Feline heartworm disease

Question 1

What are the differentiating features of cats when compared to dogs

Answer 1

Cats are an atypical host (not the definitive host for Dirofilaria immitis

Infection rates are much lower in cats

Cats tend:
- to have fewer worms (typically less than 6)
- maturation of the worms takes longer
- the pre-patent period is prolonged (8 months)
- there is a shorter period of reproduction
- the worms don’t tend to live as long (2-3 years compared to 5-7 years in dogs)

Question 2

What is the cause of peracute and acute signs in heartworm disease

Answer 2

Peracute and acute signs are thought to be secondary to the death of adult worm and subsequent embolization, aberrant migration, or an anaphylactic reaction to the worms
- sudden death may be the first and only sign that the cat has heartworm disease

Question 3

What is the main cause of death in cats with heartworm disease

Answer 3

Many cats die of respiratory failure due to generalized pulmonary edema and acute respiratory distress syndrome

Question 4

What are the most frequent clinical signs associated with heartworm disease

Answer 4

The most common presentation is one of chronic disease:
- anorexia
- weight loss
- lethargy
- cough
- dyspnoea
- vomiting
- (very rarely, cats may show signs of right-sided CHF)

Question 5

How are explained the chronic respiratory signs

Answer 5

Most chronic respiratory signs are secondary to destruction of the fifth larval stage L5 within the pulmonary vasculature, triggering a widespread allergic response

Question 6

Explain why the Knott’s test is not useful as a screening test in cats for HWD

Answer 6

Because most cats do not have a circulating microfilaremia (L1)

Question 7

Explain why the ELISA antigen tests are frequently negative even in the face of a live worm burden

Answer 7

These tests rely on the detection of gravid female worm antigen, and an individual cat may be infected with only 1-2 immature or male worms and still have signs of disease

If positive, the test has nearly 100% specificty (sensitivity 80%)

Question 8

What is the most reliable radiographic finding in HWD

Answer 8

The most reliable radiographic finding is enlargement of the right caudal pulmonary artery
- may be present in only 50% of cases

Question 9

What are the main radiographic differential diagnoses for HWD

Answer 9

Lungworm

Allergic airway disease

Question 10

What is the treatment for HWD

Answer 10

Cats that have been diagnosed with HWD should be placed on:
- a monthly preventive (e.g., selamectin, moxidectin)
- prednisolonie (1-2 mg/kg, q12h, then tapered) is used to control the inflammatory response within the lungs

Question 11

Explain why adulticides and microfilaremic therapy are not used in cats

Answer 11

Thromboembolism of dead worms is potentially fatal
- thus, the use of adulticide is not recommended

Microfilaremic therapy is not necessary in cats as they are not considered a reservoir host