NEMATODES Ascaris Lumbricoides

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NEMATODES Ascaris Lumbricoides
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NEMATODES (Round Worms)

• Ascaris lumbricoides (roundworm),
• Trichinella spiralis (trichinosis),
• Trichuris trichiura (whipworm),
• Enterobius vermicularis (pinworm),
• Strongyloides stercoralis (Cochin-china
  diarrhea),
• Ancylostoma duodenale and Necator americanes
  (hookworms)

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• Nematodes or roundworms are among the most
  abundant animals on earth - over 500,000 species
  have been described.
• Majority of nematodes are free-living in every
  conceivable habitat.

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Characteristics of the Phylum Nematoda
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Characteristics of the Phylum Nematoda

Reproductive system consists of tubular organs
lying in the pseudocoelom. MALE nematodes are
generally smaller in size.
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Characteristics of the Phylum Nematoda

FEMALE nematodes are larger in size. The female
reproductive organs are doubled.
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Characteristics of the Phylum Nematoda


Nematode development is similar in all
nematodes.  Consists of 4 larval (juvenile)
stages between the egg and adult. Each stage is
separated by a molt of the cuticle.  
M1 M2
M3 M4 Egg L1
L2 L3 L4
Adult Larval stages may be passed within the
egg, free-living in soil, parasitic in an
intermediate host, or parasitic in definitive
host.
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Ascaris Lumbricoides

• Ascaris lumbricoides , common saying round worm
  of man, is the largest of the intestinal
  nematodes parasitizing humans.
• It is the most common worm found in human.
• It is worldwide in distribution and most
  prevalent through out the tropics, sub-tropics
  and more prevalent in the countryside than in the
  city.

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Ascaris lumbricoides. The incidence is over
1500 million infections annually. Of these cases,
about 210 million are symptomatic. In some rural
settings with poor sanitation, perhaps half the
children of 2-12 years have ascariasis.Then
many of them will also have trichuriasis and
various of other chronic illnesses.
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I. Morphology

• Adult The adults are cylindrical in shape,
  creamy-white or pinkish in color.
• The female averages 20-35cm in length, the
  largest 49cm.
• The male is smaller, averaging 15-31cm in length
  and distinctly more slender than the female.
• The typical curled tail with a pair sickle like
  copulatory spines. On the tip of the head there
  are three lips, arranged as a Chinese word ? .

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• They have a complete digestive tract.
• Reproductive organs are tubular. male has a
  single reproductive tubule. The female has two
  reproductive tubules and the vulva is ventrally
  located at the posterior part of the anterior 1/3
  of the body.

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Adult worm of A. lumbricoides
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Ascaris lumbricoides
Female
Male
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Ascaris lumbricoides cont.
Female
gut
oviduct
genital pore
uterus
vagina
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Ascaris lumbricoides cont.
Male
sperm duct
seminal vesicle
testes
gut
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Lumbricus
A Worms Death
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Lumbricus cont.
clitellum
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Lumbricus cont.
seminal vesicle
spermathecae
crop
septa
gizzard
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Lumbricus cont.
Intestine with chlorogogue cells
septum
nephridium
ventral nerve cord
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The lips of Ascaris lumbricoides
The three lips are seen at the anterior end.
The margin of each lip is lined with minute teeth
which are not visible at this magnification.
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• Egg There are three kinds of the eggs. They are
  fertilized eggs, unfertilized eggs and
  decorticated eggs. We usually describe an egg in
  5 aspects size, color, shape, shell and content.

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1. Fertilized eggs broad oval in shape, brown
in color, an average size 60 45µm. The shell is
thicker and consists of ascaroside, chitinous
layer, fertilizing membrane and mammillated
albuminous coat stained brown by bile. The
content is a fertilized ovum. There is a
new-moon(crescent) shaped clear space at the each
end inside the shell.
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Fertilized Ascaris Egg

• A fertilized Ascaris egg, still at the
  unicellular stage, as they are when passed in
  stool. 

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• 2.Unfertilized egg Longer and slender than a
  fertilized egg. The chitinous layer and
  albuminous coat are thinner than those of the
  fertilized eggs without ascaroside and
  fertilizing membrane. The content is made of many
  refractable granules various in size.

