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Chapter 23 - Nematoda:
Trichurida
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
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
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
Life Cycle
of a
Whipworm
Epidemiology
• Most frequent in tropical countries
• In the US, it occurs predominantly in the southeastern states; it’s
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
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
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
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
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
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
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
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
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