Spiruroids - Heartworm Flashcards
Lifecycle of Canine Heartworm
Pathogenesis of heartworm
Presence of worm and Wolbachia (bacteria needed for survival) -> proliferative endarteritis (thickening) of pulmonary ateries -> decreased compliance ++
Thrombosis and thromboembolism (esp with dead parasites) -> pulmonary hypertension -> increased afterload of R ventricle -> R ventricular hypertrophy and dilation -> RSCHF +/- caval syndrome (worms migration to the heart and liver in the end stages)
Clinical signs caused by the immune response. Antigens also from Wolbachia
Pulmonary Arterial Disease?
Myointimal proliferation > villus proliferation of endothelium; inflammation; leakage
Caval Syndrome
Clinical signs
Heartworm diagnosis
- History - travelled recently? Heartworm prevention?
- Detection of mff in blood (won’t tell you which species)
- concentration methods (knotts test, filtration method)
What is an occult infection?
- 30% are occult
- no mff in the circulation
(all worms are the same sex, single worm infection, pre-patent infection or geriatric worms, ectopic infections, drug induced elimination (ivermectin, doxycycline), immunologically mediated elimination of mff)
Problems with diagnosis methods?
False neg due to occult infection
No indication of worm burden
Other filarial species in your area???
Further tests
- Antigen tests to adult female worms (at leats 3 females needed for consistent results)
- SNAP ELISA
- Sp (96-100%) and Se (90-96%)
- Beware - PPV and NPV when interpreting test in low prevalence area.
What does the inverted D mean?
enlarged R ventricle
Control of heart worm.
Drug efficacy on the age of parasite
Treament step 1: supportive care
A) strict rest up to 4 weeks post treatment (exercise makes RSCHF worse)
B) corticosteroids: prednisalone 0.5 mg/kg alternate days pre- and up to 1 month post adulticide
C) PLUS doxycycline @ 10 mg/kg for 3-4 weeks (Wolbachia)
Treatment Step 2: Prevent new infections and kill mff
Macrocytic lactones (monthly chew or injectible) start on day 0
- prevent new infection
- Kills circulating mff over 7-10 days old (beaware of anaphylaxis if too quick)
- over the longer term (4-12 month) kills juveniles and adults
Treatment Step 3: Kill Adults
Adulticide:
- Melarsomine by deep IM lumbar injection - kills worms >4mo
- (one injection followed at least by 1 month later by 2 injections of the same dose 24 hours apart)
- Monitor clinical improvement
- repeat antigen test in 6 months to confirm adulticide success.
Overall treatment timeline
How to deal with caval syndrome?
- surgical extraction of worms
Alternative regime “soft kill”
- if don’t have melarsomine use ML + doxycycline (10mg/kg, 1 month on, 2 months off) over 9 months-12 months to kill adult worms.
Problems with soft kill method?
Clinical signs may develop or worsen in the interim
Dont know when adults are dying
resistance?
Heartworm in cats prevalence
5-20% of that in dogs
Features of heartworm in cats
- most worms don’t mature
- 8 month PPP
- often no mff
- shortened adult survival (2-3 years)
Aberrant migration (e.g. CNS)
Clinical signs of heartworm in cats
HARD
Heartworm Associated Respiratory Disease
- due to larvae arriving
- pulmonary arteriole hypertrophy, pulmonary oedema, tachypnoea, cough, vomiting, weight loss
- usually a result from embolus of dead worm, not due to the presance of the worms themselves -> severe dyspnoea, haemoptysis, collapse, sudden death.
Pathophysiology of heartworm in cats
Diagnosin heartworm in cats
- antibody test - early as 8 weeks post-infection
- Antigen test if > 1 adult female
- Radiograph changes HARD
+/- bronchialviolar pattern
+/- enlargement of caudal lobar arteries
+/- adults on ultrasound
Treatment of cats with heartworm
Prednisolone
Surgery if worms visualised in ‘reachable’ area
DON’T use adulticides!
