Page 864 - Cote clinical veterinary advisor dogs and cats 4th

Heartworm Disease, Cat 417

Initial Database ○ Heat treatment of serum dissociates Chronic Treatment
• CBC, chemistry profile, urinalysis immune complexes and appears to Preventive therapy is a safe and effective option
VetBooks.ir ○ Basophilia is highly suggestive but rare. Serum samples are heated to 103°C for for antigen and/or microfilaria is considered Diseases and Disorders
○ Mild nonregenerative anemia or eosino-
for the prevention of HWI in cats. Pretesting
increase the sensitivity of antigen tests.
philia in about 33%
10 minutes, the resulting coagulum is
unnecessary.
centrifuged, and the supernatant is tested.
○ Microalbuminuria and proteinuria second-
ary to glomerular disease possible • Echocardiography (p. 1094) • Ivermectin (Heartgard for Cats): 25 mcg/
kg PO monthly, or
• Tracheal wash or bronchoalveolar lavage ○ Dilated pulmonary arteries • Selamectin (Revolution): 6-12 mg/kg topi-
may contain eosinophils with or without the ○ Parallel linear hyperechoic densities in cally monthly, or
presence of peripheral eosinophilia (similar pulmonary arteries, the right heart, and/ • Imidacloprid-moxidectin (Advantage Multi):
to allergic asthma or lungworms). or the venae cavae represent heartworms 10 mg/kg imidacloprid and 1 mg/kg mox-
• Fecal exam for lung parasites (flotation, ○ Heartworms identified in 40% and 78% of idectin applied monthly
sedimentation, Baermann procedure) naturally infected cats in two small studies Chronic treatment of HWI:
• Imaging • Electrocardiography may demonstrate a • Continue one of the above preventatives
○ Thoracic radiographs (findings depend on right axis shift and/or atrial or ventricular • Doxycycline 5 mg/kg PO q 12h × 4 weeks
duration of infection and HWI severity). arrhythmias in severe cases (uncommon). can be considered empirically. Precautions
Enlarged and sometimes tortuous, should be taken to avoid esophagitis.
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truncated caudal pulmonary arteries. TREATMENT CHF:
Right heart enlargement, common in • As described on pp. 408 and 409.
dogs, is unusual in cats. Treatment Overview • Sildenafil 1 mg/kg PO q 8h can be
Patchy mixed interstitial-alveolar pattern • Address complications. used empirically to reduce pulmonary
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with perivascular infiltrates (primarily • Prevent future infection. hypertension.
in caudal lung lobes) • Aggressive adulticidal therapy is generally Eosinophilic pneumonitis/HARD:
Radiographic vascular findings may be not recommended. • Corticosteroids: prednisolone 0.5-1 mg/kg
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transient. ○ There is no role for melarsomine in cats. PO q 24h, tapering over 4 weeks; reinstitute
Mimics asthma with bronchovascular ○ A slow-kill approach has logic in that it as needed at lowest q 48h dosage that
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pattern and possibly pulmonary protects from future infection and rids maintains the cat free of clinical signs
hyperinflation (controversial) the cat of adult worms gradually. • For cats that can be tapered to alternate-
day steroids, consider transition to
Advanced or Confirmatory Testing Acute General Treatment fluticasone 110-220 mcg by metered-dose
• The diagnosis of HWI/HWD in cats can • Cats with HWD should receive HWI- inhaler with spacer and face mask, 1 puff q
be difficult and often requires an elevated preventive medication (see Chronic Treat- 12h.
index of suspicion and serial application of ment below); short-term corticosteroid • Albuterol 90 mcg by metered-dose inhaler
diagnostic tests. therapy (prednisone 0.5-1 mg/kg PO q 24h) with spacer and face mask can be used at
• Microfilariae: most cats are amicrofilaremic. may be used for managing respiratory signs. home in case of respiratory distress (1 puff
Filter and modified Knott’s tests are preferred • Emergency therapy for acute dyspnea: every 30 minutes for up to 4 hours).
over wet direct blood smear. A positive result ○ Oxygen therapy (oxygen cage at 40% O 2
is uncommon but diagnostic. or nasal insufflation at 50-100 mL/kg/min Possible Complications
• Heartworm antibody tests [p. 1146]) Chronic corticosteroid therapy is diabetogenic
○ Used in the detection of exposure to ○ Cage rest in cats.
heartworms and possible HARD or ○ Corticosteroids (dexamethasone 0.125 to
mature HWI; does not prove ongoing 0.5 mg IV or IM, repeat q 24h as neces- Recommended Monitoring
infection sary or prednisolone sodium phosphate Every 6-12 months, if stable (perhaps only by
○ In addition to multiple send-off options, or succinate 1 to 2 mg/kg IV q 24h) telephone, if financial concerns)
a point-of-care test is available (Solo Step, ○ Bronchodilator therapy (terbutaline
Heska, Loveland, CO). 0.01 mg/kg SQ or IM, or aminophyl- PROGNOSIS & OUTCOME
○ Although used as a screening test, up to line 2-5 mg/kg IV slow infusion over
14% of cats with mature HWI may be 30-60 min) • Fair for asymptomatic HWI
antibody negative. Approximately 2% of ○ Antithrombotic therapy: aspirin (80 mg • Guarded for the remainder of non-CHF and
heartworm-infected, antibody-negative PO q 72h) is controversial. Clopidogrel non-ARDS patients
cats are heartworm antigen positive. recently was shown to be superior to • Grave for ARDS
• Heartworm antigen tests (ELISA and aspirin as an antiplatelet agent in cats • Guarded for CHF; worm retrieval may
immunochromatographic; assess for antigen (18.75 mg/CAT PO q 24h). help
elaborated by adult female heartworms) are • Worm extraction • Overall, beyond day 1, the prognosis for cats
specific, and some are semiquantitative. A ○ Historically, mortality rates in one report with HWI is similar (median survival, 4.5
positive result is diagnostic. (2 of 5 cats died) made this option years) to that for hypertrophic cardiomyopa-
○ High number of false-negative results due unappealing, but the use of newer, less thy (median survival, 6.5 years), which shares
to low female worm burdens, immature traumatic catheter devices such as micro- a median age at diagnosis of approximately
infections, and possibly immune complex snare kits has proved successful in a small 6 years.
(antigen-antibody) formation number of cases, likely due to reduced • For most patients surviving the initial
○ A feline-specific antigen test has been anaphylaxis from worm trauma. insult, median survival is much greater
marketed (adaptation of the canine test • Microfilaricide therapy than 1 year. Acute decompensation and
with reported 15% increase in sensitivity ○ No agent is currently approved by the even death can occur, however, in any
[IDEXX SNAP Feline Heartworm Antigen U.S. Food and Drug Administration for heartworm-infected cat, regardless of initial
test, Westbrook, ME]). the elimination of microfilaria. presentation.
○ Clinical signs can and often do occur before ○ The authors’ recommendation for micro- • Studies suggest that some cats remain
the presence of detectable heartworm filaricidal therapy is to initiate macrolide asymptomatic and self-cure, with the infec-
antigen. prophylactic therapy at the time of diagnosis. tion unrecognized.

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