Heartworm disease Flashcards by Danielle Stone

The heartworm parasite

Dirofilaria immitis

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What are the different stages of Dirofilaria immitis?

Laraval stages L1, L2, L3,L4

Adult

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Is Dirofilaria immitis zoonotic?

Yes but there are relatively few reported cases in humans

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L1, microfilaria

Offspring of adult heartworms

In the bloodstream of hosts

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L1, L2, Infective L3

Matures in the mosquito until L3 enters the new host during feeding

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L3, L4

migrates to the heart

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Where do the adult heartworms live?

The right side of the heart and the pulmonary arteries

20-25 cm long

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What is the intermediate host for Dirofilaria immitis?

Mosquito

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What is the predilection site of Dirofilaria immitis?

Pulmonary arteries and right ventricle

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What are the clinical signs of heartworm disease?

Coughing
Exercise intolerance
Syncope
Ascites from right-sided heart failure

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What are the two types of tests used to diagnose heartworm disease?

Microfilarial tests

ELISA or RIM

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Microfilaria Tests

Detects circulating mircofilaria

Uses whole blood

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What tests does the microfilaria include?

Blood smears, PCV, modified Knotts, DIFIL test

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Direct Blood Smear

Blood examined directly for microfilaria

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What are the advantages of a direct blood smear?

Inexpensive, simple to perform

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What are the disadvantages of a direct blood smear?

Not sensitive

Only 1 drop of blood is checked

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Buffy coat/PCV method

tape the tube to a slide and focus on the buffy coat for movement
Break the tube at the buffy coat and make a smear

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Modified Knott’s test

Concentration method to look for microfilaria

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What is the advantage of the modified Knotts test?

A larger amount of blood is examined compared to direct smear

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What is a modified Knott’s test used for?

To distinguish Dirofilaria from non-pathogenic Acanthocheilonema reconditum

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What are the most differentiating characteristics between Dirofilaria and Acanthocheilonema reconditum?

Body width, body length, and shape of the cranial end

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How do you perform the Modified Knott’s Test?

1 mL blood from LTT to 10mL formalin to lyse RBCs
Centrifuge for 2 minute
Discard supernatant 
Stain sediment with NMB
Pipette, coverslip, examine on 40x

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Elisa or RIM tests

Detects antigen released by adult female or antibody produced by a host

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What does an ELISA or RIM test use?

Whole blood, serum, or plasma

What else is an ELISA or RIM test called?

An occult test

What are Immunologic/Molecular Diagnostic Tests

Tests that identify antigen and/or antibody to specific parasite

What do the majority of immunologic/molecular diagnostic tests use?

Enzyme-linked immunosorbent assay (ELISA) principle

What are the advantages of an ELISA test?

Highly accurate and precise Can detect occult infections Rapid and easy to perform

What do some other Immunologic/Molecular diagnostic tests use?

Rapid Immunomigration (RIM)

What are the advantages of running a RIM?

Do not require refrigeration and no diluents

Heartworm antigen testing

Blood test to detect tiny amounts of protein from Dirofilaria sp. female worms

What labs perform the Heartworm antigen test?

IDEXX snap test | Heska

What are the advantages of running the Heartworm antigen testing?

Quick test Can detect very low worm burdens (as low as 3 female worms) Occult infections

Antibody Testing

Blood test to detect host's immune reaction to the adult worms Both male and female

What are the advantages of antibody testing?

Quick test Measures the host response to the presence of as few as 1-2 worms Can detect infection sooner than antigen testing Useful for feline cases

What are the disadvantages of antibody testing?

May not be available at all clinics If the heartworms are dead, the test may still be positive Does not distinguish between previous infection and current infection

Prepatency period of heartworms?

6 to 7 months

Heartworm guidelines in Hawaii

Year-round prevention recommended Annual heartworm testing recommended Testing on dogs greater than 6 months of age prior to starting prevention

Heartworm guidelines on the mainland

Prevention recommendations may vary | American Heartworm Society recommends year-round prevention and annual testing of all

What is the purpose of heartworm prevention

Prevents larval stage (L3 and L4)

What is the overall effect of heartworm prevention?

Stops the development of parasite

Can pets still get infected while on prevention?

Yes but larvae do not develop past 3rd larval stage

Oral heartworm medication

Heartgard, Trifexis, Sentinel

Topical heartworm medication

Revolution

What does heartworm treatment do?

Eliminates heartworm in a 2-step process | Must get rid of the adult worms and microfilaria separately

How does heartworm treatment kill adults?

2-3 injections to kill adult heartworms | Usually deep lumbar IM injections

How does heartworm treatment kill microfilariae?

With a preventative

What is Immiticide?

Arsenic- based drug

In what organs does immiticide have serious side effects?

Kidney and liver

What happens to the pet as the adult heartworm dies and breaks apart?

They cause a reaction in the lungs | An acute respiratory problems

What is required for the pet during the treatment?

Strict rest for 4 weeks Especially for the first 7-10 days Need a cage or kennel confinement for active dogs

What does a heartworm infection cause in cats?

Respiratory symptoms | can mimic asthma

What are the symptoms of heartworm disease in cats?

They may not have any symptoms | just cause sudden death

Is there heartworm treatment available for cats?

Why do you give indoor cats monthly heartworm preventative?

Because mosquitos intermediate hosts

DIFIL Testing

- uses lots of blood | - finds microfilaria

What do you need for a DIFIL Test?

Blood from the LTT tube | The solution that comes with the kit

How do you perform a DIFIL Test?

``` Add the filter on to the syringe Squirt the blood through the filter Microfilaria will stick to the filter Put the filter with a drop of stain onto a glass slide Examine it under the microscope ```