Ascaris lumbricoides

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Ascaris lumbricoides

• Suan Lui Teoh
• Danh Voong

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Introduction

• 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)

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Geography

• 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

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Host

• Definitive host Humans or pigs
• Intermediate Host -none-

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Modes of transmission

• 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

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Morphology

• Fertile egg
• mammillated
• thick external layer
• unembryonated
• measures 55-75 mm by 35-50 mm

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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

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Morphology Cont.

• Infertile

• Fertile

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EggCan survive for prolonged periods as long as
warm, shade, moist conditions are available and
can live up to 10 yearsEggs are resistant to
unusual methods of chemical water
purificationEggs are removed by filtration and
killed by boiling.Developing larvae are
destroyed by sunlight and desiccation
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Morphology Cont.

• Adult worm
• tapered ends length 15 to 35 cm
• Female are larger in size and have a genital
  girdle

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• The 3 prominent lips

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Life Cycle
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Life Cycle Cont.

• 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

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Cont.

1. Borrow out of blood vessels and enter bronchiols
2. Migrate through the lungs into the trachea
3. Enter throat and swallowed to end up in the small
   intestine
4. Mature and mate, where they complete their life
   cycle

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Food Habits

• 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

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Symptoms

• Symptoms associated with larvae migration
• 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)

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Symptoms Cont.

• Symptoms associated with adult parasite in the
  intestine
• Usually asymptomatic
• Abdominal discomfort, nausea in mild cases
• Malnutrition in host especially children in
  severe cases
• Sometimes fatality may occur when mass of worm
  blocks the intestine

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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 worms surface
• Adaptive Immune Response
• General consensus is a Th2 immune response with
  high IL-4 production, high levels of IgE,
  eosinophilia and mastocytosis

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Diagnosis

• Stool microscopy eggs may be seen on direct
  examination of feces.
• Eosinophilia eosinophilia can be found,
  particularly during larval migration through the
  lungs
• 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

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Treatment

• Mebendazole
• Albendazole
• Pyrantel pamoate
• Ivermectin
• Piperazine citrate
• Levamisole

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Prevention

• 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

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Some cool pictures
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How many people in the world are estimated to be
infected with A. lumbricoides ?
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Who are the definitive host/s of this parasite?
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Name 2 modes of transmission?
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What morphological difference can be seen in
fertile and infertile eggs?
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Name the symptom caused by larvae migration in
the lungs.
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What is the drug of choice for this parasite?
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What are some of the methods of prevention?
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