Heartworm in Cats Flashcards
Pathogenesis of feline HW disease
Stage 1: inflammation
Stage 2: worm death
Stage 1 of feline HW disease
Inflammation
- arrival of immature worms in pulmonary arteries
- occlusive hypertrophy of small pulmonary arterioles
- 3-4 months post infection
- pulmonary inflammatory response “asthma-like” (HARD)
- live heartworms supress immune function, allows cats to tolerate infection until stage 2
Stage 2 of feline HW disease
worm death
- mature worms die and degenerate
- incites more pulmonary inflammation
- thromboembolism
- fatal acute long injury
- anaphylaxis
Heartworm Associated Respiratory Disease (HARD)
- substantial lesions in aterioles, arteries, alveoli, bronchioles
- induced by immature stages of infection even in absence of adult worms
- disease persists after elimination of parasites
feline HW disease is a lung disease not a heart disease
clincal signs of feline HW
- asymptomatic
- dyspnea
- vomiting
- cough
- sudden death
- neurologica
physical examination for feline HW
- may be normal
- heart murmurs are unusual and suggest primary cardiac disease (caval syndrome very uncommon)
- may have increased bronchovesicular sounds
- up to half of cats may present in respiratory distress or at least tachypnic
- neurologic signs
routine testing for feline HW
- usually not helpful
- CBC (may have increased eosinophils, basophils)
- chemistry panel (generally normal)
- urinalysis (generally normal)
- electrocardiography (usually normal)
microfilaria tests for cats
- microfilaremia in cats is rare
- transient 1-2 months
HW antigen tests in cats
- detect proteins shed from mature female worms
- not positive until 5-7 mos post-infection
- more specific, not as sensitive in cats
- positive test likely = HW infestation (but cats rarely test positive!)
- negative test
- male only and immature infestations more common
- need other diagnostics (Ab test)
HW antibody tests in cats
- detect antibodies to larvae and adults
- very sensitive, but not specific for presence of adult worms
-
negative test = unlikely HW infestation
- cat has not likely been exposed to D. immitis
- possibility for false positives
- previously resolved infestations, aberrant adult infestation
HW test result meanings:
positive Ag?
negative Ag?
positive Ab?
negative Ab?
positive Ag: current HW infestation, recently cleared infestation or false +
negative Ag: no HW present, pre-patent infestation (< 6mo), single sex infections, false negative
positive Ab: current HW infestation, previous exposure to HW or false positive
negative Ab: no exposure to HW, early infestation (<60 days), failure of cat to produce Ab or false negative
radiographs for dx of feline HW
- cardiac changes only seen in 50% of HW + cats
- cardiomegaly rarely seen
- right caudal lobar affected 1st
- pumonary artery blunting and tortuosity less common in cats than dogs
- right ventricular and main stem pulmonary artery enlargement uncommon
- most common abnormality noted = diffuse bronchial or bronchointerstitial pattern “asthma lungs”
echocardiography for dx of feline HW
- dependent on: skill, image quality, patient cooperation, location of worms
- positive in 30-80% of cats with HW
- differentiates primary cardiac disease from HW disease
- quantification difficult
asthma vs. heartworms in felines?
- presentation is the same: tachypnea/dyspnea
- thoracic radiographs: same
- labwork: same
- HW Ab & HW Ag: may help if one is positive, but only confirmatory if Ag +
- Echo: probably the biggest help (cost/availability)
Treatment is the same!
treatment of feline HW
- emergency therapy: O2, bronchodilators, steroids, supportive care/fluid therapy
- chronic therapy: inhaled/oral steroids, oral bronchodilators, doxycycline, ivermectine monthly
- surgical therapy/worm extraction
- adulticide administration
- not recommended in cats, toxic
