Dirofilaria immitis

Dog Heartworm; Heartworm


Phylum: Nematoda
Class: Chromadorea
Sub-class: Chromadoria
Order: Rhabditida
Dirofilaria immitis


Morphology and Anatomy:


Paleartic, Neartic, Oriental, Ethiopian, Neotropical, Australian, Oceanic Islands : Found on a world-wide basis, but very common in mild and warm climates

Economic Importance:

Veterinary fees, diagnostic tests, medicines for household pets.


Dogs, foxes, wolves, coyotes, and cats.


Dirofilaria immitis is a parasite which feeds exclusively on the blood of the host.

The nematode usually occupies the right chamber of the heart and the pulmonary arteries of dogs, foxes, wolves, coyotes, and cats.


Life Cycle:

(Lifecycle diagram from American Heartworm Society)

Dirofilaria immitis has an indirect life cycle. 

The adult parasite sexually reproduces in its vertebrate host, and the offspring are transferred to the intermediate host, which is usually a mosquito or a flea. 

The larva develops inside the intermediate host and molts twice.

When the intermediate host feeds, the larvae enter the new vertebrate host through the wound. 

The parasite remains dormant in the vertebrate hosts muscle tissue for 85 to 120 days. After this time period, the parasites enter the host's blood stream, where they are carried to the heart.

Completion of the life cycle in the heart requires 7 to 9 months.







American Heartworm Society

Olson, Wilford O. 1962. Animal Parasites-Their Biology and Life Cycles. Burgess Publishing Company, Minneapolis pp.315
Noble and Noble. 1964. Parasitology-The Biology of Animal Parasites. Lea and Febiger Co., Philadelphia pp.310

Material from Heather Hathaway, 1995.