Heartworm disease Flashcards
The heartworm parasite
Dirofilaria immitis
What are the different stages of Dirofilaria immitis?
Laraval stages L1, L2, L3,L4
Adult
Is Dirofilaria immitis zoonotic?
Yes but there are relatively few reported cases in humans
L1, microfilaria
Offspring of adult heartworms
In the bloodstream of hosts
L1, L2, Infective L3
Matures in the mosquito until L3 enters the new host during feeding
L3, L4
migrates to the heart
Where do the adult heartworms live?
The right side of the heart and the pulmonary arteries
20-25 cm long
What is the intermediate host for Dirofilaria immitis?
Mosquito
What is the predilection site of Dirofilaria immitis?
Pulmonary arteries and right ventricle
What are the clinical signs of heartworm disease?
Coughing
Exercise intolerance
Syncope
Ascites from right-sided heart failure
What are the two types of tests used to diagnose heartworm disease?
Microfilarial tests
ELISA or RIM
Microfilaria Tests
Detects circulating mircofilaria
Uses whole blood
What tests does the microfilaria include?
Blood smears, PCV, modified Knotts, DIFIL test
Direct Blood Smear
Blood examined directly for microfilaria
What are the advantages of a direct blood smear?
Inexpensive, simple to perform
What are the disadvantages of a direct blood smear?
Not sensitive
Only 1 drop of blood is checked
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
Modified Knott’s test
Concentration method to look for microfilaria
What is the advantage of the modified Knotts test?
A larger amount of blood is examined compared to direct smear
What is a modified Knott’s test used for?
To distinguish Dirofilaria from non-pathogenic Acanthocheilonema reconditum
What are the most differentiating characteristics between Dirofilaria and Acanthocheilonema reconditum?
Body width, body length, and shape of the cranial end
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
Elisa or RIM tests
Detects antigen released by adult female or antibody produced by a host
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?
No
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
