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Cardiopulmonary Exam 1 > Heartworm in Dogs > Flashcards

Heartworm in Dogs Flashcards

1
Q

Heartworm life cycle

A
  1. mosquito bites heartworm infected dog and aquires microfilaria or L1 larva
  2. heartworm larve migrate to mosquito salivary gland undergoing 2 molts to become infective L3 larva (10-20 days)
  3. mosquito bites dog and infects dog with L3 heartworm larva
  4. larva develop and migrate through the tissues to the lungs where the L5 larval stage penetrate the blood vessels (45-60 days)
  5. adult heartworms in the pulmonary artery mate and produce new baby heartworm larva L1
  6. another dog is bitten by an infected mosquite and cycle starts over
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2
Q

pathophysiology of heartworms

A
  • pulmonary vascular effects
    • direct endothelial contact -> inflammatory mediators released -> Ag-Ab complexes -> dilation and blunting of pulmonary arteries
  • pulmonary parenchymal effects
    • local inflammatory response -> PMNs and Eos infiltrate parenchyma OR thromboembolism and embolism of dead worms
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3
Q

diagnosis of heartworms

A
  • blood tests
    • microfilarial tests
    • antigen tests
    • antibody tests
  • thoracic radiographs
  • +/- echocardiography
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4
Q

Heartworm antigen test

A
  • screening test of choice in dog
  • very sensitive and nearly 100% specific
    • detect Ag shed by mature females, can’t detect male only or immature infestations
  • usually a 4DX test (rickettsial diseases)
  • can be used to montior adulticide tx
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5
Q

when should heartworm antigen testing be done?

A
  • before starting prophylaxis (<6 months old)
  • no/inadequate prophylaxis
    • antigen and microfilaria test prior to starting prevention
  • adequate prophylaxis
    • antigen testing every year
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6
Q

heartworm microfilarial tests

A
  • blood smear-insensitive
  • Knott concentration- filter tests
    • 75% sensitive with patent infestations
    • not recommended asa sole screening test-only usually performed after a positive antigen test
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7
Q

what are the advantages of testing for Microfilaremia?

A
  1. validates a + antigen test
  2. identifies the patient as a reservoir of infection
  3. alerts you to the possibilty of severe reaction when using a microfiliaricide, and may alter your choice of medications
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8
Q

heartworm occult infestations

A
  • worm infestation without microfilaremia
  • prepatent- only L5
  • single sex infestations (cats)
  • immune destruction of microfilaria (cats)
  • macrocyclic lactone administration post infestation
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9
Q

What do these diagnostic results mean?

+ Ag, + microfilaria

+Ag, - microfilaria

puppy (<6mo) with microfilaria

A

patent HW infestation present

occult HW infesttion present

maternal transmission of L1, HW infestation not present

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10
Q

diagnosis of heartworms

A
  • clinical presentation
  • thoracic radiographs
  • echocardiography (dogs)
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11
Q

clinical presentation of heartworms

A
  • most dogs with heartworm disease are asymptomatic when diagnosed
  • dry, hacking cough
  • exercise intolerance
  • lethargy
  • caval syndrome
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12
Q

caval syndrome

A
  • “class 4”
  • worms become entwined in tricuspid apparatus
  • transient or sustained decrease in pulmonary BF allows worms to “fall” from the pulmonary artery to the right atrium
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13
Q

complications of caval syndrome

A
  • severe, acute tricuspid regurgitation
  • volume-overloaded right heart resulting in right-sided CHF
  • volume-underloaded left heart, decreased CO, and shock
  • shear stress of RBC’s across worms
    • intravascular hemolysis, hemoglobinemia, and hemoglobinuria
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14
Q

clinical signs of caval syndrome

A
  • sudden onset of severe lethargy
  • course right sided systolic murmur
  • dyspnea
  • pale mucous membranes
  • hemoglobinemia/hemoglobinuria
  • jugular pulsations
  • shock
  • +/- ascites, liver enlargement
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15
Q

treatment of caval syndrome

A
  • supportive care
  • surgical removal of worms
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16
Q

diagnosis of heartworms

A
  • thoracic radiographs
  • echocardiography
17
Q

thoracic radiographs for diagnosis of HW

A
  • can be normal
  • pulmonary arteries (enlargement, tortuosity)
    • caudal lobar arteries most often affected
  • lung parenchyma (interstitial to alveolar patterns)
  • right sided cardiomegaly
18
Q

echocardiography for diagnosis of HW

A
  • not necessary for work-up
  • not efficient method of dx, but can confirm caval syndrome
  • RV dilation or hypertrophy
  • tricuspid or pulmonic valve regurgitation
  • evidence of pulmonary hypertension
  • visualization of worms confirms dx
19
Q

classification scheme for HW disease

A
  • class 1, 2, 3
  • 1 mild, 3 severe
20
Q

pretreatment evaluation for HW

A
  • thorough history (clinical signs/energy level)
  • confirmatory heartworm test
  • CBC, chemistry, UA
    • ideal but not always necessary prior to tx
  • thoracic radiographs
    • severe changes: risk of post-adulticide complications
21
Q

