Transcript Ascaris lumbricoides - Winona State University

Ascaris lumbricoides
Suan Lui Teoh
Danh Voong
Introduction
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a common cream colored roundworm that
is parasitic in the intestines of humans
Most common helminthic human infection
Largest nematode to infect the human
intestine
An estimated 1 billion people are infected
(1 out of 4 people in the world)
Geography
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Worldwide
High prevalence in underdeveloped
countries that have poor sanitation (parts
of Asia, South America and Africa)
Occurs during rainy months, tropical and
subtropical countries
Even occurs in rural areas in the United
States
Host
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Definitive host : Humans or pigs
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Intermediate Host : -none-
Modes of transmission
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Occurs mainly via ingestion of water or food (raw vegetables or fruit
in particular) contaminated with A. lumbricoides eggs.
Occasionally inhalation of contaminated dust
Children playing in contaminated soil may acquire the parasite from
their hands
Enhanced by the fact that individuals can be asymptomatically
infected and continues to shed eggs for years
Prior infection does not confer protective immunity
Morphology
Fertile egg
 mammillated
 thick external layer
 unembryonated
 measures 55-75 mm
by 35-50 mm
Morphology Cont.
Infertile egg
 elongated and larger than
fertile egg
 thin shelled
 shell ranges from
irregular mammillations
to a relatively smooth
layer completely lacking
mammillations
 measures between 85-95
mm by 43-47 mm
Morphology Cont.
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Infertile
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Fertile
Egg
Can survive for prolonged periods as long as
warm, shade, moist conditions are available and
can live up to 10 years
Eggs are resistant to unusual methods of chemical
water purification
Eggs are removed by filtration and killed by
boiling.
Developing larvae are destroyed by sunlight and
desiccation
Morphology Cont.
Adult worm:
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tapered ends; length 15
to 35 cm
Female are larger in size
and have a genital girdle
The 3 prominent “lips”
Life Cycle
Life Cycle Cont.
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Females lay eggs in small intestine and eggs are
passed out through feces.
After 14 days, L1 larvae develops in eggs
L2 larvae develops after one week
Ingestion of raw foods, fruits or vege contaminated
with eggs will cause infection
Eggs hatch in small intestine, releases L2 rhabditiform
larvae
L2 penetrate intestinal wall, enter portal blood stream,
migrate to liver, heart and lungs in 1-7 days
Moults twice to become L4 larvae
Cont.
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Borrow out of blood vessels and enter bronchiols
Migrate through the lungs into the trachea
Enter throat and swallowed to end up in the small
intestine
Mature and mate, where they complete their life cycle
Food Habits
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Feeds on semi-digested contents in the
gut
Evidence show that they can bite the
intestinal mucus membrane and feed on
blood and tissue fluids
Symptoms
Symptoms associated with larvae migration
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Migration of larvae in lungs may cause hemorrhagic/
eosinophilic pneumonia, cough (Loeffler's Syndrome)
Breathing difficulties and fever
Complications caused by parasite proteins that are highly
allergenic - asthmatic attacks, pulmonary infiltration and
urticaria (hives)
Symptoms Cont.
Symptoms associated with adult parasite in the
intestine
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Usually asymptomatic
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Abdominal discomfort, nausea in mild cases
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Malnutrition in host especially children in severe cases
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Sometimes fatality may occur when mass of worm
blocks the intestine
HOST IMMUNE RESPONSE
Innate Immune Response
 Macrophage, neutrophils and most importantly
eosinophils
 The worms would be coated with IgG or IgE
which would increase the release of eosinophil
granules on the worm’s surface
Adaptive Immune Response
 General consensus is a Th2 immune response
with high IL-4 production, high levels of IgE,
eosinophilia and mastocytosis
Diagnosis
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Stool microscopy :eggs may be seen on direct examination of
feces.
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Eosinophilia: eosinophilia can be found, particularly during larval
migration through the lungs
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Imaging: In heavily infested individuals, particularly children, large
collections of worms may be detectable on plain film of the
abdomen.
Ultrasound: ultrasound exams can help to diagnose hepatobiliary
or pancreatic ascariasis. Single worms, bundles of worms, or
pseudotumor-like appearance, individual body segments of worms
may be seen.
Endoscopic Retrograde Cholangiopancreatography (ERCP) :
A duodenoscope with a snare to extract the worm out of the patient
Treatment
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Mebendazole
Albendazole
Pyrantel pamoate
Ivermectin
Piperazine citrate
Levamisole
Prevention
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Prevention of reinfection poses a substantial problem
since this parasite is abundant in soil – therefore good
sanitation is needed to prevent fecal contamination of
soil
Limit using human feces as fertilizer
Treatment can be done on contaminated soil although it
is not highly advised
Mass treatments of children with single doses of
mebendazole or albendazole – helps reduce transmission
in community but can cause reinfection
Some cool pictures
How many people in the world are
estimated to be infected with A.
lumbricoides ?
Who are the definitive host/s of this
parasite?
Name 2 modes of transmission?
What morphological difference can
be seen in fertile and infertile eggs?
Name the symptom caused by
larvae migration in the lungs.
What is the drug of choice for this
parasite?
What are some of the methods of
prevention?