****************************************************
Introduction
Ascariasis is a disease caused by a parasite,
which is an organism that
depends
on another organism for its survival.
The specific parasite involved in
Ascariasis
is known as Ascaris lumbricoides. A.
lumbricoides is a type of
nematode or roundworm. It has also been referred to more commonly as the giant,
intestinal
roundworm. A. lumbricoides is
actually the largest intestinal roundworm
found
in humans. It is also one of the most
common parasites found in humans.
It
currently affects more than 1-1.5 billion people worldwide.
Most people harboring A. lumbricoides show no
signs of infection with
the
roundworm. Some people may show early
pulmonary symptoms and
eosinophilia
during the larval migration of the parasite.
Later on, some patients may
also
have abdominal symptoms. Occasionally, A.
lumbricoides can cause life-
threatening
disease from the worm bolus or ectopic migration of the worms. The worm
lives
in the upper part of the small intestine, and there are no reservoirs for the
parasite.
Some
effective drugs exist to treat the Ascaris.
A
picture of a female A. lumbricoides.
This roundworm was passed by a young girl living in Florida.
Image
taken from DPDx (Identification and diagnosis of Parasites
Of
Public Health Concern. http://www.cdc.gov/ncidod/dpd/parasites/ascaris
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Agent
The disease known as ascariasis is
caused specifically by the parasitic agent
Ascaris
lumbricoides. Occasionally, the swine ascarid, Ascaris
suum, can infect
humans
as well. It is still debated whether or
not A. lumbricoides and A. suum are
different
species.
A. lumbricoides is a type of organism grouped with other
helminthes or
worms. Three different phyla comprise the group
known as Helminths. There are
Cestodes,
which include blood parasites or flukes, Trematodes, which consist of
segmented
worms like tape worms, and Nematodes, which are roundworms like
Ascaris. Nematodes or roundworms are a type of
invertebrate, animals without
backbones. Specifically, nematodes are characterized by
their long, round bodies.
Common
parasitic roundworms apart from A. lumbricoides include: the pinworm,
the
hookworm, and the whipworm.
A.
lumbricoides gets its name from the earthworm Lumbricus terrestrias.
When
it was first discovered, this roundworm was called Lumbricus teres.
Here
is the specific classification of Ascaris lumbricoides:
Domain Eukarya
Phylum Nematoda
Order Asaridida
Family Ascaridoidea
Genus Ascaris
Species lumbricoides
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Synonyms
Ascaris is also known as a large,
intestinal roundworm.
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History of
Discovery
The anatomy of A. lumbricoides was
first described by Edward Tyson in
1683. However, at that time it was known as Lumbricus
teres not A. lumbricoides.
It
was actually Linnaeus, who renamed Ascaris and gave it its current name.
Linnaeus
named the roundworm Ascaris lumbricoides because it showed very
similar
morphology as that of the earthworm, Lumbricus terrestrias.
Then in 1917, Brayton Ransom and Winthrop Foster
were able to document
the
actual life cycle of Ascaris.
Afterwards in 1922, Shimesu Koino experimented
on
himself and his younger brother in order to describe the clinical disease
produced
by
Ascaris. Koino worked with both A.
lumbricoides and A. suum. He swallowed
2000
A. lumbricoides eggs, and he made his younger brother swallow 500 A.
suum
larvae. Koino became very ill for the experiment but
luckily no lasting damage
occurred,
and his brother did not suffer from as severe a disease. Specifically, in
this
daring self-experiment, Koino showed that a pneumonia-like syndrome can
develop
during early infection with Ascaris. He
also discovered that this syndrome
was
caused by migration of larvae through the lungs to the stomach.
***************************************************
Clinical
Presentation in Humans
Clinical Case Study
Taken from an article by C. Randall Clinch and LCDR
March B. Stephens.
“Case
description of Ascaris,” Arch Fam Med. 2000, 9; 1193-1194.
A 37-year-old man comes to your office after passing
something in his stool
that
he thought was a rubberband. He became
worried when he saw the object
moving
in the toilet. Apart from this
occurrence, he is a healthy man and is not
taking
any medications. He has had no recent
change in bowel habits or stool
appearance. He has not had fever, abdominal pain, cough
or rash. He does not
smoke,
drink alcohol, or use recreational drugs.
