Lecture 11 2/16/24

Question 1

What are the general characteristics of Dirofilaria immitis?

Answer 1

-IH is mosquitoes
-DH is dogs/wild canidae, marine mammals, ferrets, cats
-males 12-22 cm
-females 25-31 cm
-mf 300 x 7 um
-PPP 6 months

Question 2

What are the characteristics of the Dirofilaria immitis life cycle?

Answer 2

-juvenile worm matures to adult over 3 month period
-microfilaria produced by young adults 6 months post-infection
-lifespan of 5 to 7 years for adults; 2 years for mf
-average infection of 14 worms

Question 3

What clinical signs are associated with heartworm infection?

Answer 3

-potentially asymptomatic
-cough
-dyspnea
-exercise intolerance
-weight loss
-ascites
-anemia
-eosinophilia
-thrombocytopenia
-glomerulonephritis
-proteinuria

Question 4

What causes the clinical signs associated with heartworm?

Answer 4

-pulmonary arterial disease with inflammation and arteritis
-pulmonary thromboemboli
-pulmonary hypertension
-prolonged severe pulmonary hypertension/potential right heart failure

Question 5

What is the gold standard for heartworm diagnosis?

Answer 5

-Knott’s/filter test
-antigen test

Question 6

What is important about the timing of heartworm testing?

Answer 6

-earliest possible detection of heartworm antigen is 5 months
-low worm burden and and preventatives can delay antigen detection

Question 7

What can lead to a dog being AG positive and Knott’s negative?

Answer 7

-5 month old worms
-all female worms
-immunological occult
-prophylaxis induced
-few mf present

Question 8

What can lead to a dog being Ag negative and mf positive?

Answer 8

-dead adults with mf circulating
-antibody sequestration/antigen-antibody complexes

Question 9

How can radiographs be used to diagnose heartworm?

Answer 9

-right-sided heart enlargement
-“reverse D shape”

Question 10

Why is monthly heartworm preventative considered to be retroactive?

Answer 10

the monthly dose kills what has accrued in the animal in the past month

Question 11

Why does transplacental transmission of heartworm not lead to adult worms in puppies?

Answer 11

the microfilaria must go through the mosquito IH to become an adult

Question 12

Which drug is used to treat adult heartworms?

Answer 12

melarsomine dihydrochloride

Question 13

Why is it important to separate out heartworm treatment into multiple doses?

Answer 13

killing fewer worms per treatment reduces the cumulative impact of worm emboli

Question 14

What should be done during month one of heartworm treatment?

Answer 14

-start monthly heartworm prev.
-prescribe doxycycline to kill Wolbachia
-prescribe pred. to reduce symptoms
-begin exercise restriction

Question 15

How does Wolbachia contribute to heartworm pathogenesis?

Answer 15

-surface proteins contribute to pulmonary/renal inflammation
-bacteria releases endotoxin

Question 16

What should be done during month two of heartworm treatment?

Answer 16

give second dose of heartworm prev.

Question 17

What should be done during month three of heartworm treatment?

Answer 17

-give third dose of heartworm prev.
-give first melarsomine inj.
-prescribe pred. to control symptoms
-further decrease activity level

Question 18

Why is exercise restriction important during heartworm treatment?

Answer 18

aids in minimizing pulmonary emboli and thrombosis

Question 19

What should be done during month four of heartworm treatment?

Answer 19

-give fourth dose of heartworm prev.
-give second and third melarsomine inj.
-prescribe pred. to control symptoms
-continue exercise restriction for 6-8 weeks post last injection

Question 20

What should be done after completing heartworm treatment?

Answer 20

performing both an antigen test and a Knott’s test 6 months after completing treatment

Question 21

What are the main treatment principles that apply to heartworm?

Answer 21

-three melarsomine dose protocol kills 98% of adults (100% clearance)
-thromboembolism WILL occur - exercise restriction important
-prednisone is treatment of choice for inflammation associated with embolism
-doxycycline reduces Wolbachia

Question 22

What are the characteristics of caval syndrome?

Answer 22

-occurs when animal has so many worms that they enter right atrium and vena cavae
-life threatening
-requires immediate surgery
-adult chemotherapy only after animal is stable post-op

Question 23

What are the characteristics of Acanthocheilonema?

Answer 23

-IH is fleas/lice/ticks
-DH is dogs/cats/primates/raccoons/marine mammals
-males 9-17 mm
-females 20-32 mm
-mf 270 x 5 um
-PPP 2 months

Question 24

How do dogs and cats differ in terms of worm burden?

Answer 24

when exposed to 100 L3:
-dogs will develop approx. 75 adult worms
-cats will develop approx. 5-10 adult worms

Question 25

What are the characteristics of Dirofilaria in cats?

Answer 25

-adults have shorter lifespans
-often no microfilaria
-ectopic infection more common
-often in the lungs instead of heart

Question 26

What clinical signs are associated with heartworm in cats?

Answer 26

-dyspnea
-coughing
-vomiting
-neurologic signs
-sudden death
-may be asymptomatic

Question 27

Why is it more likely to get a false neg. heartworm test in cats?

Answer 27

-antigen tests only detect antigens from female worms; cats typically only have male worms
-cats do not typically have microfilaria for detection via Knott’s test

Question 28

When is disease most likely to occur in cats with heartworm?

Answer 28

-immature worms enter pulmonary arteries
-worms die within pulmonary arteries

Question 29

How does heartworm treatment differ between dogs and cats?

Answer 29

-no recommended adulticidal treatment in cats
-focus instead on relieving clinical signs in cats
-provide supportive care and prophylaxis