Heartworm Disease

Also called: Dirofilaria immitis, dirofilariasis, heartworm

• Dogs
• Infectious (viral)
• Any

A parasitic worm transmitted by mosquitoes. Larvae migrate through the body to the arteries of the lungs and the heart, where they grow into large adult worms that cause progressive heart and lung disease. Adult worms live for years. Prevention is far easier than treatment.

Signs to look for

• Often none early on
• Later: cough, exercise intolerance, and lethargy
• Weight loss
• Signs of heart failure in advanced disease

How a vet diagnoses it

A blood antigen test plus detection of the worm's microfilariae, with imaging in advanced disease. Annual testing is recommended.

Treatment

Treating an established infection is complex — a specific drug (melarsomine) with strict exercise restriction — which is why prevention is strongly preferred. Prevention uses monthly oral or topical products, or a yearly injection.

Monitoring at home

Annual testing and year-round prevention as advised by your vet.

Who tends to get it

Dogs of any breed; risk relates to mosquito exposure. Australian note: heartworm is considered endemic but clinical disease is now rare and prevalence low, largely because preventives were introduced in the early 1990s. Higher-risk pockets persist (e.g. some Queensland populations, pig-hunting and wild dogs). Australian advice still favours ongoing prevention and annual testing.

Sources

• Merck Veterinary Manual — Heartworm Disease in Dogs, Cats, and Ferrets
• Australian Veterinary Association