He has been physically active
and
recently completed a weeklong backcountry hiking expedition in the
Southeastern
U.S. Other than this expedition, he has
not been traveling recently.
With the clinical history and
presentation in mind the following are some
possible
diagnoses: 1) Ascaris lumbricoides (round worm) infection 2) Toxocara
(visceral
larva migrans) infection 3) Trichuris (whipworm) infection 4) rubberband
ingestion.
It turned out that this patient had Ascaris lumbricoides.
Clinical Correlation (Signs and Symptoms)
Ascariasis is the disease caused by
the parasite Ascaris lumbricoides.
Typically,
Ascaris infection does not cause visible disease. Most cases of Ascaris
infection
tend to be asymptomatic. Clinically
inapparent disease occurs with low
infection
of Ascaris, meaning that not many eggs are ingested. However, if hundreds
of
eggs are ingested, as seen in the early experiments by Shimesu Koino, the
patient
can
develop pneumonitis. Pneumonitis occurs
when the larvae migrate to the lungs.
This
pneumonitis also known as Loeffler’s syndrome, can appear four days to two
weeks
after infection occurs.
Some patients may also develop asthma, and the
asthma attacks can persist
until
worms are removed. Often times the
development of asthma in a nonsasthmatic
person
can be a clue of ascariasis. In
addition, liver enlargement and general toxicity
can
also occur during this period and persist for up to two weeks. Other health
problems
include fever, urticaria, malaise, nausea, vomiting, diarrhea, central nervous
system
disorders, and colic. Nutritional
problems that may develop can then lead to
abnormal
development in children.
While the worms are in the intestine, they can sometimes cause a life-
threatening
disease. If many worms are present,
they can become entangled and
form
a bolus, which blocks the lumen. Each
year two cases out of one thousand
have
been reported noting this severe intestinal obstruction. Another fatal condition
has
been reported where the worms have penetrated the small intestine leading to
acute
peritonitis.
In addition, adult worms can migrate
ectopically to the appendix, common
bile
duct, and pancreatic duct. This is
another life-threatening condition that is most
often
seen in small children with high parasite loads. As a result of the worm in the
biliary
duct, cholecystitis, cholangitis, hepatic abscess, and pancreatitis can
occur.
Suppuration
can follow from deterioration of the trapped worm and secondary
bacterial
infection.
General Summary of Symptom Timeline
Early phase (The early phase coincides with larval
tissue-migration. Typically,
4-16 days after egg ingestion.) The main symptoms include the following:
-fever
-cough
-wheeze
Late
Phase (The
late phase coincides with the mechanical effects of the worms.
These
include GI symptoms from mechanical irritation. Typically, 6-8 weeks
after
egg ingestion) The main symptoms
include the following:
-vague
abdominal complaints (cramping, nausea, vomiting)
-small
bowel obstruction (mainly in children)
-pancreatitis
(2ndary to worm migration)
-cholecystitis
(2ndary to worm migration)
-appendicitis
(less common, 2ndary to worm migration)
Multiple
Nematode infections. Four year old Puerto Rican patient
with
multiple parasites including Strongyloides stercoralis,, hookworm,
Ascaris
lumbricoides and Trichuris trichiura. He was small of stature
(equivalent
to 1 3/4 year old) and his weight was that of a 2 year old.
http://parasitepics.biosci.uga.edu
Ascaris in the small intestine. A. lumbricoides penetrating
the
http://parasitepics.biosci.uga.edu small
intestine causing an acute
condition known as
peritonitis.
Dr. Scott Smith’s lecture on ascariasis
Child
passing A. lumbricoides.
Bolus of A. lumbricoides passed from intestinal tract.
From Dr. Scott Smith’s The large mass was about 1.5 inches in length.
Lecture
on Ascariasis.
****************************************************
Transmission
A.
lumbricoides is transmitted primarily
through fecal-oral contamination.
The
transmission can occur by ingesting contaminated soil, water, or food. Usually,
ascariasis
is caused by directly or indirectly eating soil contaminated with feces
carrying
these eggs. These eggs mature in the
body, and adult female worms can
then
lay eggs that come out in the feces.
