Heartworm

Question 1

Where does canine dirofilaria immitis reside?

Answer 1

Pulmonary arteries and occasionally the right ventricle

Question 2

After the mosquito bites the dog, what happens?

Answer 2

L3, the infective stage, enter the wound and molt to L4 in SQ tissues between 3-12 days after infection. The l4 migrate through the tissues and molt to immature adult within 45-70 days post infection. L3 and L4 are not found in the circulatory system! Immature adults enter the circulation; microfilariae are deposited within 6-7 months (PPP).

Question 3

Does transplacental transmission in dogs occur?

Answer 3

Yes but the worms will not mature.

Question 4

What’s the main pathological sign in dogs?

Answer 4

Progressive pulmonary hypertension–>lung disease. Caval Syndrome can occur.

Question 5

What is an important bacteria in heartworm?

Answer 5

Wolbachia pipientis-symbiotic, Gram -, released in worm death, bacteria and endotoxns exacerbate lung injury-removal lessens lung pathology.

Question 6

What’s Caval Syndrome?

Answer 6

Acute disease caused by immature heartworms maturing at the same time and occurring in the right atrium, tricuspid, posterior vena cava. Sudden onset, rapidly fatal

Question 7

What do all commercial antigen tests detect?

Answer 7

Female uterine antigen, do not test dogs prior to 7 months old.

Question 8

How do you get false negative tests?

Answer 8

Low worm burden, immature females, male only infections, not allowing tests to warm to room temp, immune complexes binding Ag (can heat serum to avoid this)

Question 9

How do you get false positive tests?

Answer 9

well tests due to inadequate washing, cross reaction with other antigens such as Spirocerca lupi, test error, residual circulating antigens

Question 10

What’s the difference between these microfilariae and A. spp. ones?

Answer 10

These are OVER 270um and have an anterior tapered body

Question 11

What are occult infections?

Answer 11

Adults are present but no microfilariae. Prepatent, unisex, drug reduced, or immune mediated clearance

Question 12

What would you see on an echocardiogram?

Answer 12

Double line where worm is

Question 13

What are all heartworm preventives?

Answer 13

Macrocyclic lactones

Question 14

Give the drugs and dosages

Answer 14

Ivermectin, oral, 6ug/kg monthly; milbemycin oxime, oral, 0.5mg/kg monthly; moxidectin 0.17mg/kg six month injectable; moxidectin/imidacloprid 2.5mg/kg and 10mg/kg monthly topical; selamectin, topical, 6mg/kg monthly

Question 15

What two products provide a reach back and forward effect?

Answer 15

ProHeart and Advantage Multi

Question 16

What is the standard treatment for dogs?

Answer 16

Day 0-1: diagnose and verify, do a work up, administer doxy and prednisone if clinical signs; Day 30: preventive; Day 60: preventive, injection of melarsomine and prednisone for 4 weeks, exercise restriction; Day 90-91: preventive, 2 injections of melarsomine 24 hours apart, prednisone for 4 weeks, exercise restriction for 6-8 weeks; antigen test 6 months after 3rd melarsomine injection

Question 17

Slow kill therapy

Answer 17

monthly use of macrocyclic lactones can result in unpredictable worm death, antigen negative dogs may still actually be positive

Question 18

Is this disease zoonotic?

Answer 18

Rarely, may look like TB on an x-ray so need to do surgery

Question 19

Can cats get this?

Answer 19

Yes at a lower rate, PPP 7-8 months because cat is resistant

Question 20

Heartworm associated respiratory disease

Answer 20

Two stages. Stage 1: 3-4 months after infection, lung has intense inflammation and asthma-like symptoms, activation of PIM in lung leads to acute inflammatory reaction with eosinophilic and alveolar reactions (With stage 1 there may be no mature worms and still be life threatening!); stage 2: 1-3 years after infection, mature parasite and may be no clinical signs (downregulate PIM) but when worms die, the lung is inflamed and PIM leads to intense reaction->acute respiratory distress syndrome because of lung injury

Question 21

What are the two serological methods for feline heartworm?

Answer 21

Female uterine antigen and antibody against molting larvae; excellent because low worm burden, male only infections, symptomatic immune infections, immune complexes binding antigen

Question 22

How is antibody testing done in the cat?

Answer 22

Produced by cat in response to migration of L3/L4. Positive titers detected 1-3 months after infection. Monthly macrolide preventives can induce an antibody response even if the cat is actually negative. The cat has been exposed to the worms even if not currently infected if positive

Question 23

What is the treatment for cats?

Answer 23

DO NOT use melarsomine, it is toxic! Do mechanical removal and supportive care, signs are not good (prednisone for lung disease)

Question 24

What are the prevention doses for cats?

Answer 24

Selamectin, topical, 6-12mg/kg; moxidectin, topical, 1mg/kg (2.5x lower), ivermectin, oral, 24ug/kg (4x higher); milbemycin oxime, oral, 2mg/kg (4x higher)