24 Questions
Where do adult worms of Ascaris lumbricoides live?
Small intestine of man
What is the diagnostic stage of Ascaris lumbricoides?
Immature fertilized egg
How many eggs can a fertilized female Ascaris lumbricoides lay in a day?
200,000 eggs/day
What is the mode of human infection of Ascaris lumbricoides?
Ingestion of raw green vegetables
Where do larvae migrate to after hatching in the small intestine?
Lung
What is the clinical manifestation of migrating larvae in the lung?
Allergic pneumonitis
What is the duration between infection and appearance of eggs in feces?
Two months
How can the worm be accidentally expelled?
Through vomits or stools
What is the primary habitat of the Ascaris lumbricoides worm?
Small intestine
What is the main difference between the male and female Ascaris lumbricoides worms?
Male is thinner and smaller than female
What is the primary method of diagnosis for Hymenolepis nana infection?
Examination of stool for eggs
What is the purpose of repeating treatment for Hymenolepis nana infection after 10-15 days?
To treat newly developed worms from hidden cysticercoid
What is the characteristic of the fertilized egg of Ascaris lumbricoides?
It is oval, brown, and has a course albuminous mamillated layer
What is the geographical distribution of Ascariasis?
More in warm developing countries with bad sanitation
What is the infective stage of the Schistosoma life cycle?
Furcocercus cercariae
What is the clinical picture of light Hymenolepis nana infection?
Asymptomatic
Where do the cercariae penetrate the human body?
During swimming or wading in infected water
What is the general body shape of Nematodes?
Bilaterally symmetrical, unsegmented, and cylindrical
Where do the adult worms finally settle in Schistosoma haematobium?
Vesical and pelvic plexus of veins
How do the eggs of Schistosoma spp. penetrate the wall of blood capillaries?
Through the action of both lytic enzymes and recoil of the venule
What is the final habitat of the adult worms in Schistosoma mansoni?
Mesenteric plexus of veins
In which part of the body do the eggs of Schistosoma haematobium finally reach?
Urinary bladder
What is the result of some eggs being trapped in tissues?
Bilharzial granuloma
What is the stage of the Schistosoma life cycle characterized by itching and dermatitis?
Stage of invasion
Study Notes
Ascaris lumbricoides (Round Worm)
- Habitat: Small intestine of man (Definitive host)
- Morphology:
- Adult worms: Long, creamy or pink in color, male is smaller and thinner than female
- Male: 20 cm in length, ventrally curved posterior end
- Female: 25 cm in length, straight posterior end
- Egg:
- Fertilized egg: Oval, brown, medium size, course albuminous mamillated layer, immature (contains one cell stage)
- Unfertilized egg: Elongated or irregular in shape, contain refractile granules, thin shell with weak mamillated layer
- Decorticated egg: Mamillated layer is lost
- Life cycle:
- Fertilized females lay immature fertilized eggs (Diagnostic stage) in feces (200,000 egg/female/day)
- Immature eggs develop in soil into embryonated eggs (Infective stage) in 2 weeks
- Embryonated eggs are ingested with contaminated food, water, or hands
- Eggs hatch in small intestine, liberating larvae
- Larvae penetrate intestinal wall, enter circulation, and migrate to lung, trachea, and finally back to small intestine
- Pathogenesis and clinical picture:
- Migration stage: Migrating larvae in lung may lead to allergic pneumonitis
- Intestinal stage: Adult worms may cause abdominal pain, nausea, vomiting, colic, or intestinal obstruction
- Diagnosis:
- Clinical diagnosis: Clinical picture
- Laboratory diagnosis: Finding eggs in feces, larvae in sputum, or accidental expulsion of worms in vomits or stools
Schistosoma spp. (Blood Fluke)
- Habitat: Vesical and pelvic plexus of veins (Schistosoma haematobium) or mesenteric plexus of veins (Schistosoma mansoni)
- Morphology:
- Cercariae (Infective stage): Develop in snail, penetrate human skin, and enter blood circulation
- Schistosomulae (Immature worms): Migrate to liver, mature, and pair up
- Life cycle:
- Cercariae penetrate human skin, enter blood circulation, and migrate to liver
- Male and female worms pair up, and female lays eggs in smaller capillaries
- Eggs penetrate blood capillary walls, reach urinary bladder (Schistosoma haematobium) or intestine (Schistosoma mansoni)
- Eggs exit with urine or feces, and reach fresh water to complete the life cycle
- Pathogenesis and clinical picture:
- Stage of invasion: Penetration of cercariae leads to itching and dermatitis
- Stage of migration: Immature worms in lung and liver cause allergic manifestations, fever, cough, and haemoptysis
- Liver becomes tender and enlarged
- Diagnosis:
- Clinical diagnosis: Clinical picture
- Laboratory diagnosis: Examination of stool or urine for eggs
Hymenolepis nana (Dwarf Tapeworm)
- Pathogenesis and clinical picture:
- Light infection: Asymptomatic
- Intestinal disturbance: Abdominal pain, diarrhea
- Severe infections: Insomnia, convulsions
- Diagnosis:
- Clinical diagnosis: Clinical picture
- Laboratory diagnosis: Examination of stool for eggs
- Treatment: Praziquantel, Niclosamide (Yomesan)
- Prevention and control:
- Treatment of patients
- Proper hygiene to prevent autoinfection
- Protection of food and drink from contamination with infected human feces
General Characteristics of Nematodes
- Bilaterally symmetrical, unsegmented, elongated, and cylindrical
- Separate sexes, males are smaller than females
- Body cavity contains body fluid, digestive and reproductive systems
- Nematodes infecting man can be divided into Intestinal and Tissue nematodes
This quiz covers the life cycle of intestinal worms, including the characteristics of unfertilized and decorticated eggs, and the role of the definitive host.
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