Note, however, that in order for the eggs
to
be infective or embryonated, the feces must have been infected 2-4 weeks before
it
is
ingested. Infection with Ascaris eggs
is so common because the eggs are frequently
found
in the environment due to poor sanitation practices and the use of night
fertilizer.
In addition to fecal-oral transmission of A.
lumbricoides, it is also believed
that
ascariasis can occur by way of trasnplacental transmission, since many
neonatal
cases have been documented.
It should be noted that Ascaris eggs
are some of the most resistant
existing
microorganisms. Their hearty egg shells
consist of four layers: ascaroside,
chitinous,
vitelline and uterine. The eggs are not
responsive to chlorine, high pH, low
pH,
and UV irradiation. They are resistant
to high and low temperatures. Alcohol,
ether,
and surfactants can inactivate the eggs.
In fact, Ascaris eggs can survive for
many
years in the soil.
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Life
Cycle
Adult worms reside in the upper part of the small
intestine, where they
survive
on predigested food. The worms make
themselves into an S-shape
and
press against the epithelium of the intestine while moving against the
peristalsis
to
keep themselves in the small intestine.
The female worm lays eggs, and she can
produce
up to 200,000 eggs per day. These eggs
are fertilized but
nonembryonated,
and the eggs are passed out with feces.
The
fertilized eggs develop through embryonation in feces deposited
in
the soil. The process of embryonation
takes 2-4 weeks. The eggs can survive
many
months before embryonation starts, but they need a moist aerobic
environment
to develop. The eggs are only infective
once they are embryonated
and
have larvae in them.
Once embryonated, the infective egg
must be swallowed to complete
the
life cycle of A. lumbricoides.
Bile salts and alkaline enteric juice of the small
intestine
stimulate the release of the larvae from the eggs. These second-stage larvae
then
travel from the small intestine to the liver.
Then the larvae migrate to the heart
via
pulmonary circulation. The larvae are
now third-stage larvae in the alveolar
capillaries,
and they enter the alveolar spaces.
Afterwards they migrate to the bronchi
into
the tranchea and then to the epiglottis.
The larvae are then swallowed, and they pass once
again to the small
intestine. There they molt twice and mature into adult
worms. The adult worms
can
live up to one year, and the females can lay eggs in the small intestine. However,
A.
lumbricoides
cannot reproduce in the intestine, and it can only lay eggs that are
not
yet infective.
Found
in Feachem et al, 1983
From
webpage by Kara Nelson.
Adult
worms 
live
in the lumen of the small intestine. A female may produce up
to
240,000 eggs per day, which are passed with the feces 
.
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.
Taken
from http://www.cdc.gov/ncidod/dpd/parasites/ascaris
****************************************************
Reservoir
No reservoir for this type of Ascaris
exists outside of humans. Pigs
have
their own type of Ascaris, which was mentioned previously.
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Vector
No vector exists for Ascaris.
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Incubation
Period
The appearance of early symptoms of
clinical disease can occur
anywhere
between 4-16 days after ingestion of the eggs.
Loeffler’s syndrome
and
other symptoms. Such as fever,
coughing, and wheezing take this long to
develop. However, GI symptoms take 6-8 weeks after
ingestion of the eggs to
develop.
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Morphology
Ascaris is a large intestinal
roundworm. It superficially resembles
the
common
earthworms found in the soil. Female
worms can be as long as 20-35
cms,
and males tend to be smaller, no larger than 30 cms. They can be anywhere
from
2-6 mm wide. Mature worms are
cylindrical, creamy white or light brown.
They
tend to have tapered ends.
The worms have a thick cuticle, 3 lips at its head,
small teeth, and its own
digestive
tract. The fertilized eggs are oval shaped,
and they are about 65 to 40
um
in size. The eggs are brown or yellow
brown, and they have a thick shell.
An
adult male (coiled posterior end) and a female A. lumbricoides.
Note
that the anterior ends are more slender than the posterior ends.
image taken from “A pictorial Presentation of Parasites”
http://parasitepics.biosci.uga.edu/CumulusCGI/Cumulus.acgi$KLS2672,105
This
picture shows the male and female worms.
