Chapter 23 - Nematoda: Trichurida

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Chapter 23 - Nematoda Trichurida
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• Order Trichurida
• Family Trichuridae
• Often referred to as whipworms because they are
  threadlike along most of their body and then
  become thick at the posterior end

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• Trichuris trichiura
• In both sexes, a capillary like esophagus
  extends 2/3 of the body length and is encircled
  along much of its length by a series of
  unicellular glands, the stichocytes
• The posterior extremity of males is coiled and
  equipped with a single spicule enclosed in a
  spinose, retractile cuticular sheath

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• Life Cycle
• Adult worms occur primarily in the human colon
  but also inhabit the appendix and rectum
• Unembryonated eggs are passed to the exterior
  with the feces and develop slowly in warm, damp
  soil
• In about 3 weeks an unhatched eggs containing an
  infective, 3rd stage larva develops
• New human hosts become infected when these
  embryonated eggs are ingested with contaminated
  food or water
• Larvae hatch in the upper portions of the small
  intestine and quickly burrow into the cells of
  the intestinal villi near the crypts of
  Lieberkuhn, where they mature and molt in about 1
  week
• Later migrate to the caecal region, molting
  enroute, and develop into adults

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Life Cycle of a Whipworm
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• Epidemiology
• Most frequent in tropical countries
• In the US, it occurs predominantly in the
  southeastern states its the second most common
  nematode infecting humans (after Enterobius),
• The worm is found in areas with lots of rain,
  warm climate, dense shade and sanitary conditions
  that are conducive to soil pollution
• Children are more likely to be infected than
  adults because they are more likely to have have
  close physical contact with contaminated soil

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• Symptamology
• Most infections are light with no symptoms
• Chronic infections can produce symptoms such as
  bloody stools, pain in the lower abdomen, nausea
  and anemia
• Anemia may be the result of hemorrhaging when
  the worms penetrate the intestinal wall

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• Trichinella spiralis
• Males have curved posterior end with 2 lobed
  appendages called alae
• Single testis in the posterior part of the body
• Female with a bluntly rounded posterior end and
  one ovary
• Vulva in the anterior fifth of the body

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• Life Cycle
• Requires only 1 host in its life cycle (e.g.,
  one host can serve both as the definitive host
  and the intermediate host), with larvae and
  adults occurring in different organs
• Infections result from the consumption of meat
  containing encapsulated first stage larvae
• Once ingested these larvae are released into the
  duodenum by the action of host enzymes
• Larvae then penetrate the absorptive and goblet
  cells in the mucosa here they reach sexual
  maturity
• After copulation, the male passes out of the
  host, while the female borrows deeper into the
  mucosa and submucosa, entering the blood
  circulatory system
• Female then begins to deposit 1st stage larvae

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• Life Cycle cont.
• The female then dies, while the 1st stage larvae
  are carried by the lymphatic and blood vessels to
  the right side of the heart in the venous blood
• From the heart, the larvae enter the peripheral
  circulation and are carried to various tissues of
  the body
• In striated muscle, especially those of the
  diaphragm, jaws, tongue, larynx, and eyes, the
  larvae develop into the infective stage
• They penetrate muscle cells and establish
  themselves as intracellular parasites within
  myofibers

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• Life Cycle cont.
• They absorb nutrients from the host muscle and
  become surrounded by a nucleated mass known as a
  nurse cell
• The larvae are eventually encapsulated with
  collagen - enveloped by a double, ellipsoidal
  capsule of host origin

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• Life Cycle cont.
• Eventually the capsule become s calcified,
  anywhere from 6 months after the initial
  infection
• During capsule formation, the enclosed larva
  enters developmental arrest, a state in which it
  can survive almost indefinitely
• When muscle harboring the encapsulated larva is
  eaten by a carnivorous mammal, the larva excysts
  and reinitiates the life cycle

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• Epidemiology
• The term sylvatic trichinellosis denotes the
  cycling of the disease between wild carnivores
  and their prey or carrion
• Urban trichinellosis on the other hand, is the
  term used to designate the cycling of the disease
  among humans, rats, and pigs
• Rats and pigs feeding on garbage that includes
  infected pork waste, become infected in turn
• Dead or dying infected rats are themselves eaten
  by pigs
• Raw or poorly cooked pork (sausage) harboring
  infective larvae then becomes the vehicle for
  human infections
• Trichinellosis is a cosmopolitan disease that
  occurs most commonly in Europe and the US
• The disease is rare in the tropics for the
  opposite reason that it is found in the US a low
  consumption of pork and meat in general
• Also rare among Jews and Moslems

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• Symptomology and Diagnosis
• The primary symptoms of trichinellosis are the
  result of larval invasion of muscle and other
  tissue and the hyperimmune reaction of the host
  to the metabolic by-products and secretions of
  larvae
• During penetration of adult females into the
  mucosa there is nausea, perfuse perspiration and
  diarrhea
• During penetration and encapsulation of the
  larvae in muscle cells there is intense muscular
  pain, difficulty breathing, swelling of the
  facial muscles, etc
• Most of the cases of trichinellosis are
  asymptomatic and go undetected