Heartworm Disease in Dogs and Cats

Question 1

What causes heartworm disease?

Answer 1

Dirofilaria immitis

Question 2

Where does adult Dirofilaria immitis reside within the dog or cat? What does this result in?

Answer 2

pulmonary artery and RV

RV hypertrophy

Question 3

How is Dirofilaria immitis transmitted? How does parasite burden differ in dogs and cats?

Answer 3

L3 larvae are transmitted through mosquito bites

dogs develop a higher burden

Question 4

What additional pathogen has been associated with Dirofilariasis?

Answer 4

the bacteria, Wohlbachia

Question 5

How does heartworm disease present in dogs?

Answer 5

right heart failure –> exercise intolerance, cough, dyspnea, ascites

Question 6

What are the 2 major presentations of heartworm disease in cats?

Answer 6

1. ACUTE (caused by worms dying and resulting in embolism/inflammation) - salivation, tachycardia, shock, hemoptysis, neurologic signs, acute death
2. CHRONIC - heartworm-associated respiratory disease (HARD) = asthma (coughing, wheezing), dyspnea, exercise intolerance, vomiting, anorexia, weight loss

Question 7

What is the best diagnostic for heartworm disease in dogs? What are some other options?

Answer 7

antigen test - detects Ag from adult female worms

• modified Knott’s test - detects microfilaria
• right-sided cardiac enlargement + enlarged pulmonary arteries on thoracic radiographs (reverse D)
• proteinuria
• eosinophilia

Question 8

What are 3 options for diagnosis of heartworm disease in cats?

Answer 8

1. heartworm antibody test - indicates exposure
2. thoracic radiographs
3. echocardiograph - appear as “double lined echodensity”

Question 9

What are 3 options for treating heartworm disease in dogs? What are other historical treatments?

Answer 9

1. Melarsomine - split protocol, first injection followed by 2 (24 hours apart) within 4-6 weeks
2. Doxycycline, Azithromycin, or Rifampin for Wohlbachia
3. monthly preventative while waiting for adults to die (not recommended)

Thiacetarsamide, Levamisole

Question 10

What side effect can be seen with using Melarsomine in cases of heartworm disease?

Answer 10

thromboembolic disease –> confine the animal!

Question 11

How is heartworm disease treated in cats?

Answer 11

treat symptoms + add preventatives

• bronchodilators
• corticosteroids
• wait until worms die (2-3 years in cats!)

Question 12

What are the 4 most common and effective preventions used for heartworm disease?

Answer 12

1. Ivermectin (Heartgard) - oral
2. Milbemycin (Sentinel) - oral
3. Selamectin (Revolution) - topical
4. Moxidectin and Imidacloprid (Advantage Multi)