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Chapter 23 - Nematoda: Trichurida

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Title: Chapter 23 - Nematoda: Trichurida


1
Chapter 23 - Nematoda Trichurida
2
  • 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

3
  • 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

4
  • 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

5
Life Cycle of a Whipworm
6
  • 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

7
  • 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

8
  • 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

9
  • 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

10
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11
  • 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

12
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13
  • 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

14
  • 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

15
  • 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

16
  • 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
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