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Nematodes (Roundworms) Characteristics
- *Sensory organs (amphids) around head
- Unsegmented
- Bilaterally symmetrical
- Elongated
- Tapered at both ends
- Digestive tract is usually complete
- *most important to distinguish them
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Nematode Life Cycle Generalizations
Five states: one-cell--> morula--> vermiform embryo (pre-first state larvae)--> First State--> Second State--> Third State (usually infective state)--> Fourth State--> Fifth State (adult)-->
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Nematode Bursate
Posterior end of the male end. Baseball like structure that is used to clasp onto the females
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Nematode Non-bursate
Male does not have a bursate but does usually have a curved end which helps the male grab onto the female
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Spicules
On the end of the male worms that open up the females in order for sperm to be injected in
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Ascarids Morphology
- "Roundworms"
- Thick bodies
- Adults large, white
- They have three lips
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Ascarids Life Cycle Characteristics
- Females pass HUGE numbers of eggs
- Eggs are remarkably resistant to environmental degradation
- Infect young, immunologically naive animals
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Pathogenesis of Ascarids Migrating Larvae (normal path)
- Liver or kidney- scarring, hemorrhagic tract, "milk spots"
- Lung- antigenic pulmonary edema, 2-3 day old pups can die, nasal discharge in foals
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Pathogenesis of Ascarids Adult Worms
migrate from small intestine to stomach (causing vomiting)
Large numbers in intestine (mucoid diarrhea, pot-belly, contributes to malnutrition, painful, rough hair coat, fail to thrive)
May block bile duct
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Pathogenesis of Ascarids Aberrant Larval Migration
- Visceral larva migrans (VLM)
- Ocular larva migrans (OLM)
- CNS disease common
- Hepatomegaly, eosinophilia
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Diagnosis of Ascarids
- Adults
- Characteristic eggs on fecal float if patent
- Presumptive if within prepatent period (Clinical signs, gross apperance, age)
- Transtracheal aspirate in foal with respiratory disease due to ascarids
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Ascaris suum (host, site of infection, distribution)
- Intestinal large roundworm
- Host: pigs
- Site of infection: Adults in small intestines
- Distribution: Common, pigs raised outdoors
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Ascaris suum Life Cycle and Transmission Patterns
- Ingestion of infetive eggs (3rd State Larvae)
- Paratenic hosts: earthworms and dung beetles
- No transplacental or transmammary
- Prepatent period= 6-8 weeks
Hatches in stomach--> liver--> lungs--> swallowed--> Stomach
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Ascaris suum Pathogenesis due to migrating juveniles
Mechanical destruction of tissue- early infection (initial focal hemorrhages, respiratory distress)
Hypersensitivity (hyperemia, edema, eosinophilic infiltrates)
Fibrosis (milk spot lesions)
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Ascaris suum Parthogenesis Clinical signs due to adults
- Interference with proper nutrition and growth
- Diarrhea
- Occasional occlusion or perforation
- Subclinical effects- reduce growth rate
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Ascaris suum Diagnosis
- Patent infection: eggs in flotations, adults at necropsy
- During prepatent Period: respiratory signs in young pigs, feeder pigs 2 to 5 months
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Ascaris suum Eggs
50-70 by 40-60 in size, thick pitted outer wall, golden brown
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Parascaris equorum/ P. univalens (host, site of infection, distribution)
- Large intestinal roundworm or horse roundworm
- Host: equine species, horses and donkeys
- Site of infection: adults in small intestine, juveniles migrate extensively
- Distribution: common throughout the world
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Parascaris equorum Life Cycle
- Similar to A. suum (Hatches in small intestine--> liver--> lungs--> swallowed--> small intestine)
- Prepatent period: 10 weeks
- Prenatal infections are not known to occur
- Ingestion of infective eggs primary route
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Parascaris equorum pathogenesis migrating juveniles
- Respiratory distress and nasal discharge in foals
- Similar to the for A. suum
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Parascaris equorum pathogenesis adult worms
- moderate enteritis, colic
- subnormal growth
- dull hair coat
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Parascaris equorum diagnosis
Patent infections: eggs in flotations, adults at necropsy
- Prepatent infections: caughing and greyis-white nasal discharge in foal up to 6 months
- Endoscopy reveals frothy mucous in upper air passages
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Toxocara canis (host, site of infection, distribution)
- Host: canines
- Site of infection: adult in small intestines, juveniles migrate extensively
- Distribution: throughout the world, very common
- Have cervical alae (wings) on head
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Toxocara canis Life Cycle (Very important)
Puppy less than 5 weeks old ingests egg
L3 hatch in small intestines--> goes to liver--> lungs to aveoli--> goes to trachea to get swallowed--> stomach--> small intestine
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Toxocara canis Life Cycle (Very important) Transplacental
- Primary way that puppy becomes infected: Arrested larvae in the dams tissue-->Transplacental migration of L3 to fetal liver --> neonatal pup lungs (until puppy is born)--> lungs to aveoli--> goes to trachea to get swallowed--> stomach--> small intestine
- So efficient you can assume every puppy born is infected
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Toxocara canis Life Cycle (Very important) Mammary Glands transmission
- migration of L3s to mammary glands--> L3s ingested by sucking pups--> swallowed--> stomach--> small intestine
- (Rare)
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Toxocara canis Life Cycle (Very important) Paratenic Host
paratenic host ingests egg--> somatic migration L3 into tissue--> dog eats host and larvae released--> develops into an adult in intestines
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Toxocara canis Pathogenesis migrating juveniles
- Respiratory disease: 2-3 day old pups, transplacental transmission
- Heavy infection of worms in small intestine: nursing and weaned pups, pot-bellied pups, tender abdomens often due to bloating, pups will frequently whimper and cry
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Toxocara canis adult dogs
- Less susceptible:
- intestinal infection is rare in adult dogs but 5% of dogs 7 years of age in shelters were infected
- Puppies spontaneously purge intestinal infections as they mature and develop immunity to T. canis
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Toxocara cati (Host, Site of infection, Distribution)
- Large round worm of cats
- Host: Feline
- Site of Infection: adults in small intestine, juveniles migrate extensively
- Distribution: common throughout the world
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Toxocara cati Life Cycle
Transmission: ingestion of infective eggs, no prenatal infections, transmammary infections (maybe), ingestion of paratenic hosts important, prepatent period is 2 months
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Toxocara cati pathogenesis and disease
- respiratory signs in newborn kittens are absent
- nursing kittens may obtain heavy infections from transmammary transmissions
- clinical signs may include: abdominal distension and distress, chronic ill thrift
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Toxascaris leonina (host, site of infection, distribution)
- Roundworm
- Host: dogs, cats, foxes other wild carnivores
- Site of infection: small intestines
- Distribution: worldwide, uncommon in domestic dogs and cats, very common in wild carnivores
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Toxascaris leonina Life Cycle
- transmission: eggs embryonate in approximately 1 week
- may use mice as paratenic hosts
- does not require somatic migration like Toxocara canis
- no transplacental nor transmammary transmission
- Prepatent period: 2-2.5 months
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Toxascaris leonina pathogenesis
- not considered as pathogenic as Toxocara canis
- minor clinical significance, however, infected animals may be potbellied and unthrifty
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Toxocara vitulorum (host, site of infection, distribution)
- Host: cattle
- Site of infection: small intestines for adults, VLM in calves this is non-pathogenic
- Distribution: world wide but rare in US
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Baylisascaris spp. (hosts and importance)
- Hosts: wildlife, carnivores and omnivores
- Raccoon= Baylisascaris procyonis
- Importance: can also infect dogs, public health implications because of the close association of raccoon and humans
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