The female shown is approximately
16
inches long.
Taken from P. Darben.
A
scanning electron micrograph picture taken of the
anterior
end of Ascaris. The three lips of the
worm are shown.
Taken
from “Wormland” site.
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Diagnostic Test
Diagnosis is usually not made
clinically based on signs and symptoms.
Sometimes
it can be diagnosed using ultrasonography and endoscopic
retrograde
cholangiopancreatography (ERCP).
Instead, diagnosis is made primarily by examining a
stool specimen.
Infection
with A. lumbricoides is determined by microscopic identification of
eggs
in the stool. Typically, the procedure
used involves the following:
1)
collecting stool specimen 2)
fixing specimen in 10% formalin
3)
concentrate using formalin-ethyl acetate sedimentation technique
4) examine wet mount of sediment
Occasionally, emergence of a worm in the stool or
coughed up can be used
to
diagnosis the patient.
Comparative
egg morphology for different Nematodes and Cestodes using in diagnostics.
A
picture of a fertilized egg.
Note
the rounded shape, Another picture of a fertilized
egg.
the thick shape, external mammilated Taken from “Atlas of Medical Parasitology.”
layer. (brown from bile).
http://www.cdc.gov/ncidod/dpd/parasites/ascaris
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Management and Therapy 
Image taken from Brian E. Keas
webpage on Ascaris lumbricoides.
People with Ascaris should be treated
regardless of the presence of
high
worm load, for ectopic migration of worms can cause life-threatening health
problems. The choice drugs for the treatment of
Ascaris infection are albendazole,
mebendazole,
and pyrantel pamoate. These drugs are
effective with few side-effects.
Mebendazole (Vermox) and Albedazole
are one class of drugs used to treat
Ascaris
infection. Mebendazole has often times
been considered the choice drug to
treat
intestinal roundworm infections. The
adult dose is 100 mg PO BID on 3
consecutive
days or 500 mg once. A second course is
administered if the patient is
not
cured in 3-4 weeks. Side-effects are
mild, but migratory activity has been reported
in
response to the drug. The dosage for
Albendazole is 400 mg once.
Pyrantel pamoate is also effective in
treating Ascaris. It can treat
other
nematodes, and it works by paralyzing the worms. The dosage is 11mg/kg once
(max.
1 gram).
Apart from the 3 drugs listed above, a few other
treatments exist. Yet, these are
choice
drug treatments listed by the CDC.
Levamisole hydrochloride is another type
of
drug used to treat Ascaris. This drug
has more side-effects than Mebendazole and
Pyrantel,
and it works by paralyzing the worm. In
addition, piperazine salts can also be
used
to treat Ascaris. Not many side-effects
have been noted, but they tend to be more
common
than other drugs available. They are
often times used because they are
cheap
and effective.
Courtesy Dr. Tom Nutman at the NIH
From Dr. Scott Smith’s lecture.
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Epidemiology
Ascariasis plagues more people in the
world than any other parasitic
infection. Some estimate that as many as 1-1.5 billion
people or approximately 1
out
of 4 people are infected with Ascaris.
In some tropical areas, 100% of the
population
have Ascaris.
Ascariasis tends to occur more commonly in places
where sanitation is
minimal
and human feces is used to fertilize crops.
As a result, the majority of
Ascaris
infections are concentrated in the developing world.
Approximately, 59 million people are at risk of
morbidity or clinical illness from
Ascaris. Children are more likely to be infected and
have higher levels of worms.
1.5
million children with Ascaris infections will suffer from irreversible growth
retardation. While death from Ascaris is rare,
approximately 10,000 people die from
Ascaris
each year.
Males tend to be more infected then
females, due to behavioral habits that
make
it more likely for them to ingest soil.
Some evidence of genetic predisposition
has
also been noted in a study of families in Nepal.
***************************************************
Country Information
Image taken from Brian E.
Keas webpage
on A. lumbricoides.
Ascaris is found all over the
world. However, it is most prevalent in
warm,
tropical
climates, where eggs can survive the longest in the soil. It is less common
in
places that are arid and seasonal.
