Page 863 - Cote clinical veterinary advisor dogs and cats 4th

416 Heartworm Disease, Cat

RISK FACTORS Clinical Presentation ○ Pulmonary arterial medial and intimal
• Cats not receiving a heartworm preventive DISEASE FORMS/SUBTYPES hypertrophy with or without thrombosis,
VetBooks.ir individual risks determined by time spent 2) acute or peracute, and 3) chronic (most ○ Altered vascular permeability allows plasma
often resulting in obliteration of the
in endemic areas are at risk, with various
• Clinical classification: 1) no clinical signs,
vascular lumen
outdoors, season of the year, and geographic
common)
location.
defined as an infection in which microfilariae
nary edema (ARDS), which is typically
• Outdoor cats are predisposed, but indoor • Most feline HWIs are occult infections, leakage, producing noncardiogenic pulmo-
cats are also at risk (up to one-fourth of are not detectable; microfilaremia in cats fatal.
cats with HWI are reported to be indoor is uncommon (<20%), inconsistent, and ○ Chronic changes can result in diminished
cats). transient. pulmonary function, hypoxemia, dyspnea,
• Feline leukemia virus and feline immu- and cough.
nodeficiency virus are not predisposing HISTORY, CHIEF COMPLAINT • Acute or sudden death of affected cats is
factors. • About 28% of cats with HWI show no typically associated with adult worm death
clinical signs of HWD. and resultant respiratory failure.
CONTAGION AND ZOONOSIS • Chronic signs usually predominate (cough ○ Lungs are considered to be the shock organ
Cats with mature HWI are rarely microfila- [38%]; dyspnea [48%], vomiting, anorexia, in cats.
remic, and the likelihood of transmission to weight loss, lethargy, exercise intolerance, ○ Immune-mediated reaction to heartworm
other cats, dogs, or humans is low (p. 418). and rarely right-sided CHF). antigens produces bronchiolar and bron-
• Acute signs include tachypnea/dyspnea chial constriction, pulmonary congestion
GEOGRAPHY AND SEASONALITY secondary to PTE, severe pneumonitis, or and interstitial edema, acute inflammatory
• The prevalence of feline HWI correlates with ARDS. Sudden death in ≈10%. interstitial disease, superficial pulmonary
that of dogs in the same geographic region hemorrhage, and periarterial hemor-
(5%-15% that of dogs). PHYSICAL EXAM FINDINGS rhage with subsequent fatal respiratory
• Reported worldwide and is variously endemic • Usually nonspecific. There appears to be failure.
in most parts of the United States little correlation between the clinical signs, ○ Heartworm embolism
• Heartworm transmission is unlikely in regions physical exam findings, and radiographic ■ Smaller feline pulmonary arterial
or seasons where the ambient temperature changes. tree with less collateral circulation is
does not average more than 65°F (>18°C) • Adventitial lung sounds may be heard. more susceptible to worm emboliza-
during a 30-day period. • An audible heart murmur and/or gallop tion with subsequent pulmonary
• Prevalence: up to 14% in shelter cats and sound is uncommon, and CHF is rare. infarction.
9% in pet cats presented for cardiorespiratory Jugular venous distention (often with pulsa- ■ May contribute to episodes of dyspnea
signs (26% of these cats were heartworm tion), dyspnea, diminished lung sounds, and and/or sudden death
antibody positive, indicating heartworm (rarely) ascites may be detected if CHF is
exposure and possible heartworm-associated present. DIAGNOSIS
respiratory disease [HARD]). In the United
States, exposure rate is approximately 12%. Etiology and Pathophysiology Diagnostic Overview
• Clinical signs associated with early infec- • Female mosquitoes serve as intermediate The diagnosis should be suspected when a
tion typically occur in late fall and early hosts after feeding on microfilaremic cat in an endemic geographic area demon-
winter. dogs. strates signs of respiratory dysfunction or
• Being an atypical host, cats have an inherent other systemic signs. Serum antibody and
ASSOCIATED DISORDERS resistance. antigen testing, thoracic radiography, and
• Aberrant migration of larvae is thought ○ Lower worm burdens (usually fewer than echocardiography each may contribute to
to be more common in cats than in dogs six, typically one to three) confirming the diagnosis, and the tests are
(neurologic, dermatologic, ophthalmic, and ○ Longer pre-patent period and shorter selected in sequence depending on availability
peripheral thromboembolic complications). worm patency than in dogs and cost.
• HARD: clinical (cough, wheeze, dyspnea) ○ Higher frequency of amicrofilaremia or
and pulmonary histopathologic findings low microfilaria counts than in dogs Differential Diagnosis
associated with death of immature fifth-stage ○ Shortened life span of adult heartworms • Cat with respiratory signs
larvae in the pulmonary vasculature, with or (2-3 years, although some new informa- ○ Bronchitis or asthma
without the presence of mature heartworms. tion suggests that worms may live up to ○ Lungworms (Aelurostrongylus abstrusus)
Pulmonary thromboembolism may be due 4 years) compared with dogs and other nematodes (Toxocara cati)
to dead worms (natural or pharmacologic • Disease severity is determined in part by ○ Paragonimus kellicotti infection
death) or intravascular thrombi formed in the number of adult heartworms and the ○ Pleural effusions (pyothorax, hydrothorax,
response to the infection, resulting in vascular host’s response to live and dead, immature chylothorax, or neoplastic)
occlusion, rarely in infarction, and sometimes and mature heartworms. ○ CHF due to cardiac disease
in acute respiratory death. ○ Pulmonary response is more severe in cats ○ Neoplasia
• Noncardiogenic pulmonary edema, often compared with dogs. Clinical signs can ○ Pneumonia (infectious or noninfectious)
fulminant (sometimes with pulmonary be seen before maturation of the larvae ○ Pneumothorax
thromboembolism), possibly represents acute (HARD)—or despite no worms reaching • Cat with neurologic signs (brain or spinal
respiratory distress syndrome (ARDS). This maturity (i.e., larvae are cleared)—and can cord)
may result acutely after adult worm death be observed as early as 3 months after ○ Various inflammatory, ischemic, neoplastic,
or deterioration. infection. or degenerative diseases of central nervous
• Eosinophilic pneumonitis with cough, • Response of the pulmonary arteries, system
wheezing, dyspnea pulmonary parenchyma, airways, and air • Cat with gastrointestinal (GI) signs, typically
• CHF (right-sided heart failure) is uncommon; spaces vomiting
signs include pleural effusion (hydrothorax ○ Eosinophilic infiltrates predominate. ○ Various systemic diseases such as neoplasia,
or chylothorax) and/or ascites. ○ Significant bronchointerstitial infiltrates hyperthyroidism, and renal failure or
• Wolbachia sp: as for dogs (p. 418) decrease functional pulmonary volume. primary GI disease

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