How Do Dogs Get Heartworm?

Many dog owners are surprised to learn how heartworm is spread. If you're asking how do dogs get heartworms, the answer lies in one of nature's most common pests: the mosquito.

Understanding how heartworms are transmitted can help you take the right steps to protect your dog before it's too late.

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What is heartworm disease?

Heartworm disease is a serious and potentially fatal condition caused by a parasitic worm called Dirofilaria immitis. These worms live in infected dogs' hearts, lungs, and associated blood vessels. Adult heartworms can grow up to 30 cm long. Heartworm disease is most common in warmer regions, although cases have been reported all over mainland Australia.

What causes heartworms in dogs?

The heartworm life cycle involves several steps:

- Microfilariae

In an infected dog, adult female heartworms living in the heart and lungs release microscopic offspring called microfilariae into the bloodstream. These tiny larvae circulate in the infected dog’s blood.

- Mosquito transmission

When a mosquito bites an infected dog, it ingests blood containing microfilariae. The mosquito becomes a carrier, setting the stage for transmission to other dogs.

- Development in the mosquito

Inside the mosquito, the microfilariae develop into infective larvae over 10 to 14 days. These larvae migrate to the mosquito’s mouthparts, ready to be transferred to a new host.

- Infection in a new dog

When the infected mosquito bites another dog, it deposits the larvae onto the skin. The larvae enter the dog’s body through the mosquito bite wound.

- Larval maturation

Once inside the dog, the larvae migrate through the tissues, eventually reaching the heart and lungs. It takes around 6-7 months after infection for the worms to mature into adults and start reproducing, continuing the cycle.

Why are heartworms a problem?

Heartworms can live silently in a dog's body causing damage long before symptoms appear. Left untreated, heartworm disease can be life-threatening. Signs or symptoms of heartworm may include:

Coughing
Exercise intolerance
Weight loss
Breathing difficulty
Swollen abdomen
Collapse
Sudden death

Treating heartworm disease requires complex and potentially costly treatment by a veterinarian and comes with potential risks.

How to prevent heartworms in dogs?

As with most parasites, preventing heartworm is far safer, easier, and more affordable than treatment. Vet-recommended heartworm preventatives like NexGard SPECTRA^® are highly effective. It’s important to continue heartworm prevention all year round.

FAQs

Can mosquitoes cause heartworms in dogs?
Yes. Mosquitoes are the only way heartworms are transmitted from one dog to another. Without mosquitoes, the heartworm life cycle cannot continue.
Can dogs get heartworms from drinking water with mosquito larvae?
No. Mosquito larvae in water do not cause heartworm disease. Only adult mosquitoes transmit heartworm.

What puts a dog at risk for heartworm?
Any dog exposed to mosquitoes is at risk. This includes dogs living in warm, humid regions, dogs who spend time outdoors, or even indoor dogs in areas where mosquitoes are present.