Heartworm Flashcards
What is Heartworm?
Dirofilaria immitis
Round worm, lives in pulmonary arteries and RHS of heart
Mostly dogs, also cats and ferrets
Transmitted by mosquitos
What is the life cycle
After mating, females release L1 into the circulation
L1 ingested by moquitos during a blood meal
Matures in the mosquito, needs to be above 14 degrees
at 30 degrees takes 8d, at 18 takes a month to mature
L3 injected into connective tissue during blood meal
Mature to L5 whilst migrating through connective tissue
L5 move to the heart, take 3-6 months to mature and release L1
PPP 6m dogs, 8m cats
What is occult heartworm infection?
Adult stages present but no L1
Outline the pathogenesis of heartworm disease
Adult worms narrow vessesl - pulmonary hypertension
Arterial disease can lead to increased wall permeability, with periarterial oedema, interstitial and alveolar cellular infiltrate and can lead to irreversible fibrosis
PTE also possible
RHS CHF if migrate into the heart/ caudal vena cava as they cause tricuspid insufficiency
Haemolysis or haemoglobinaemia as RBCs burst going through the group of parasites
What is caval syndrome?
Combination of RHS CHF and IV haemolysis
Frequently also see DIC/ PTE
Why is immune mediated glomerular disease (presenting as a PLN) common in heart worm disease?
Unclear
What is typical of the clinical signs shown by heart worm dogs?
Appear slowly overtime
most obvious at exercise and sedentary patients may never show signs
May only present d/t an allergic reaction associated with worms, or when v v v high worm burden
What are the typical signs in dogs?
Cough most common Tachypnoea/ dyspnoea Exercise intolerance weight loss anorexia Syncope In severe cases may get haemoptysis RHS failure
What do you see on bloods?
Eosinophilia esp in early stages - on bloods and BAL
May see L1s on blood smear
What may you see on rads?
Bulge of pulmonary artery
Enlarged/ tortuous pulmonary arteries
RHS heart enlargement
Outline direct microscopic examination
Not overly sensitive by may see L1 moving around RBCs on a drop of blood
Filtration methods and the modified knots test may be more specific
Outline antigen tests
Detect specific proteins assocaited with the adult females reproductive tract
V sensitive and specific
Antigen levels undetectable by 8-12 weeks post tx
False -ves if immature worms, male only populations, or small worm burdens
What are the classes of infected patients and what is their px following tx with adulticide?
Class 1 - mild to no clinical sings - good px
Class 2 - mild to moderate clinical signs - may be good
Class 3 - severe clinical signs - guarded due to risk of PTE after tx
in cats, even mild infections have decent chance of PTE, so better to monitor rather than tx as many will resolve on their own
Tx severly infected cats as though they have asthma
How do you tx heartworm
Melarsomine - inject q24hr twice - only once in Class 3 patients d/t risks of PTE - give again in a month if stable
Kill L1s 4-6 weeks later with milbemycin oxime or ivermectin - may need to given 1-2mg/kg pred at same time to control anaphylactic
How do you minimise risks of PTE when treating?
AI dose preds
rest
