Dirofilaria immitis Homepage
Common name: Canine heartworm
Genus : Dirofilaria
The adult worms measure 15 cm (male) to 30 cm (female).
Adult worms: male and female (left), worms in situ (right)
The mosquito ingests a microfilaria when feeding on an infected dog. The microfilaria develops into an infective larva in about 14 days. When the mosquito again feeds on a dog the infective third stage-larva is injected into the skin. The third stage-larva molts to the fourth stage within 48 hours. The fourth stage-larva migrates through the dog's tissues, eventually reaching the pulmonary artery where it matures to the adult stage.. The female worm lays microfilariae into the blood. The prepatent period is about 6 months.
The only stage of the parasite which can be recovered for diagnosis is the microfilaria (a free swimming embryo found in the blood). However, microfilaria will be missing from about 30% of infected dogs and most of the infected cats. Therefore serological techniques are usually used to make a diagnosis. In dogs and cats we can look for Antigen produced by mature female worms (over 6 months of age). In cats we can look for Antibody produced against heartworm larvae and adults which have been in the cat for more than 60 days (thus the antibody test tells us the cat was exposed, but not if there are adult worms present). In cats ultrasound of the heart and the base of the pulmonary arteries can show the presence of heartworm adults.
Common Diagnostic Tests
Pharmacueticals or surgery to remove worms.
For recommended treatments for dogs and cats go to the American Heartworm Society's Web site:
Thiacetarsamide sodium - Trade name: Carparsolate (no longer sold in the US)
Melarsomine dihydrochloride - Tradename: Immiticide
Ivermectin - Trade names: Heartgard Plus, Heartgard 30, Iverhart Plus,
Advantage® Duo, Tri-Heart Plus Chewable Tablets, Heartgard for Cats
Moxidectin - Trade names: ProHeart, ProHeart 6
Milbemycin oxime - Trade names: Interceptor, Sentinel
Selamectin - Trade name: Revolution
Diethylcarbamizine - Trade name: Filaribits
© University of Pennsylvania 2004
Comments or Questions please contact: Dr. Nolan at: