Dog Heartworm

The dog heartworm (Dirofilaria immitis) is a mosquito-borne roundworm whose adults live in the pulmonary arteries and heart of dogs, cats and other mammals. Heavy infections cause serious, sometimes fatal, heart and lung disease.

🧬 Field Guide Specimen: Open Dog Heartworm in the CRV Science Field Guide to log the specimen, see its place among the Ecdysozoa lineages in the Cladogram Explorer, and test your recall in the Red List conservation game.

Female worms release microscopic larvae (microfilariae) into the blood. A mosquito picks them up while feeding, they develop into infective larvae over about two weeks, and are passed to the next animal when the mosquito bites. It takes months before the larvae mature into adults. See Mosquito-borne disease.

Heartworms depend on an endosymbiotic bacterium, Wolbachia, for development and reproduction. Treatments therefore often include the antibiotic doxycycline along with drugs that kill adult worms. See Wolbachia.

Monthly macrocyclic lactone preventives such as ivermectin kill larvae before they mature. Heartworm is found throughout the United States and in warm regions worldwide, and climate warming extends the season for transmission.

• Wolbachia — the worm's bacterial symbiont
• Mosquito-borne disease — vector transmission
• Extrinsic incubation period — development inside the mosquito