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