Heartworm disease is a dangerous, potentially fatal condition caused by parasitic worms that live in a dog’s heart, lungs, and arteries. While it is a serious threat, the good news is that heartworm disease is preventable with proper care and consistent use of medication.
How Do Dogs Get Heartworm Disease?
Heartworm disease is transmitted by mosquitoes carrying infective heartworm larvae. Not all mosquitoes are carriers—only those that have previously fed on an infected animal.
- When a mosquito bites a dog, it injects larvae into the skin.
- These larvae enter the bloodstream and migrate to the heart, lungs, and arteries.
- Within about five months, they grow into spaghetti-like worms that can reach up to 12 inches long and live for up to seven years inside a dog’s body.
Dogs, coyotes, foxes, and wolves are considered natural hosts and are highly susceptible to infection if not protected with preventive medication.
The Life Cycle of Heartworm Disease
Mosquitoes play two major roles in spreading heartworm disease:
- Infecting dogs – By biting and injecting larvae into a dog’s bloodstream.
- Spreading the disease further – By ingesting microscopic baby worms (microfilariae) from an infected dog, which then develop inside the mosquito and can be transmitted to other animals after 10–14 days.
This cycle makes mosquitoes the essential link in the spread of heartworms.
Is Heartworm Disease Contagious Between Dogs?
No. Heartworm disease cannot spread directly from one infected dog to another. Only mosquitoes can transmit the larvae. However, any time there are mosquitoes and infected animals in your area, unprotected pets are at risk.
How Are Heartworms Treated in Dogs?
If a dog becomes infected, veterinary treatment is required immediately.
- Treatment involves multiple medications, strict rest, and several months of careful monitoring.
- Even with treatment, heart and lung damage may be permanent, as worms cause inflammation, arterial thickening, and heart enlargement.
- If left untreated, heartworm disease can lead to heart failure and death.
Because treatment is costly and the damage irreversible, prevention is always the better choice.
Preventing Heartworms in Dogs
Prevention is simple, safe, and effective.
- Start early: Dogs can begin heartworm prevention at 6–8 weeks of age. Older dogs should be tested before starting prevention.
- Highly effective medications: When given correctly, heartworm preventives are nearly 100% effective.
- Formulations: Options include monthly chewables, topical solutions, and long-lasting injectables. Some products also protect against fleas, ticks, and intestinal parasites.
- Consistency matters: Preventives must be given on time, year-round. Missing doses puts dogs at risk, even in colder climates, since mosquitoes can survive indoors and in protected areas.
The American Heartworm Society recommends year-round prevention for all pets—including dogs, cats, and ferrets.
Heartworm disease is serious but entirely preventable. Keeping your dog on consistent preventive medication is one of the simplest, most cost-effective, and lifesaving steps you can take as a pet parent.
Prevention not only protects your dog’s heart and lungs but also ensures a healthier, happier life free from this devastating parasite.
