Heartworm

Question 1

How long is the life cycle of heartworm?

Answer 1

184-210 days (6-7 months)

Question 2

what stage of heartworm is transmitted from the mosquito to the dog?

Answer 2

L3

Question 3

where is heartworm maturation completed?

Answer 3

PA

Question 4

at what point does a HWI turn progress to HWD?

Answer 4

when worms get into the vasculature and cause damage to the pulmonary aa.

Question 5

within the pulmonary aa. what might heartworms induce?

Answer 5

inflammation, endothelial damage, myointimal proliferation, disruption of vascular integrity, fibrosis, and pulmonary hypertension

Question 6

what type of congestive heart failure might heartworm lead to?

Answer 6

R-sided!

structural changes to lumen of pulmonary aa. and vasoactive substance from worms > increased PVR > increased PAP > increased RV & RA pressure > tricuspid regurgitation

Question 7

how does heartworm cause thrombosis?

Answer 7

structural changes to lumen of pulmonary aa. and vasoactive substance from worms > increased PVR > increased afterload on RV > decreased CO > decreased pulmonary arterial flow

Question 8

what can lead to pulmonary parenchymal dz in dog with heartworm?

Answer 8

inflammatory immune response of host, increased vascular permeability, PTE, eosinophilic pneumonitis and granulomatosis

Question 9

what is wolbachia?

Answer 9

intracellular, gram-negative bacteria that lives in D. immitis

Question 10

what drug is used in heartworm treatment to reduce or eliminate wolbachia?

Answer 10

doxycycline

Question 11

mechanical obstruction (by worms) of blood flow in the R. side of the heart & vena cavae leading to hemolytic anemia and cardiogenic shock

Answer 11

caval syndrome

Question 12

T/F: cats more commonly have aberrant migration of heartworm (neuro, muscular, ocular, systemic aa.)

Answer 12

TRUE, cats are unnatural host

Question 13

what clinical signs might you see in a dog with heartworm dz?

Answer 13

exercise intolerance, wt loss, lethargy, cough, tachypnea, dyspnea, hemoptysis, R-CHF signs, syncope or collapse, hematuria (hemoglobinuria)

Question 14

what heart abnormalities might you find in a dog with heartworm dz upon physical exam?

Answer 14

split S2, murmur due to tricuspid regurg, gallop

Question 15

T/F: the test of choice in diagnosing HWD in dogs is an antibody test and cats is the an antigen test

Answer 15

FALSE, opposite

cats don’t often get adults (false - more common in antigen test)

Question 16

what does the antigen test detect in diagnosing HWD?

Answer 16

Ags in reproductive tract of adult female

Question 17

what are the four main treatments you should do for dog with HWD?

Answer 17

1) macrocyclic lactone preventatives
2) doxycycline
3) exercise restriction
4) adulticide therapy with melarsomine dihydrochloride

Question 18

what macrocyclic lactone preventative is contraindicated in microfilaremic dogs?

Answer 18

milbemycin (potent and can cause anaphylaxis)

Question 19

what stages of HW do macrocyclic lactone preventatives reduce or eliminate?

Answer 19

microfilaria, L3, and L4

Question 20

why is exercise restriction so important in treating HWD?

Answer 20

reduces risk of thromboembolic complications

Question 21

what protocol should you use when treating a dog with HWD and why?

Answer 21

3-dose (“split-dose”) protocol with melarsomine dihydrochloride

less dramatic worm death and therefore less risk of post-adulticidal complications

Question 22

why is the “slow-kill” method of macrocyclic lactones contraindicated?

Answer 22

takes too long! ongoing damage to pulmonary aa. and lungs

Question 23

prevention and treatment of adverse rxns to microfilaricides, penumonitis, pulmonary granulomas, PTE, and analgesia for melarsomine injections are all reasons to use what drug in a dog with HWD?

Answer 23

corticosteroids

Question 24

other than a corticosteroid what other drug might you consider giving a microfilaric dog before conducting microfilaricidal therapy?

Answer 24

diphenhydramine

Question 25

air bud’s owner let him play basketball even after you said he must be on exercise restriction. he now has a PTE and you’ve given supplemental oxygen and a corticosteroid. what drug would you give for his severe pulmonary hypertension?

Answer 25

sildenafil

Question 26

comet has R-CHF secondary to HWD…what drugs would you use for treatment?

Answer 26

furosemide, sildenafil and/or pimobendan, and an ACE inhibitor

Question 27

T/F: shadow has caval syndrome!! quick kill the worms!! grab the melarsomine and give him a hearty injection

Answer 27

FALSE, contraindicated in caval sydrome. you must do an emergency worm extraction from the jugular vein

Question 28

inflammatory & proliferative dz of pulmonary arteries, bronchioles, and pulmonary parenchyma in cats without mature infections

Answer 28

heartworm-associated respiratory dz (HARD)

Question 29

T/F: adult live heartworms are NOT susceptible to pulmonary intravascular macrophages (PIMs)

Answer 29

TRUE, only immature L5 and dead worms

Question 30

what would be the cause of acute signs in a cat with HWD?

Answer 30

dead worm embolization, anaphylaxis-like rxn, or aberrant migration

Question 31

T/F: a positive Ab test means sassy the cat has a HWI

Answer 31

FALSE, must do an Ag test

detects L4s

Question 32

what would cause a false negative test result in an Ag test done on a cat?

Answer 32

worms aren’t fully mature or 0-1 females present

Question 33

sassy has HARD, what drugs should you use to treat her?

Answer 33

corticosteroids (i.e. prednisolone or dexamethasone)

+/- bronchodilator (terbutaline)
+/- doxycycline (wolbachia)
+/- clopidogrel (PTE prevention)