Melarsomine (Immiticide)

A
  • only adulticide approved by FDA
  • deep IM injection
  • “fast kill” vs “slow kill”
22
Q

“fast kill” Immiticide

A
  • previously recommended for class 1-2 dogs
  • 2 injections 24 hours apart
  • no longer recommended (only special cases)
  • kills 90% of adult worms
23
Q

“slow kill” Immitide

A
  • split dose protocol
  • now recommended for all HW positive dogs
  • 1 injection
  • 1 month later, 2 injections 24 hours apart
  • kills 98% of adult worms
24
Q

side effects of Immiticide

A
  • pain inflammation at injection site
    • NSAIDs (not with Pred!)
  • allergic reaction
    • all dogs should be pre-treated with Benadryl
  • pulmonary inflammation/edema
  • mild cough, lethargy, fever
  • pulmonary thromboembolism
25
Q

Medications prior to adulticide therapy

A
  • doxycycline
  • macrocyclic lactones
  • +/- corticosteroids (if clinical signs warrant)
  • +/- antihistamines (if giving MLs and MF+)
  • aspirin (not indicated)
26
Q

doxycycline for HW

A
  • treatment for Wolbachia, an obligate, intracellular symbiotic bacteria harbored by D. Immitis
  • reduces Wolbachia in all stages of heartworms
  • supresses microfilaremia
  • may improve pulmonary and renal inflammation
  • should be give before adulticide
27
Q

macrocyclic lactones

A
  • controversial- potential resistance
    • give with doxy to further decrease MF
  • microfilariacide
  • treatment for 2-3 mos prior to adulticide
  • eliminates susceptibility gap created becomes of Mealrsomine’s unconfirmed efficacy against HW stages <4 mos
28
Q

post adulticide complications

A
  • pulmonary thromboembolism
    • worm fragments from dead worms lodge in distal pulmonary arterioles and capillary beds, blocking BF
  • clinical signs can range from asymptomatic to sudden death, but include cough, dyspnea, lethargy, pale mm, and collapse
  • risk increases with exercise, presence of radiographic changes or CS prior to therapy, concurrent pulmonary disease
29
Q
A
30
Q

treatment of PTE/pneumonitis

A
  • cage rest
  • steroid therapy
  • supportive care +/- hospitalization
  • O2 therapy
31
Q

Surgical extraction of HWs

A
  • most often indicated in life threatening caval syndrome
  • remove adults via jugular vein
  • blindly, fluoroscopic, or echo guidance
  • pros: improved survival, quick recovery, low complication risk
  • cons: anesthetic risk, expensive for clients, still need adulticide
32
Q

alternative HW therapies

A
  • long term macrocyclic lactone administration
  • macrocyclic lactone/doxycycline
33
Q

long term macrocyclic lactone administration for HW

A
  • “super slow kill”
  • not recommended
  • will shorten life span of adult worms, but may take ~2 years
  • strict rest still recommended for entire tx
  • continued pathology during tx course
  • debate about resistance
34
Q

macrocyclic/lactone doxycycline

A
  • reserved for cases when Melarsamine therapy is impossive
  • more rapid adulticidal therapy than MLs alone
  • decreases reproduction/sterilizes worms, so combo prevents microfilaria and transmission to other dogs
  • antigen test every 6 months
  • exercise restriction throughout the entire course of tx
35
Q

HW prevention

A
  • start no later than 8 weeks of age
  • test first if starting after 6 months or a dog that has missed prevention
    • if negative, repeat in 6 months
  • current available HW preventatives are macrocyclic lactones
36
Q

macrocyclic lactones

A
  • excellent therapeutic/toxic ratios
  • affect microfilaria, L3, L4, and young adult HWs (with continuous use)
  • nearly 100% effective when given according to label
  • Ivermectin (Heartgard), Milbemycin Oxime (Sentinel, Trifexis), Moxidectin (Pro Heart, Advantage Multi), Selamectin (Revolution)

Cardiopulmonary Exam 1 (10 decks)

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