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Ascaris (Round-worm)
 Distribution.
Spread widely in the world
Life
cycle.
Parasitic region is small intestine.
Eggs in soil with right conditions, such as temperature, and
humidity, develop into the infective larvae - Enter the body taken
into the mouth - Eggs are exuvially hatched out - The hatched larvae
actively migrated into the intestinal wall, then into the portal
circulation to liver, the right heart, and on into the pulmonary
vessels to the interalveolar tissues of the lungs - After growth and
essential develop in the lung, the larvae migrated or carried in the
mucus flow through the respiratory passage to the throat and are
swallowed.
Pathology
and Symptoms.
1. Due to Larva migrans
While Ascaris migrate into the intestinal wall or lung,
they cause bleeding by destroying capillary or
cause ascariasis pneumonia by secondary infection. Larva may
migrate into brain, spine, or kidney
through circuratory.
2. Due to the Larva
Larva take the nutrition from the small intestine, and
enzyme from the Larva inhibits digestion of the host and
causes symptoms such as indigestion, over- or in-appetence,
diarrhea, aneilema, cephalalgia, nausea, allergic symptoms such as
hives, cough, status asthmaticus, oliguria, and geophagia.
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Fertilized
egg |
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Fertilized,
Decorticated egg |
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Unfertilized egg |
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1¡8. Egg of Ascaris lumbricoides
: 1¡2. Fertilized egg ; 3. Unfertilized egg ; 6.
Decorticated egg of its outer albumin coat ; 7¡8.
Embryonated egg, including a larva in the egg shell ; 9¡10.
Adult female worms ; 11. Three lips at the mouth end, SEM view. |
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Causal Agent:
Ascaris
lumbricoides is the largest nematode (roundworm) parasitizing the
human intestine. (Adult females: 20 to 35 cm; adult male: 15 to 30
cm.)
Life Cycle:
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Ascaris lumbricoides
is an intestinal roundworm of huamns and is estimated to infect > 1500
million people (~1/4 of the worlds population). There is no
intermediate host, transmission being via ingestion of infective eggs
from e.g. raw food such as fruit and vegatables. It should be noted
that eggs can remain viable in the soil for many years.
Geographic Distribution:
The most common human
helminthic infection. Worldwide distribution. Highest prevalence in
tropical and subtropical regions, and areas with inadequate sanitation. |
The adult worms live in the lumen
of the small intestine. Females can produce upto 2,000,000 eggs per day
which are passed into the host's faeces. Outside the host, the eggs take
~14 days to mature into L1 stage larvae. After another week, the L1 larvae
devlop into the infective L2 stage larvae. Eggs are ingested by the host
and hatch in the small intestine. The L2 larvae then penetrate the tissues
of the intestine, enter the blood stream and migrate to the lungs. In the
lungs the L2 larvae moult twice to form the L4 larvae before entering the
pulmonary capillaries and making their way into the alveoli. At this stage
the larvae are reingested where they mature and mate to complete their
lifecycle.
Ascaris lumbricoides
is the largest nematode (roundworm) which parasitizees the human
intestine. Adult females are 20 to 35 cm in length, and adult males 15 to
30 cm.
Adult worms live in the lumen of
the small intestine. A female may produce approximately 200,000 eggs per
day, which are passed with the feces . Unfertilized eggs may be ingested
but are not infective. Fertile eggs embryonate and become infective after
18 days to several weeks , depending on the environmental conditions
(optimum: moist, warm, shaded soil). After infective eggs are swallowed,
the larvae hatch, invade the intestinal mucosa, and are carried via the
portal, then systemic circulation to the lungs. The larvae mature further
in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the
bronchial tree to the throat, and are swallowed. Upon reaching the small
intestine, they develop into adult worms. Between 2 and 3 months are
required from ingestion of the infective eggs to oviposition by the adult
female. Adult worms can live 1 to 2 years.
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A.lumbricoides:
partially decorticated egg;
the external layer of the capsule has lost part of its mammillated
layer |
A.lumbricoides
decorticated egg: normal fertile eggs may lack
the mammillated layer and are referred as decorticated eggs. |
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A.lumbricoides
unfertile egg: the unfertile eggs
are elongated
and much larger (85-95x43-47 µm); they have a thin shell, an irregular,
mammillated outer layer and a granular contents |
A.lumbricoides:
embryonated egg having a second stage (L2)
larva. |
SOURCE:
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Most of nematodes in the human intestine are maintained of their life
cycle by soil. The soil is indispensible for incubation and
transmission of eggs or larvae of the nematodes. These are Ascaris,
Trichuris, Strongyloides, and hookworm. They are highly prevalent
in developing countries at temperate zone as well as tropical zone,
and thus shoule be a major target in public health. |
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Ascaris
lumbricoides is the largest nematode (roundworm) parasitizing the
human intestine. (Adult females: 20 to 35 cm; adult male: 15 to 30
cm.) |
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A.lumbricoides
has a world-wide distribution and is most prevalent
in tropical areas. 25% of the world population harbours the parasite.
Life cycle. |
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