Lecture 1 Flashcards
What is dirofilaria immitis?
Parasitic roundworm spread through mosquito bites
Describe the heartworm life cycle
- A HW positive dog is bitten by a mosquito. The mosquito picks up the microfilaria (L1).
- The L1 larva mature through L2 and L3 in the mosquito.
- The mosquito bites a dog and deposits L3 larva onto the skin which enter the body through the puncture wound.
- The L3 larve mature through L4 and L5 and migrate through tissues to reach lungs.
- L5 penetrate blood vessels and enter the pulmonary arteries.
- Adults in the pulmonary arteries mate and produce L1 microfilaria which can be picked up by another mosquito.
What are the pulmonary vascular responses to the heartworms?
Endothelial irritation from direct contact
Inflammatory mediators will be released
Ag-Ab complexes will be formed
Pulmonary arteries will become dilated and blunted
What are the pulmonary parenchymal responses to the heartworms?
Local inflammation
Pulmonary fibrosis
Thromboembolism of dead worms
How do you diagnose heartworms in dogs?
Blood tests- microfilarial, antigen, and antibody tests
Thoracic radiographs
ECG- maybe
What is the most common test in dogs?
Antigen test (snap 4Dx test)
How long does it take for the life cycle to be completed?
6-7 months
What does the anitgen test detect?
Mature, gravid females only
When should you perform an antigen test?
Before staring prophylaxis (unless the dog is less than 6 months old)
If they haven’t had prophylaxis/they’ve had inadequate prophylaxis
Annually in case of errors in owner compliance or dog being sneaky and spitting pill out
What worm might you see on a blood smear that is NOT dirofilaria immitis?
When would you suspect this worm?
Acanthocheilonema Reconditum- need to send to a parasitologist to confirm
Would suspect this if you have a negative antigen test but see “microfilaria” on blood smear
What are the advantages of testing for microfilaria in the blood?
It validates a (+) antigen test
It identifies a patient as a reservoir of infection
Alerts you to the possibility of a reaction when you using a microfilaricide
What is an occult infestation?
When would you have an occult infestation?
Worm infestation without microfilaria
Would have if
- Only have L5 worms and younger
- Immune destruction of microfilaria (cats)
- Macrocyclic lactone administration post infection
If you see a puppy less than 6 months old with microfilaria, what does that mean?
Maternal transmission of L1 and HW infestation is not present
How do most dogs present with HW?
Asymptomatic
What are some symptoms a dog with HW may have
Cough
Exercise intolerance
Lethargy
Caval syndrome
What is caval syndrome?
What does it result in?
When worms become entwined in the tricuspid apparatus
Results in tricuspid regurgitation, volume overloaded right heart resulting in right sided CHF, volume underloaded left heart resulting in decreased CO and shock, IV hemolysis, hemoglobinemia and hemoglobinuria
What are some clinical signs of caval syndrome?
Sudden onset of severe lethargy Right sided systolic heart murmur Dyspnea Pale mm Hemoglobinemia/uria Jugular pulsations Shock Might have ascites/liver enlargement
When diagnosing heartworms, what might you see on thoracic radiographs?
May be normal
May have enlarged, tortuous pulmonary arteries
MPA bulge
Interstitial/alveolar patterns
Right sided cardiomegaly (reverse D)
ECG
Not necessary of work-up of HW
Not efficient method of diagnosis but can confirm caval syndrome
Class 1 HW
Clinical signs:none/ occasional cough
Exam: normal
Rads: normal
Class 2 HW
Clinical signs: occasional cough, mild to moderate exercise intolerance
Exam: increased lung sounds, fair general condition
Rads: mild PA enlargement; mixed interstitial/alveolar patterns
Class 3 HW
Clinical signs: persistent cough, increased respiratory effort, moderate to severe exercise intolerance, weight loss
Exam: tachypnea, dyspnea, split S2, gallop, increased lung sounds
Rads: moderate to severe PA enlargment, RV enlargement, diffuse, severe pulmonary lesions
Class 4 HW
Caval syndrome
What is the only FDA approved adulticide
Melarsomine (Immiticide)
What is fast kill?
Previously recommended for class 1-2 dogs, but no longer recommended because it only kills 90% of worms as opposed to 98%
What are some side effects of melarsomine?
Pain/inflammation at injection site- can treat with NSAIDS
Allergic reaction- All dogs should be treated with benadryl
Pulmonary inflammation/edema
Mild cough/lethargy/fever
Pulmonary thromboembolism
Why give doxycycline for one month before treating heartworms?
Kills wolbachia- an intracellular symbiotic bacteria with D. Immitis
This suppresses microfilaremia
Why give macrocyclic lactones for two months prior to adulticide?
It eliminates the susceptibility gap caused by neither immiticide nor macrocyclic lactones not killing late L4-early L5
Which macrocyclic lactone kills microfilaria the slowest?
Heartguard does of ivermectin
What other medications might you give prior to adulticide therapy
Steroids- if clinical signs warrant
Antihistamines- if giving MLs and microfilaria +
Aspirin- NOT INDICATED
What is the major post adulticide consequence we worry about?
Pulmonary thromboembolism (can’t see on radiographs)
When is surgical extraction of the worms indicated?ca
Life threatening caval syndrome
What is the controversy surrounding long term macrocyclic lactones in HW positive dogs with no adulticide?
Can lead to resistant strains
When should a puppy be started on prevention
No later than 8 weeks old
What HW preventions are available
All are macrocyclic lactones
Ivermectin (heartguard)
Milbemycin (Sentinel, Trifexis)
Moxidectin (Proheart, advantage multi)
Selamectin (revolution)
Can you use cattle ivermectin to prevent HW in dogs?
Yes, but it is off label and must be careful about dosing. DON’T use in MDR1 gene deficient dogs
