Download Intestinal Nematodes of Human Beings

Intestinal Nematodes
of Human Beings
Trichinella spiralis
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Diseases -Trichinosis, Trichiniasis,
Trichinelliasis
Morphology -the infrequently seen adult is a
small worm. It is characterized by:
Slender anterior end with a small, orbicular,
nonpapillated mouth
Posterior end bluntly rounded (female)
ventrally curved with two lobular caudal
appendages (male)
Single ovary with vulva in the anterior fifth
(female)
Long narrow digestive tract
• Trichinella spiralis larvae in
muscle section.
• A larva in a teased muscle preparation.
• Tail of male
Trichinella spiralis
• The adult worms
measure 1.5 mm (male)
to 3.5 mm (female) long
LIFE CYCLE
• Animals are infected with Trichinella spiralis when
they ingest infective larvae in raw or undercooked
meat. The larvae mature into adults in the host's
small intestine and the female worms give birth to
larvae. (The males die after fertilizing the females,
and the females die after producing larvae.) The
larvae enter the blood stream of the host and,
eventually, end up in the host's muscles. Here the
larvae mature into infective larvae, and the next
host is infected when it eats these larvae. In the
muscles the larvae cause a severe host reaction
that results in soreness and tenderness of the
muscles. Although this parasite probably only rarely
causes fatalities in humans, it can cause extreme
discomfort.
EPIDEMIOLOGY
• Infected persons in the world has been
greatly reduced. The prevalence of
Trichinosis is less in the tropics and
subtropics, chiefly owing to low
consumption of pork products,
religious bans on eating pork, Chinese
culinary custom of cooking it
thoroughly.
• People may also acquire the infection by the
ingestion of ground beef. Beef ground in a machine
in which infected pork has been ground is a
possible source of infection. Through an aggressive
program of meat inspection, the incidence of
trichinosis in pigs in the United States has been
lowered to less than 1%, so it is unlikely (but not
impossible) that pork products purchased in your
local supermarket will contain Trichinella
larvae. Most recent outbreaks of trichinosis in the
United States have been traced to pork products
from pigs that have not been inspected and that
have been slaughtered privately. Because of its low
host-specificity, almost any "wild" meat should be
considered suspect, and hunters should be careful
when preparing meat from their kills. In particular, a
number of infections have been traced to
contaminated bear meat.
PATHOLOGY
• The pathology of Trichinosis is
concerned with the presence of
larvae in the striated muscles and
vital organs and with the reaction of
the host to their activities. The muscle
fiber increased in size, become
edematous, develop a spindle shape
and undergo basophilic degeneration
• Common Diagnostic Test
Muscle biopsy, Antibody ELISA
• Clinical Signs:
Usually asymptomatic. Heavy
infections have been reported to
cause a hemorrhagic enteritis, muscle
pain and stiffness.
• Diagnostic Stage:
First stage-larva (arrows) in the nurse cell.
Larval cysts can get up to 3 mm in diameter.
TRICHURIS TRICHIURA
• Diseases –Trichuriasis, trichocephaliasis,
whipworm infection.
• LIFE CYCLE
The adults live in the host's large intestine with their
anterior ends embedded in the cells that line the
intestine; each female can produce in excess of 10,000
eggs each day, and the worms can live several
years. The eggs are passed in the host's feces, and
they become infective in about three weeks. When an
infective egg is eaten by the appropriate host it hatches
in the small intestine, and the worm migrates to the large
intestine where it reaches sexual maturity. Most
infections of whipworms are probably
asymptomatic. However, because the worms live a long
time and a person can be reinfected constantly, heavy
worm burdens can develop.
Trichuris trichiura adults.
Trichinella spiralis in tissue
Trichuris vulpis egg.
Trichuris trichiura in the
large intestine.
The posterior end of a male Trichuris sp.,
with an everted spicule