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3. Decorticated eggs Both fertilized and
unfertilized eggs sometimes may lack their outer
albuminous coats and are colorless.
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II Life Cycle

• 1. Site of inhabitation small intestine
  
• 2. Infective stage embryonated eggs
• 3. Route of infection by mouth
• 4. No intermediate and reservoir
  hosts
• 5. Life span of the adult about 1
  year

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• This worm lives in the lumen of small intestine,
  feeding on the intestinal contents, where the
  fertilized female lays eggs.
• An adult female can produce approximately 240,000
  eggs per day, which are passed in feces.
• When passed, the eggs are unsegmented and require
  outside development of about three weeks until a
  motile embryo is formed within the egg.

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• After the ingestion of embryonated eggs in
  contaminated food or drink or from contaminated
  fingers, host digestive juices acts on the egg
  shell and liberate the larva into the small
  intestine.
• These larvae penetrate the intestinal mucosa and
  enter lymphatics and mesenteric vessels.
• They are carried by circulation to the liver,
  right heart and finally to the lungs where they
  penetrate the capillaries into the alveoli in
  which they molt twice and stay for 10-14days and
  then they are carried,

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• or migrate, up the bronchioles, bronchi, and
  trachea to the epiglottis.
• When swallowed, the larvae pass down into the
  small intestine where they develop into adults.
• The time from the ingestion of embryonated eggs
  to oviposition by the females is about 60-75
  days.
• The adult worms live for about one year. The
  ascarid life cycle is as the following diagram.

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• Ascaris lumbricoides worms have a reputation for
  wandering, and often do so if the body they are
  in-the host-is ill or taking certain medications.
  
• Adult roundworms sometimes spontaneously exit the
  host through the anus, mouth, or nose.
• They are found in the bathtub, toilet bowl, in
  diapers, or even on the pillow upon waking.

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III. Pathogenesis

• There are two phase in ascariasis
• 1. The blood-lung migration phase of the
  larvae During the migration through the lungs,
  the larvae may cause a pneumonia. The symptoms of
  the pneumonia are low fever, cough, blood-tinged
  sputum, asthma. Large numbers of worms may give
  rise to allergic symptoms. Eosionophilia is
  generally present. These clinical manifestation
  is also called Loefflers syndrome.

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• 2. The intestinal phase of the adults. The
  presence of a few adult worms in the lumen of the
  small intestine usually produces no symptoms, but
  may give rise to vague abdominal pains or
  intermittent colic, especially in children. A
  heavy worm burden can result in malnutrition.
  More serious manifestations have been observed.
  Wandering adults may block the appendical lumen
  or the common bile duct and even perforate the
  intestinal wall.

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• Thus complications of ascariasis, such as
  intestinal obstruction, appendicitis, biliary
  ascariasis, perforation of the intestine,
  cholecystitis, pancreatitis and peritonitis,
  etc., may occur, in which biliary ascariasis is
  the most common complication.

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Iii. Diagnosis

• The symptoms and signs are for reference only.
  The confirmative diagnosis depends on the
  recovery and identification of the worm or its
  egg.
• 1. Ascaris pneumonitis examination of
  sputum for Ascaris larvae is sometimes
  successful.
• 2. Intestinal ascariasis feces are examined
  for the ascaris eggs.
• (1) direct fecal film it is simple and
  effective. The eggs are easily found using this
  way due to a large number of the female
  oviposition, approximately 240,000 eggs per worm
  per day. So this method is the first choice.

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• (2) brine-floatation method
• (3) recovery of adult worms when adults or
  adolescents are found in feces or vomit and
  tissues and organs from the human infected with
  ascarids , the diagnosis may be defined.

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Ascaris
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Ascaris Worms in Intestine
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V. Epidemiology

• World wide distribution, very common in China,
  especially in the countryside.
• Factors favoring the spread of the transmission
• 1.  Simple life cycle.
• 2. Enormous egg production ( 240,000 eggs/ day/
  female ).

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• 3. These eggs are highly resistant to ordinary
  disinfectants( due to the ascroside). The eggs
  may remain viable for several years.
• 4. Social customs and living habits.
• 5. Disposal of feces is unsuitable.

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VI. Prevention and Treatment

• 1.Treatment to ascariasisMebendazole,
  Albendazole and Levamizole are effective.
• 2.Sanitary disposal of feces.
• 3.Hygienic habits such as cleaning of hands
  before meals.
• 4.Health education.

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