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Parasitology 2 > 6.13 – Nematodes IV – Spirurid Nematodes > Flashcards

6.13 – Nematodes IV – Spirurid Nematodes Flashcards

1
Q

Introduction to the Order Spirurida; what parasites are included, maun sites of infection, hosts

A
  • spirurids, filarids, guinea worm (Dracunculus)
  • mainly stomach worms, although some species in eyes or connective tissues
  • Physaloptera ‐ stomach worms of dogs
  • Spirocerca ‐ stomach worms of cats/dogs
  • Thelazia ‐ eye worms
  • Draschia/Habronema ‐ stomach worms of horses
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2
Q

Introduction to the Spirurids; General Life Cycle

A
  • all have indirect life cycles
  • use arthropodan intermediate hosts
    (copepods, insects, etc.)
  • paratenic hosts commonly used ‐ food chain
  • simple life cycle in definitive hosts (no complex migrations)
  • lengthy PPP’s
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3
Q

Stomach Worms of Horses ‐ Spirurids; what types, what type of life cycle, IH, transmission, site of infection

A
  • Habronema and Draschia spp.
  • indirect life cycles
  • use stable flies or house flies as IH
  • either L3’s or infected flies ingested
  • L3’s move directly to gastric pits and develop as adults
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4
Q

Habronema spp./Draschia megastoma; Pathogenesis/Lesions/Clinical Signs – Adult Worms

A
  • Habronema – chronic gastritis with mucus
  • Draschia – large tumour‐like nodules
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5
Q

Habronema spp./Draschia megastoma; Pathogenesis/Lesions/Clinical Signs – Larvae

A
  • larvae entering skin from fly proboscis are killed
  • inflammatory lesions – summer sores=ECH
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6
Q

Habronema spp./Draschia megastoma; treatment

A
  • no registered treatment against Draschia adults in lesions (and lesions largely asymptomatic)
  • adults of Habronema spp. – moxidectin, ivermectin
  • both Habronema and Draschia larvae in the skin can be treated with ivermectin
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7
Q

Introduction to the Filarids; General Features; type of parasite, host specificity, IH, sites of infection

A
  • spirurid nematodes
  • normally highly host‐specific
  • all require some blood‐sucking insect
    (often a dipteran fly) as an intermediate host
  • generally infect connective tissues or body cavities
  • long, slender adults at predilection site
  • tiny pre‐L1s (microfilaria) in blood or skin
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8
Q

Acanthocheilonema reconditum (= Dipetalonema reconditum); hosts, site of infection

A
  • typical filarid parasite of dogs that uses fleas (not flies) as the intermediate host
  • adults found in connective tissue
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9
Q

Acanthocheilonema reconditum (= Dipetalonema reconditum); morphology; adults and larvae

A
  • adults ‐ slender, about 5 cm in length
  • pre‐L1 (microfilaria) –
    240‐290 μm, with parallel‐sided anterior end (broomstick handle)
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10
Q

Acanthocheilonema reconditum (= Dipetalonema reconditum); life cycle

A
  • indirect life cycle ‐ requires fleas
  • microfilaria found in the blood of infected dogs
  • pre‐L1s develop to L3s and then re‐enter the dog by an unknown route
  • PPP = 2 months
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11
Q

Acanthocheilonema reconditum (= Dipetalonema reconditum); Pathogenesis/Lesions/Clinical Signs

A
  • non‐pathogenic, asymptomatic
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12
Q

Dirofilaria immitis

A

Heartworm

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13
Q

Dirofilaria immitis ‐ Heartworm; hosts, sites of infection, basic adult and larva morphology

A
  • typical filarid nematode
  • most commonly in dogs but can infect cats, ferrets, wild
    canids, sea lions, seals, humans
  • usually located in right caudal lobar artery,
    other branches of pulmonary arteries and, in heavy infections, right ventricle
  • adults ‐ slender, up to 35 cm long
  • larvae ‐ pre‐L1 (microfilaria), 290‐330 μm, tapered anterior end
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14
Q

Dirofilaria immitis ‐ Heartworm; life cycle

A
  • indirect life cycle
  • females deposit MF in blood
  • MF circulate in blood and may live for 2 yrs
  • mosquitoes ingest MF in blood meal
  • MF develop to L3s (the infective form) and migrate to the proboscis of the insect
  • development dependent on temperature above 14°C ‐ Implications for Canada?
  • heartworm transmission season is the period during which temperatures allow HW transmission
    (locally, June 1 to Oct 8)
  • this season lengthens as you move south
  • larvae migrate subcutaneously and eventually lodge in
    the pulmonary circulation
  • adults mature in pulmonary arteries (crowding from many worms may push them to ventricle)
  • PPP = 61⁄2 months
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15
Q

Dirofilaria immitis ‐ Heartworm; pathogenesis

A
  • blood vessels in the pulmonary circulation are damaged leading to inflammation and endothelial thickening (an arteritis)
  • worms that die give rise to thromboemboli in the lung capillaries and arterioles ‐ give inflammation (may be consolidation and fibrosis)
  • the above lesions give rise to increased vascular resistance leading to pulmonary hypertension
  • pulmonary hypertension can lead to right ventricular heart dilation, hypertrophy and congestive heart failure
  • pulmonary lesions give rise to respiratory signs
  • liver damage may result from venous congestion
  • damage may take some time to develop
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16
Q

Heartworm Diagnosis

A
  • recommend antigen test ‐ most sensitive
  • most dogs in Canada are asymptomatic
  • much more hype than parasites
  • difficult practitioner decisions
17
Q

Heartworm ‐ Microfilaria Tests

A
  • Knotts test or Difil
    ‐ both simple and relatively inexpensive
    ‐ only about 75% sensitive
    ‐ should differentiate Dirofilaria immitis from Acanthocheilonema reconditum
    (size and morphology of microfilaria)
    ‐ Dirofilaria much more common (>10X)
  • some dogs amicrofilaremic, but infected
18
Q

Heartworm ‐ Antigen Tests; how they work, sensitivity, specificity

A

Many different types but most depend on the production of a protein from reproductively active female worms (released, at most, a week or two before patency)

  • tests must be run EXACTLY as specified to produce expected sensitivity and specificity
  • tests generally have a sensitivity of >90% (10% of time false negative)
  • tests generally have a specificity of ~99% (1% of time false positive)
  • like all tests….predictive value varies with prevalence
19
Q

Heartworm ‐ Antigen Tests; limitations

A

‐ no use in prepatent period
‐ no use with senile worms
‐ no use with single worm infections
‐ no use with single sex infections

20
Q

Dirofilaria immitis ‐ Heartworm; treatments

A
  • adulticides
    ‐ Immiticide ‐ melarsomine (EDR only)
  • surgery
  • microfilaricides ‐ ivermectin ‐ 50 μg/kg
    ‐ milbemycin ‐ 500 μg/kg
  • preventatives ‐ ivermectin ‐ 6 μg/kg
    ‐ milbemycin ‐ 500 μg/kg
21
Q

Heartworm Disease in Cats

A
  • exceedingly rare (only one documented case acquired in southern Ontario)
  • more common in highly endemic regions
  • transient MF production ‐ most amicrofilaremic
  • more extensive clinical signs with fewer worms
    ‐ usually, chronic tachypnea and coughing, abnormal lung sounds, intermittent and chronic vomiting unrelated to eating

Parasitology 2 (6 decks)

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