Ascaris lumbricoid or Round worm
Ascaris lumbricoides cause ascariasis disease in human beings.
It is largest intestinal round worm parasite of human has worldwide destribution.
Morphology
Male worm measures about 15-25 cm in length and 3-4 mm in diameter.
Female worm measures 25-40cm in length and 5mm in diameter. The tail end conical and straight.
Source and mode of Transmission
Disease is transmitted by ingestion of soil containing parasite egg.
Infection occur only in single host i.e parasite larva grows in human intestine.
Infected with Ascariasis after, accidentally ingesting egg of ascaris lumbricoides.
Pathogenesis and clinical significance
When parasite egg ingested by human beings enter in intestine and release larva in intestine.
Symptoms
Abdominal pain
Colic pain
Poor digestion
Diarrhoea
Intestinal obstruction
Presence of larvae in lungs alveoli causes symptoms of pneumonia, pneumonitis (inflammed air sacs) allergic reaction, due to migrating larvae or due to adult worms.
This allergic reaction is due to ascaron (toxic substances produce by Ascaris).
Larva also cause hole forms of bowel, appendicitis and diverticulitis.
Mode of Infection
Infective form; Embryonated egg
Portal of entry; Alimentary canal
Site of location; small intestine
Life cycle
Ascaris lumbricoides passes it's life cycle in only one host. No intermediate host is required.
Man is only definitive host.
Human ingested infective fertilized egg, larvae of ascaris lumbricoides through contaminated food or water.
In human duodenum larvae is released from egg.
Larvae become young and very active.
Young larvae make hole in mucus membrane of small intestine.
From small intestine, young larvae enters in portal circulation to reach liver, then parasite enters in right side of heart through circulation.
After that from heart, larvae enters in pulmonary circulation where they grow in size.
From pulmonary circulation, larva reaches lung alveoli then enters in trachea.
From trachea parasite is pushed in larynx.
From larynx, parasites jump and are swallowed in pharynx.
In end, it enters in small intestine, as result larvae is converted into adult male and female worm and fertilization occurs.
Female worm discharges egg in stool, egg mature in soil, then again life cycle repeated on.
Human ingest infective egg of ascaris lumbricoides contaminated food and water.
In duodenum of human larvae is released from egg.
Young larvae penetrates mucus membrane of small intestine.
From small intestine larvae enters portal circulation to reach liver.
From liver parasite enter right side of heart through circulation.
From heart larvae enter in pulmonary circulation, grow in size twice.
From pulmonary circulation (young larvae reaches lung, alveoli, bronchi, trachea.
From trachea larvae pushes in larynx then pharynx.
Larva swallowed and reach intestine.
Larva convert into adult male and female worm.
Female worm discharging egg in stool, feces.
Develop in soil.
Laboratory Diagnosis
Specimen collection
Stool sample
Microscopic stool examination in normal saline
It show egg in feces.
Barium meal
Demonstrate presence of adult worms in small intestine.
X ray, Imaging
Diagnostic skin scratch test
Test include powdered ascaris antigen also called dermal reaction or allergic reaction for detection of ascariasis.
Treatment
Albendazole, mebendazole, decaris and pipeprazine are very effective.
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