Heartworm

What is the species of Heartworm?

What is the species of Heartworm?

Dirofilaria Immitis

What are the reservoir hosts for Heartworm?

Foxes and Coyotes

Which is the natural host and which is an atypical host: Cat & Dog?

Canine: Natural

Feline: Atypical

Where do the adult and larvae live?

Larvae: circulating blood, vascular urge, tissues

Adults: pulmonary outflow track of the heart

How is Heartworm transmitted?

Bite of Anopheles mosquito

What is Heartworm’s prepatent period?

6 months

How can you diagnose Heartworm?

• PCV (microfilarial Buffy coat)

• Direct Smear

• Modified Knotts (gold standard)

• ELISA (antigen/antibody)

What species does a modified knotts test differentiate between?

A. Recondition and D. Immitis

What are 3 preventions for Heartworm?

• Macrocytic Lactones

  • Ivermectin

  • Moxidectin

  • Milbemycin

How often are dogs tested?

Annually

How often are cats tested?

According to exposure and risk

• outdoor cats more risk than indoor cats

When can you start preventatives in puppies? What about older dogs?

• Puppies: under 6 months without a HW test

• Older than 6 months: need to be tested before preventative and then tested again in 6 months

What should you do if you miss a dose of the preventative?

Test immediately and again in 6 months, followed by yearly

What does the American Heartworm Society recommend for tests?

Antigen test (adults)

Microfiliaria Test (Larvae)

What is the antigen test?

Detects proteins made from female adult heartworms

• contains antibodies if antigen is present will bind and become positive

What should you do after getting a positive test?

1. Confirm with another type of test.

2. Imagine to assess heart

3. Stage the Patient (4 classes)

4. Restrict Exercise

5. Stabilize the patient / disease

6. Give Treatment

What are the four steps of treatment?

1. Pre-treatment testing

2. Treatment

3. Post-treatment rest

4. Post-treatment testing

Pre-treatment

• establishes ability to handle the treatment anf establish the stage of the disease

• Radiographs: heart/lung status

• BW: organ failure

Treatment

• prior to starting adulticide, patient given doxycycline and microfilariacide

• Patient given adulticide (Melarsomine)

Post Treatment Rest

• imperative dog rests

• Dead worms migrate through the lungs and eventually reabsorbed by the body

Post treatment Testing

• ELISA and microfiliaria test to test for absence of adults and microfilaria

Why are cats and collies sensitive to Ivermectin?

Don’t have protein on BBB that prevents the drug from crossing to the brain

What is the 3 injection procedure timeline?

Day 1: started on doxycycline and microfilariacide

Day 60: Melarsomine administered deep into sacral muscles

• P often kept overnight

• Strict rest begins

  • ± doxycycline

  • ± prednisone (inflammation and immune response)

Day 90: 2 doses of Melarsomine repeated 24 hours apart

Day 150: ivermectin (microfilaricide) is given & prevention started

What is Caval Syndrome?

• acute phase, severe form of HW

• Seen in dogs with heavy HW loads

• Fatal without surgical intervention

What causes Caval syndrome?

Migration of worms into the heart and worms obstruct the closure of the tricuspid valve

• lysing of RBC’s

• Failure of cardiac output

Clinical Signs of Caval Syndrome

• jugular distention with bounding pulse

• Tachycardia

• Hemoglobinuria

• Weak pulses

• pale MM, delayed CRT

• Hepatomegaly and or splenomegaly

Fluoroscopic Removal

• anesthetized patient and jug. Cath. Place in R. Jug.

• Fluoroscopy with a catheter with a snare is advanced to vena cava, right atrium, and left ventricle

• Snare catches and removes worms obstructing tricuspid valve

Surgical Cutdown

• incise the right jug and pull out visible worms

Why do we not see a lot of cats with HW?

• believed to be significantly under diagnosed

• Clinical signs not apparent

• Have more male only infections

HARD

Heartworm Associated Respiratory Disease

Antigen vs Antibody tests in cats

Antigen can result in false negative because you need females to produce the antigen levels and it takes 8 months for adult females to make antigens. ANtibody is more useful because it can detect male and female larvae as early as 2 months