Exam I - Dirofilaria immitis

Question 1

What is the common name for Dirofilaria immitis?

Answer 1

heartworm

Question 2

To which taxonomic superfamily does Dirofilaria immitis belong?

Answer 2

Filarioidea

Question 3

What is/are the intermediate host(s) for Dirofilaria immitis?

Answer 3

mosquitos

Question 4

What is/are the final host(s) for Dirofilaria immitis?

Answer 4

Dogs (definitive) and cats

Question 5

Describe the life cycle for Dirofilaria immitis.

Answer 5

• Adult females release microfilariae (L₁) directly into the blood stream where they can circulate for up to 3 yr or be taken up by female mosquitoes during feeding.
• In these intermediate hosts the L₁ develop to L₃ which are found in the salivary glands.
• The L₃ are the infective stage and are inoculated (up to 12) into dogs when the mosquito feeds again.
• Within a few days the L₃ molt to L₄ at the inoculation site.
• The L₄ migrate through the subcutaneous tissues and fat of the abdomen and thorax for 2 - 3 mo before molting to become L5 (adults which are not sexually mature; 1-2 cm in length) which enter a vein and are carried in the blood to the distal parts of the caudal pulmonary arteries.
• Here they develop into sexually mature adults in 2–3 mo and begin releasing microfilariae into the blood.
• The prepatent period is 6-9 mo.
• Adults survive for several years, and can be patent for 5-7 yr in dogs.

Question 6

Dirofilaria immitis microfilariae represent which larval stage?

Answer 6

L₁

Question 7

Which larval stage of Dirofilaria immitis is infective?

Answer 7

L₃

Question 8

What is the PPP for Dirofilaria immitis?

Answer 8

PPP is 6 - 9 months!

Question 9

How long can Dirofilaria immitis be patent in dogs?

Answer 9

5-7 years

Question 10

What is/are the site(s) of infection for Dirofilaria immitis?

Answer 10

Adult heartworms are mainly found in the distal parts of the _pulmonary arteries of the caudal lung lobes. _

(When large numbers of nematodes are present (e.g., > 50 in a 25 kg dog) they might also be found in the right heart and the caudal vena cava.)

Question 11

Describe the pathogenesis associated with Dirofilaria immitis in dogs.

Answer 11

• Endothelium is destroyed
• fluid leakage, thrombus formation
• Tortuous arteries
• Increased resistance
• Post-caval syndrome

Question 12

Recent studies have indicated that which intracellular bacteria harbored by D. immitis may contribute to the pathogenesis of heartworm disease?

Answer 12

Wolbachia spp

Question 13

Which laboratory test would result in a definitive diagnosis of Dirofilaria immitis about 6-9 months post-infection?

Answer 13

Microfilaria tests

Question 14

Which laboratory test for Dirofilaria immitis is considered most effective and most accurate?

Answer 14

Antigen tests

Antigen tests are highly specific and false positive findings are rare. The tests are also fairly sensitive (80% plus).

Question 15

True or False:

Prevention of Dirofilaria immitis is much safer and more economical than treatment

Answer 15

True.

Question 16

Macrocylcic Lactones are effective against which larval stages of Dirofilaria immitis?

Answer 16

MCLs effective against L₃ and early L₄

Larvae acquired the previous month are killed within a day of dosing. Problems occur if preventive missed. This accounts for prevention “failures” in practice

Question 17

Can cats get heartworm?

Answer 17

Yes.

Question 18

In a feline infected with Dirofilaria immitis, in which organ do we observe the greatest pathology?

Answer 18

Lungs

Question 19

Describe the approved treatment methods for Dirofilaria immitis in cats

Answer 19

There aren’t any