Nematode Overview & Ascarids

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  1. What are nematodes?
  2. Define oviparous.
    reproduce by depositing eggs
  3. Define larviparous.
    reproduce by depositing larvae
  4. What is the life cycle of a nematode?
    • egg
    • 4 larval stages (L1, L2, L3, and L4)
    • Immature adult (L5)
    • Adult
  5. Describe the direct life cycle of nematode.
    larvated (embryonated) egg ingested or L3 ingested, or enters through skin
  6. Describe the different types of nemaode transmission.
    • some species' eggs are ingested then develop into larvae
    • some species' larvae develop within egg, stay until ingested by the host
    • some species' larvae hatch (in an intermediate or paratenic host or the environment) and are ingested as larvae
    • some species' larvae enter environment and penetrate skin
    • some species' larvae are inoculated by a vector
  7. Define hypobiosis.
    • developmental arrest within a host
    • resting stage at some point in larval development, enabling them to survive adverse conditions while awaiting access to a new host
  8. Name the different roundworms (ascarids)
    • Ascaris suum
    • Parascaris equorum
    • Toxocara canis
    • Toxocara cati
    • Toxascaris leonina
  9. Describe the eggs of roundworms.
    • very resistant in environment (dont' break down)
    • sticky
  10. Describe the basic life cycle of ascarids.
    • egg ingested and hatches in intestines
    • larva burrows thru intestinal wall to portal circulation
    • goes to liver via blood
    • goes to lungs via blood
    • coughed up and then swallowed
    • go to intestines and mature
  11. What is the definitive and intermediate host for Ascaris suum?
    • Definitive: pigs (accidentally cattle, sheep and humans)
    • Intermediate: none
  12. What is the infection site of Ascaris suum?
    • adult: small intestines
    • larvae: liver, lungs; possibly spleen and kidneys
  13. What is the life cycle of Ascaris suum?
    • eggs hatch in small intestines and proceed to the liver via the portal vein
    • larvae molt and tunnel in the liver for several days
    • larvae then travel through the vasculature to the lungs
    • migrate through bronchial tree to the trachea then the pharynx
    • larvae are swallowed and mature in the small intestine
  14. What is the pathogenesis for Ascaris suum?
    • liver: milk spots, fibrosis
    • lungs: thumbs (heaves), pneumonia
    • intestinal obstruction
    • unthriftiness
    • failure to gain weight
    • signs worse in young animals
  15. How do you diagnose Ascaris suum?
    oval ascarid egg
  16. What does an Ascaris suum egg look like?
    • thick shell
    • wavy exterior
  17. What is the definitive host and intermediate host for Parascaris equorum?
    • definitive host: horses
    • intermediate host: none
  18. What is the infection site for Parascaris equorum?
    • Adults: small intestines
    • Larvae: liver, lungs
  19. What is the pathogenesis for Parascaris equorum?
    • effects foals less than a year old
    • coughing
    • nasal discharge
    • poor/no weight gain
    • intestinal impaction +/- rupture
  20. What is the definitive host and intermediate host for Toxocara canis?
    • definitive: dog
    • intermediate: none
  21. What is the infection site for Toxocara canis?
    • adult: small intestine
    • larvae: liver and lungs, other tissues
  22. What is the life cycle of Toxocara canis?
    • depends on the age of the dog
    • adult: uncomplicated intestinal cycle or somatic migration (hypobiosis)
    • puppy: tracheal migration
  23. Describe the uncomplicated intestinal life cycle for Toxocara canis?
    • eggs are passed and infective after 1 week
    • eggs containing larva or mice infected with larvae are ingested
    • larvae enter the wall of the small intestine and remain for 2 weeks
    • maturation takes place in the small intestine (no migration has occurred)
  24. Describe the tracheal migration life cycle for Toxocara canis.
    • effects puppies less than 3 months old
    • pup ingests eggs
    • larvae hatch in intestins and migrate to the liver then to the lungs
    • larvae then climb up the trachea
    • coughed up and swallowed to intestines and mature to adults
  25. Describe somatic migration (hypobiosis) life cycle for Toxocara canis.
    • effects dogs older than 3 months old
    • eggs are ingested and hatch in intestines
    • larvae migrate thru blood (liver, lungs) to tissues and encyst
    • if pregnant - excysts late in gestation
    • move to pups via transplacental or transmammary
  26. What is the pathogenesis for Toxocara canis?
    • coughing
    • verminous pneumonia
    • intestinal obstruction
    • colic
    • distended abdomen
    • eosinophilic granulomas in liver and lungs
    • diarrhea
  27. Define larval migrans.
    ingestion of egg by human
  28. What can larval migrans result in?
    • visceral larval migrans
    • ocular larval migrans
  29. Describe visceral larval migrans.
    • larvae hatch in small intestines
    • move from small intestines, liver, lungs, to somatic tissues
    • larvae migrate extensively then become quiescent
    • usually seen in children less than 4 years old - eating dirt
  30. Describe ocular larval migrans.
    • L2 migrates along optic tract to retina, humors
    • usually seen in older children
  31. What are the clinical signs of visceral larval migrans.
    • flu-like
    • myalgia
    • headache
    • abdominal discomfort
  32. What are the clinical signs of ocular larval migrans?
    swimming larvae
  33. How do we prevent larval migrans?
    • clinic sanitation
    • wash your hands
    • don't eat in the lab
    • good deworming practices
  34. What is the life cycle of Toxocara cati?
    similar to Toxocara canis except: transplacental infection does not occur
  35. What are the paratenic hosts for Toxocara cati?
    • mice
    • chickens
    • earthworms
    • cockroaches
  36. What is the prevention for pregnant bitches agaisnt Toxocara canis?
    Fenbendazole daily (50mg/kg) from day 40 of gestation to day 14 post partum
  37. What is the definitive host for Toxascaris leonina?
    dogs and cats
Card Set
Nematode Overview & Ascarids
Lab Tech
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