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Dirofilaria immitis Homepage

          Common name: Canine heartworm

            Kingdom: Animalia

              Phylum: Nemathelminthes

                Class: Nematoda

                  Order: Spirurida

                    Family: Filariidae

                      Genus : Dirofilaria

                        Species: immitis

Visit the CAL 97 project on Canine Heartworm

Visit the  Dirofilaria immitis CAL life cycle page

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Adult Parasite:

The adult worms measure 15 cm (male) to 30 cm (female).

Adult worms: male and female (left), worms in situ (right)

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Hosts:

  • Dogs, cats, ferrets, seals (definitive).
  • Mosquitoes (intermediate) .

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Life Cycle:

    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.

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Site in host where adult parasite is found :

  • The pulmonary arteries and sometimes the right atrium.

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Diagnostic Stage:

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.

  • Microfilariae are found in blood smear using acid phosphatase stain:

Common Diagnostic Tests
  • Antigen Tests
  • Antibody Test (cats)
  • Blood smear
  • Modified Knott Method .
  • Filter test
  • Ultrasound (cats)  This is a real time movie of an ultrasound of an infected cat.  It is a very large file and it is recommended that you do not download this if you are using a modem connection.
  • Ultrasound (ferrets)  This is a real time movie of an ultrasound of an infected ferret.  It is a very, very large file and it is recommended that you do not download this if you are using a modem connection.

 

Clinical Signs:
  • Asymptomatic in dogs with low worm burdens.
  • With greater worm burdens exercise intolerance, hypertension, right heart failure may be seen.
  • Sudden death may be the only clinical feature seen in some cases of feline heartworm.

Treatment:

Pharmacueticals or surgery to remove worms.

For recommended treatments for dogs and cats go to the American Heartworm Society's Web site:

http://www.heartwormsociety.org/AHS%20Guidelines-Canine.htm

Adulticides

Thiacetarsamide sodium -  Trade name: Carparsolate (no longer sold in the US)

Melarsomine dihydrochloride - Tradename: Immiticide

 

Prophylactics

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

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© University of Pennsylvania  2004

Comments or Questions please contact:  Dr. Nolan at: