipworm were identified to be the cases of chronic colonitis by fibrescopy (纤维镜).

The clinical manifestations are not specific, so identification of eggs in fecal material constitutes diagnosis. It is based on the demonstration of the characteristic barrel-shaped eggs in the feces by light microscopy.

Whipworm infection occurs worldwide, most frequently in tropical countries. In China it is estimated that the prevalence of whipworms infection is 18.8%, and 212 million humans infected whipworms.
Warm climate (30℃), moist, dense shade, sufficient oxygen in soil are the environmental conditions for egg development. So the prevalence in south part is higher than in north part of China.
The species T. trichiura is almost exclusively a human parasite, with rare records of occurrence in other primates. Hand to mouth is a major way to acquire infection.

Mebendazole or albendazole, the drugs of choice, are most effective when administered orally for three consecutive days.
The control measures are similar to those measures for Ascaris control, health education and sanitation for example.

Reference reading articles
Stephenson LS, Holland CV, Cooper ES. The public health significance of Trichuris trichiura.Parasitology. 2000;121 Suppl:S73-95.
Mason NJ, Artis D, Hunter CA. New lessons from old pathogens: what parasitic infections have taught us about the role of nuclear factor-kappaB in the regulation of immunity.Immunol Rev. 2004 Oct;201:48-56.
Bradley JE, Jackson JA. Immunity, immunoregulation and the ecology of trichuriasis and ascariasis.Parasite Immunol. 2004 Nov-Dec;26(11-12):429-41.







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