Page 235 - Small Animal Internal Medicine, 6th Edition

CHAPTER 10 Pulmonary Hypertension and Heartworm Disease 207

SURGICAL THERAPY maritime provinces of Canada. The natural definitive host
Caval syndrome occurs rarely in cats. Successful removal of of Angiostrongylus vasorum is the wild fox. Similar to diro-
VetBooks.ir adult worms through a jugular venotomy is possible, as in filariasis, domestic dogs can serve as a definitive host and
shed L 1 larvae in feces; worms can mature in experimen-
dogs. Prior echocardiographic confirmation of worm loca-
tion is important. A right jugular venotomy can be used to
requires a gastropod intermediate host (marine or fresh-
reach worms in the RA, vena cava, and possibly the RV with tally infected cats, but no larvae are produced. The life cycle
small alligator forceps, endoscopic grasping or basket water snail or slug). L 1 larvae are ingested by the gastro-
retrieval forceps, or another device. Worm removal via tho- pod host during feeding on fox or dog feces and undergo
racotomy and right atriotomy, ventriculotomy, or pulmo- two molting stages within the snail or slug to develop into
nary arteriotomy also has been done successfully. A infective L 3 larvae. Dogs become infected by eating either
potentially fatal anaphylactic reaction associated with worm the gastropod or a paratenic host (frog). Once ingested, L 3
breakage could occur during such procedures. Presurgical larvae penetrate through the intestinal mucosa and migrate
treatment with a glucocorticoid and antihistamine has been to abdominal lymph nodes. Immature worms then travel
suggested. via the portal circulation to the pulmonary arteries, where
they mature, mate, and produce eggs. Immature worms
MICROFILARICIDE THERAPY reach the pulmonary arteries by approximately 30 to 35
Microfilaricide therapy is rarely necessary because microfila- days postinfection. Eggs lodge and develop in pulmonary
remia is brief. The combination of monthly HW preventative capillaries; when L 1 larvae hatch, they break into airspaces
and doxycycline are sufficient to kill any microfilaria present. and are coughed up and swallowed to pass in the feces of
infected hosts. The overall prepatent period for A. vasorum
HEARTWORM PREVENTION is approximately 5 to 8 weeks. Life span of the adult worms
HW prophylaxis is recommended for cats in endemic areas, is at least 2 years and can last the lifetime of the canine
including those living “indoors” only. Monthly preventative host, leading to lifelong intermittent shedding of larvae
should be initiated 1 month before the beginning of regional in feces.
HW transmission season and continued until at least 1 Pathophysiologic consequences of angiostrongylosis are
month after the season has ended. However, year-round pre- similar to HWD in dogs. Worms cause an inflammatory
vention has advantages, including improved compliance, response in the pulmonary arteries that can cause pneu-
retroactive activity (“reachback”) in case of missed doses, monitis, interstitial pneumonia, or pulmonary granulomato-
and activity against GI parasites. Oral HW prevention prod- sis. Pulmonary vascular lesions include villous arteritis and
ucts for cats include ivermectin (Heartgard for Cats) and intimal proliferation. Incidence of PTE and PAH appear to
milbemycin oxime (Interceptor Flavor Tabs for Cats); topical be less than in canine HWD, possibly due to recruitment
options include selamectin (Revolution) and a moxidectin/ of pulmonary arteriovenous shunts. Only approximately
imidacloprid combination (Advantage Multi for Cats). Sela- 15% of dogs diagnosed with A. vasorum in the United
mectin is used at the same dose as for dogs (6 mg/kg, topi- Kingdom have moderate to severe PAH; right-sided CHF
cally); it is also useful for controlling fleas and ear mites, as is therefore a rare complication. Coagulopathies such as
well as hookworm and roundworm infections in cats. Iver- thrombocytopenia and DIC can occur, and hemorrhage is
mectin is administered orally at 24 µg/kg monthly (four a relatively frequent complication compared with HWD.
times the dose used in dogs). The minimum recommended Aberrant migration of adult worms has been reported,
dose for oral milbemycin is 2 mg/kg (about twice the dose including to sites such as the eye, left heart, and femoral
used in dogs). Moxidectin is used at 1 mg/kg, applied topi- artery. Aberrant migration of L 1 larvae is common, includ-
cally. All these agents are safe in kittens 6 weeks or older, and ing to the brain, spinal cord, eye, kidney, liver, or other
all preventative agents are safe for use in seropositive cats. abdominal organs.
Serologic testing before preventive use can be useful for pur- Clinical presentation of dogs with angiostrongylosis is
poses of identifying local HW prevalence, as well as indi- variable and based on disease severity but generally mimics
vidual cat risk for HARD or adult HWD. However, the HWD. Dogs could present for cough, dyspnea, anorexia,
usefulness of serologic testing for individual cats before ini- exercise intolerance, or syncope. Sudden death has been
tiating monthly preventative is less than dogs. reported. Coagulopathic (hemorrhagic) presentations are
common as well, including mucosal or subcutaneous hemor-
rhage, melena, or hemoptysis. Common clinicopathologic
ANGIOSTRONGYLOSIS findings are similar to those in dogs with HWD, and include
eosinophilia, neutrophilia, thrombocytopenia, mild anemia,
Infection with metastrongylid nematode Angiostrongylus and hyperglobulinemia. Prothrombin time (PT) and acti-
vasorum in dogs, also known as the “French heartworm,” vated partial thromboplastin time (APTT) are often pro-
can cause pulmonary vascular disease similar to dirofila- longed. Thoracic radiographs typically reveal a patchy
riasis. Angiostrongylosis is regionally endemic in parts of alveolar-interstitial pattern in peripheral lung areas and,
Western and Northern Europe and the United Kingdom, occasionally, mild pleural effusion; pulmonary vascular
as well as in Turkey, Brazil, Colombia, Uganda, and the lesions (enlarged and tortuous pulmonary arteries) are less