Heartworm in Dogs & Cats

Dirofilaria Immitis: Common Name, Definitive Host, Intermediate Host, Location, PPP (dog & cat)

Common Name: Heartworm

Definitive Host: dog, cat (atypical), coyotes, wolves, ferrest, grey seals, etc

Intermediate Host: mosquito

Location: Pulmonary Arteries (adults) - RH = heavy infection

PPP: 6-7 months (dog) & 7-8 months (cat)

What is the infective stage?

L3 

How long do microfilaria live in vascular system?

1-2 years

What happens when a mosquito with L3 bite a new host?

1. L3 migrate from salivary glands to subcutaneous tissue and molt to L4 (3-4 days)

2. L4 travel through SQ or muscle to thorax and molt to immature adult (2-3 months)

3. Immature adults enter circulation and are swept to pulmonary arteries

4. Mature and mate

How long do adults live in the dog?

5-7 years

What is the diagnostic stage?

Female worm Ag and microfilaria

Caval Syndrome

heavy infection where large mass of heartworms situated in RV, RA, and vena cava which can lead to sudden death due to cardiac failure and hepatic insufficiency

Wolbachia spp.

• symbiotic gram negative intracellular bacteria that is in ALL D. immitis

• released in large numbers at death of worm and during microfilaria production

  • makes lung injury worse

What determines how rapidly you see clinical signs?

number of worms, duration of infection, size of animal, exercise level of animal

True or False: Activity level is more important than the number of worms in regards to the severity of the disease.

TRUE

Diagnosis of D. Immitis

• detecting antigen made by female worms

  • D. immitis female uterine antigen (Ag)

• recovery of microfilariae

• Clinical signs

What can cause false negative antigen tests?

• low worm burden

• immature females

• male only infections

• human error

• Immune complexes binding (shelter animals)

What is the most common cause of false positive antigen tests?

residual circulating antigen

• can remain positive for up to 4 moonths following elimination of adult D. immitis

Knott’s Test

centrifugal technique used to concentrate microfilaria in the blood

What worm looks similar to D. immitis but is not pathogenic?

Acanthocheilonema reconditum

How do worms appear on echo?

double parallel lines in the main pulmonary artery

How is the preventative effect of HW prevention achieved?

killing L3 and L4 in SQ tissue depsoited within the last 30 days so they cannot mature

Treatment Protocol

Day 0: administer HW preventive & observe for anaphylaxis, admin doxy for 28 consecutive days, restrict activity

Day 30: finish doxy, keep on preventative

Day 31-59: wait

Day 60: 1st melarsomine injection (IM)

Day 90: 2nd melarsomine injection (IM)

Day 91: 3rd Melarsomine injection (IM)

Day 120: test for microfilaria (if + treat with microfilaricide and retest 2-4weeks)

Day 365: resume annual HW screening (if Ag +, doxy 28 days and retreat with 2 doses)

Where is melarsomine given?

between l3 and L5 ONLY (epaxial muscles)T

True or False: After sx removal of worms in caval syndrome, you do not need to use the three course melarsomine

FALSE

Why is slow kill not preferred?

Resistance likely to occur bc ur using macrolytic lactones longterm

HARD

Heartworm associated respiratory disease (in cats)

True or False: Single Sex infections are more common in dogs than cats.

FALSE. Cats commonly get male only infections

True or False: abberant migrations are more common in cats

TRUE

What is a diagnostic for cats that works?

Positive Ab test (antibody) & echo & tracheal wash (eosinophils)

Treatment of D. Immitis in CATS

NO MELARSOMINE

• surgery and supportive care is best

What kind of lesions are left in the lungs on radiograph?

Coin lesion