Concentration of Ascaris seems to fall most
heavily
in South-EastAsia with less cases in Africa and Latin America. In South-East
Asia
approximately 73% of the people are infected.
India, Bangladesh, Burma,
Indonesia,
Malaysia, Philippines, Vietnam, China, Kenya, Tanzania, West Africa,
Turkey,
Iran, Afghanistan, Brazil, Columbia, Mexico, and Peru have all reported areas
where
Ascaris occurs in more than 50% of the local population living in these places.
Even in the U.S., many cases of
Ascaris occur. Approximately 4 million
people
in the U.S. are infected with Ascaris, and the majority of these cases are
concentrated
in the rural southeast part of the country.
**************************************************
Public Health and Prevention Strategies (Vaccines)
Prevention and control of Ascaris can
occur on two fronts: drug treatment
and
sanitation improvement. Mass
chemotherapy programs given every 6 months
can
help break the cycle of constant Ascaris infection. It is also important to educate
people
about adopting healthier living habits.
For instance, people can avoid eating
noncooked
vegetables and fruits in places lacking proper sanitation and areas that
use
human fertilizer. No vaccines are
currently in use to prevent the spread of this
parasite.
Listed
below are some of the World Health Organization’s listed combined
strategies
to control soil-transmitted helminthes such as A. lumbricoides:
1)
ensuring the wide availability of
single dose antihelminthic drugs
in all health services in
endemic areas
2)
ensuring good passive and active case management
3)
regularly treating at least 75% of all school-age children at
risk of morbidity by 2010
4)regularly
treating children at risk of morbidity through the IMCI strategy
5)improving
access to safe water and sanitation through intersectoral
collaboration
6)
improving hygiene behavior by scaling up sanitation education, targeted at
high-risk groups such as school-age children, women, and
special
occupation groups
Collection of
passed Ascaris from treatment project in school children.
Courtesy Dr. Tom
Nutman at the NIH
Dr. Scott Smith’s lecture
on Ascariasis
***************************************************
Useful Web
Links
http://www.cdc.gov/ncidod/dpd/parasites/ascaris
http://parasitepics.biosci.uga.edu
http://www.biosci.ohio-state.edu/~parasite/ascaris.html
http://vm.cfsan.fda.gov/~mow/chap30.html
http://www.path.cam.ac.uk/~schisto/Nematodes/Ascaris.html
http://www.nematode.net/Species.Summaries/Ascaris.lumbricoides/
http://www.medinfo.ufl.edu/year2/mmid/bms5300/bugs/asclum.html
http://www.ce.berkeley.edu/~nelson/ce210a/Ascaris/ascaris.htm
http://www.life.sci.qut.edu.au/LIFESCI/darben/nematode.htm
http://radiology.uchc.edu/eAtlas/GI/1208.htm
http://www.niaid.nih.gov/factsheets/roundwor.htm
***************************************************
References
Ascariasis
and its Public Health Significance.
Edited by DWT Crompton et al.
Medical
Parasitology. Markell, Voge, John 7th
and 8th edition (WB Saunders 1992)
http://www.cdc.gov/ncidod/dpd/parasites/ascaris
Handbook
of Medical Parasitology. Viqar Zaman
and Loh Ah Keong. 2nd
edition 1991 (Churchill Livingstone)
Parasitic
diseases. Dickson D. Despommier and
Robert W. Gwadz etc. 3rd
edition. (Springer-Werlag NY 1995)
http://www.dpd.cdc.gov/dpdx/HTML/Ascariasis.htm
http://parasitepics.biosci.uga.edu/CumulusCGI/Cumulus.acgi$KLS2672,105
http://www.biosci.ohio-state.edu/~parasite/ascaris.html
http://www.who.int/ctd/intpara/burdens.htm
http://www.who.int/infectious-disease-news/CDS2000/PDF/cd2000-e.pdf
****************************************************
Website
compiled by Kristina Adachi
For Dr. Scott Smith’s Human Biology Class 103: Parasites and
Pestilence
At Stanford University, Spring Quarter 2002
Questions? Email
adachik@stanford.edu