Heartworm Disease
A serious, potentially fatal parasitic infection caused by foot-long worms residing in the pulmonary arteries and heart.
💬 In Plain English
Heartworm is transmitted exclusively through the bite of an infected mosquito. Mosquitoes inject microscopic heartworm larvae (Dirofilaria immitis) into the pet’s bloodstream. Over 6 to 7 months, these larvae mature into foot-long adult worms that live inside the pulmonary arteries leading from the heart to the lungs. The worms cause severe inflammation, blood clots, pulmonary hypertension, and heart failure. While dogs can harbor dozens of worms, cats are atypical hosts where even 1 to 2 worms can cause severe asthma-like lung inflammation (HARD) or sudden death.
🔬 Clinical & Technical Depth
For Vets & TechniciansFormal Clinical Definition
Infection by the nematode Dirofilaria immitis. Adult worms inhabit the pulmonary arterial tree, triggering endarteritis, pulmonary hypertension, cor pulmonale, and right-sided congestive heart failure. Caval syndrome occurs when large worm burdens retrograde into the right atrium and caudal vena cava.
Why Veterinarians Use It
Veterinarians run annual heartworm antigen tests to detect female adult worm proteins before irreversible vascular damage occurs.
Clinical Context Encountered
Prevalent in mosquito-dense climates across North America, diagnosed on routine annual screening or when dogs present with coughing and exercise fatigue.
Clinical Reference Guide (Medical Condition)
- •During heartworm adulticide treatment, dying worms fragment and lodge in the lungs. Failure to maintain strict crate rest can cause fatal pulmonary thromboembolism.
- •Caval syndrome (sudden collapse, pale gums, and red wine-colored urine) is an immediate surgical emergency requiring mechanical transvenous worm extraction.
❓ Questions to Ask Your Veterinarian
Take these actionable questions with you to your next clinic visit or appointment:
- 1Did the annual screening test detect heartworm antigen or microfilariae?
- 2Has the positive result been confirmed with a secondary verification test per American Heartworm Society guidelines?
- 3What American Heartworm Society adulticide protocol (doxycycline + 3-dose melarsomine) is recommended?
- 4Why is strict, absolute cage rest essential during melarsomine adulticide treatment?
Academic & Clinical References
- Current Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm InfectionOrganization: American Heartworm Society (AHS) • Published: 2024-01-01 • Accessed: 2026-01-10https://www.heartwormsociety.org/guidelines