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What are nematodes?
roundworms
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Define oviparous.
reproduce by depositing eggs
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Define larviparous.
reproduce by depositing larvae
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What is the life cycle of a nematode?
- egg
- 4 larval stages (L1, L2, L3, and L4)
- Immature adult (L5)
- Adult
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Describe the direct life cycle of nematode.
larvated (embryonated) egg ingested or L3 ingested, or enters through skin
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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
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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
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Name the different roundworms (ascarids)
- Ascaris suum
- Parascaris equorum
- Toxocara canis
- Toxocara cati
- Toxascaris leonina
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Describe the eggs of roundworms.
- very resistant in environment (dont' break down)
- sticky
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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
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What is the definitive and intermediate host for Ascaris suum?
- Definitive: pigs (accidentally cattle, sheep and humans)
- Intermediate: none
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What is the infection site of Ascaris suum?
- adult: small intestines
- larvae: liver, lungs; possibly spleen and kidneys
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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
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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
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How do you diagnose Ascaris suum?
oval ascarid egg
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What does an Ascaris suum egg look like?
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What is the definitive host and intermediate host for Parascaris equorum?
- definitive host: horses
- intermediate host: none
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What is the infection site for Parascaris equorum?
- Adults: small intestines
- Larvae: liver, lungs
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What is the pathogenesis for Parascaris equorum?
- effects foals less than a year old
- coughing
- nasal discharge
- poor/no weight gain
- intestinal impaction +/- rupture
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What is the definitive host and intermediate host for Toxocara canis?
- definitive: dog
- intermediate: none
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What is the infection site for Toxocara canis?
- adult: small intestine
- larvae: liver and lungs, other tissues
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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
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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)
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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
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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
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What is the pathogenesis for Toxocara canis?
- coughing
- verminous pneumonia
- intestinal obstruction
- colic
- distended abdomen
- eosinophilic granulomas in liver and lungs
- diarrhea
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Define larval migrans.
ingestion of egg by human
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What can larval migrans result in?
- visceral larval migrans
- ocular larval migrans
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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
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Describe ocular larval migrans.
- L2 migrates along optic tract to retina, humors
- usually seen in older children
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What are the clinical signs of visceral larval migrans.
- flu-like
- myalgia
- headache
- abdominal discomfort
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What are the clinical signs of ocular larval migrans?
swimming larvae
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How do we prevent larval migrans?
- clinic sanitation
- wash your hands
- don't eat in the lab
- good deworming practices
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What is the life cycle of Toxocara cati?
similar to Toxocara canis except: transplacental infection does not occur
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What are the paratenic hosts for Toxocara cati?
- mice
- chickens
- earthworms
- cockroaches
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What is the prevention for pregnant bitches agaisnt Toxocara canis?
Fenbendazole daily (50mg/kg) from day 40 of gestation to day 14 post partum
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What is the definitive host for Toxascaris leonina?
dogs and cats
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