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Nematodes - Order Ascaridida
Terms in this set (25)
What are the 6 orders of Phylum Nematoda?
What are ascarids often called? Why shouldn't they be called this?
All the nematoda are round, not just ascarids!
What are the defining physical characteristics of ascarids?
Usually large, stout-bodied
Generally bigger than most other nematodes
Thick/strong cuticle, big, white (sometimes yellow)
Ascarids are highly successful in _____ vertebrate classes.
Highly successful in ALL vertebrate classes!
What kind of life cycle do ascarids have in domestic animals? Where do the adults typically live? Which sex is very prolific?
Direct life cycle
Adults live in the lumen of the SMALL INTESTINE
Typically between 5-40 cm long
Feed on lumen contents and host fluids
Females very prolific!
Do ascarids ATTACH in the host. small intestine?
NO! They do NOT attach.
ASCARIDS AIN'T ATTACHING!
The damage inflicted on the host is because they feed on the content in the small intestine - so they compete for nutrients with the hosts. They do NOT attach to the intestinal mucosa - so they don't cause damage that way.
Describe the "complicated" life cycle of ascarids - when is the egg infective? When does the infective larva hatch?
Eggs are passed in fresh feces as unembryonated, with a thick shell. These eggs are highly resistant to environmental conditions. Thus, disinfectants are largely ineffective and the eggs may survive for up to 2 years - no matter what the environmental conditions are!
Development of infective stage: 2-4 weeks
THE EGG IS NOT INFECTIVE UNTIL IT IS FULLY EMBRYONATED. So, the infective stage is NOT a larva. It is an egg with the larva INSIDE.
The infective larva does NOT hatch until the egg is SWALLOWED by the host - "don't be scared to swallow - with ascarids you gotta swallow!"
What does most of the literature say the infective stage for ascarids is?
The infective egg with the L2
THE EGG IS NOT INFECTIVE UNTIL IT IS FULLY EMBRYONATED - this means that all of the larval development is completed, and the infective larva will not hatch until the egg is swallowed by the a host.
How are ascarids diagnosed?
Eggs in feces - fecal flotation
Patent infections not usually hard to detect (so during the prepatent period we won't see eggs and usually the patient is asymptomatic).
With ascarids, what are some species differences in the life cycle?
1. Some species go straight to the intestine after ingestion by host and develop to adults
-A. galli in chickens
2. Some, including important mammalian species, have larval migratory phase in definitive host
-Parascaris spp in horses
-Toxocara spp in dogs and cats
What are the 2 species of equine ascarids? What are their defining characteristics?
1. Parascaris equorum
2. Parascaris univalens
Adults in small intestine
Males up to 30 cm, females are THICCCC up to 50 cm
What is special about the life cycle of equine ascarids? How long is the PPP?
Eggs passed in manure
Larvae hatch in the intestine and penetrate the intestinal wall
PPP about 3 months
Describe the hepatotracheal migration of equine ascarids.
The horse is infected when it ingests the infective/embryonated egg
Larvae hatch in the intestine and then penetrate the gut wall, and get into blood vessels that carry them to the liver
Carried to the liver in the blood
Enter hepatic portal system and go to the right heart
Leave right heart and reach lungs about 1 week post-infection
Coughed up and swallowed
Return to small intestine
What is the clinical importance of Parascaris - adults vs larvae?
Common in young horses
Low worm burdens may be subclinical
Adults in small intestine
-Competition with host for nutrients
-Poor condition, rough hair coat, pot belly (hypoproteinemia leads to edema, the enteritis leads to inflammation)
-Very heavy infection can lead to perforation or impaction
Larvae in lungs (heavy infection)
-Mechanical and inflammatory damage
-If all the larvae migrate at the same time, we can see pathology in the lungs, but this isn't common.
Patent Parascaris infections occur in ____ and ____ horses. Do adults usually have patent infections? How is this different from strongylid nematodies?
Foals and young horses (<2-3 years)
Immunity develops with age, so adults rarely have patent infections. Therefore, adults do NOT play a role in parasite transmission. This is different from strongylid nematodes, where even adult animals have some worms in the GI tract!
What is the common ascarid genus in small animal small intestines world wide? Dogs vs cats? Which one can infect both dogs AND cats?
Dogs and other canids: T. canis
Cats and other felids: T. cati
There are also other genus of ascarids in small animals - Toxascaris leonina - not common in the US - but can infect dogs AND cats.
What is the general life cycle of Toxocara canis? How does is differ from Parascaris?
Similar to Parascaris in the environmental portion
-Eggs passed in feces of infected animals (eggs very resistant/resilient to any environmental conditions)
-Take at least 3-4 weeks in environment to become infective
-Can survive long periods if protected from desiccation
Portion in host is MORE COMPLEX of a life cycle than Parascaris
When is hepatotracheal migration more likely vs somatic migration for Toxocora canis?
1. Hepatotracheal migration - greater proportion in dogs < 3 months of age, occurs in adults but a lower proportion
2. Somatic migration - more likely in older (> 3 months of age), more immune animals
What are the 4 routes of transmission for Toxocara canis?
1. Ingestion of infective eggs
3. Transmammary infection
4. Paratenic hosts
What is the clinical importance of Toxocara canis?
Most clinical signs seen in puppies
Low burdens = no or few signs
Moderate to heavy burdens - diarrhea/constipation, colic and pot belly, vomiting (worms can be seen), poor hair coat, intestinal obstruction, pneumonia
Looks like spaghetti in the vomit!
How is Toxocara canis diagnosed? Can the somatic reservoir be diagnosed?
Patent infections - fecal exam/flotation
We CANNOT diagnose a somatic presence of the worms - the dogs are a reservoir, and if they are female she will infect her litters.
What are the "big 3" of canine nematodes?
Prevalence depends on the population studied - vet clinic vs shelter going to be very different.
How does Toxocara cati different from Toxocara canis?
Somatic reservoir appears to be less important.
Some transmammary transmission occurs, but transplacental does NOT.
Not as clear differences in age with the life cycle as in T. canis, although it's more common in younger animals.
What is the public health significance of Toxocara? What are the 2 clinical disease syndromes?
Larvae can migrate in humans as in other vertebrates
Most infection asymptomatic
Clinical disease syndromes:
1. Visceral larva migrans (VLM) - larva anywhere
2. Ocular larva migrans (OLM) - in the eye
What are the other members of the Order Ascaridida?
1. Pigs (zoonotic) - Ascaris suum
2. Raccoons (zoonotic) - Baylisascaris procyonis
3. Humans - Ascaris lumbricoides
4. Cattle - Toxocara vitulorum
5. Poultry (don't migrate in ascarids) and other birds, reptiles, and fish
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