Heartworm in Dogs: What Every Aussie Must Know

Heartworm disease is one of those conditions that sounds alarming — and for good reason. Left untreated, it can be fatal. But here is the reassuring part: heartworm is almost entirely preventable. If you are a dog owner in Australia, understanding how heartworm works, where the risk is highest, and what you can do to protect your mate is one of the most important steps you can take for their long-term health.

What Is Heartworm Disease?

Heartworm disease is caused by a parasitic worm called Dirofilaria immitis. These worms live in the heart, lungs, and associated blood vessels of infected dogs. Over time, adult heartworms — which can grow up to 30 centimetres long — cause serious damage to the heart, lungs, and other organs. A single dog can harbour dozens of adult worms, and the damage they cause can be permanent even after treatment.

It is not a condition that develops overnight. The lifecycle from initial infection to adult worms takes around six to seven months, which means your dog could be infected for quite a while before any symptoms appear.

How Do Dogs Get Heartworm?

Dogs cannot catch heartworm directly from another dog. The disease is transmitted exclusively through mosquito bites. Here is how the cycle works:

1. A mosquito bites an infected animal (dog, fox, or other host) and picks up microscopic heartworm larvae called microfilariae.
2. Inside the mosquito, these larvae develop over about two weeks into an infective stage.
3. When the mosquito bites your dog, the larvae enter through the bite wound.
4. The larvae migrate through your dog’s body over several months, eventually reaching the heart and pulmonary arteries where they mature into adult worms.
5. Adult worms reproduce, releasing new microfilariae into the bloodstream, and the cycle continues.

Because mosquitoes are the sole transmitter, any area with mosquitoes poses a risk — and in Australia, that covers a lot of ground.

Heartworm Risk in Australia: Where Is It Worst?

Heartworm occurs throughout Australia, but the risk is not evenly distributed. Northern and tropical regions — including Queensland, the Northern Territory, and northern Western Australia — have the highest prevalence. The warm, humid climate in these areas means mosquitoes are active year-round, giving the parasite more opportunities to spread.

Southern states like Victoria and Tasmania have lower rates, but the risk is not zero. Warmer months bring mosquitoes to every part of the country, and dogs that travel between regions can carry the infection with them. Vets across Australia recommend year-round prevention regardless of where you live, because even a brief lapse can leave your dog vulnerable.

Symptoms of Heartworm in Dogs

One of the tricky things about heartworm is that early-stage infections often show no symptoms at all. By the time signs appear, the disease may already be well established. Here is what to watch for:

Early Signs

• A mild, persistent cough
• Reluctance to exercise or tiring more quickly than usual
• Slight decrease in appetite

Moderate to Advanced Signs

• Difficulty breathing or rapid breathing
• A swollen belly (caused by fluid accumulation)
• Weight loss
• Lethargy and general weakness

Severe Cases

In heavy infections, dogs can develop a condition called caval syndrome, where the worm burden is so large it physically blocks blood flow through the heart. This is a life-threatening emergency requiring immediate surgical intervention.

If your dog shows any of these symptoms — particularly if they have missed prevention doses — see your vet promptly. A simple blood test can confirm whether heartworm is present. For more on recognising when something is off with your pet, have a read of our guide on signs your pet is in pain.

Heartworm Prevention Options in Australia

Prevention is straightforward, affordable, and far less stressful than treatment. Australian dog owners have several options:

Monthly Chewable Tablets

These are flavoured tablets your dog takes once a month. Most dogs happily eat them as treats. They work by killing any heartworm larvae that have entered the body since the last dose. Popular brands are widely available from vets and pet pharmacies across Australia.

Monthly Spot-On Treatments

Applied to the skin between the shoulder blades, spot-on treatments offer monthly protection against heartworm along with other parasites like fleas and intestinal worms. They are a good option if your dog is fussy about tablets.

Annual Heartworm Injection

Administered by your vet, this injection provides 12 months of heartworm protection in a single dose. It is an excellent choice if you worry about remembering monthly treatments. Many owners opt to schedule it alongside their dog’s annual health check.

Whichever method you choose, consistency is everything. A missed dose — even just one — can leave a window for infection. If you are ever unsure whether your dog’s prevention is up to date, your vet can run a quick test and get you back on track.

What Happens If Your Dog Gets Heartworm?

Treatment for heartworm disease is possible, but it is a serious and involved process. Here is what it typically looks like:

• Diagnosis and staging: Your vet will run blood tests and may use X-rays or ultrasound to assess the severity of the infection.
• Stabilisation: If your dog has significant symptoms, they may need initial treatment to stabilise their condition before addressing the worms themselves.
• Adulticide therapy: A series of deep muscle injections over several months kills the adult worms. This is the core of treatment.
• Strict rest: This part is critical. As the worms die, they break apart and are carried to the lungs where the body absorbs them. Too much activity during this period can cause dangerous blockages. Your dog will need to be confined and kept calm for weeks.
• Follow-up testing: Several months after treatment, your vet will test again to confirm the infection has cleared.

How Much Does Heartworm Treatment Cost in Australia?

The cost of treating heartworm in Australia can range from $1,500 to over $5,000, depending on the severity of the infection and any complications that arise. Severe cases requiring hospitalisation, surgery, or extended care can push costs even higher. Compare that with prevention, which typically costs between $100 and $300 per year depending on the method and your dog’s size.

This is where having a solid pet insurance policy can make a real difference. Many comprehensive pet insurance plans cover the cost of heartworm treatment, including diagnostic tests, injections, and follow-up care — provided it is not classified as a pre-existing condition. If your dog is young and healthy, getting them insured early means you are covered if the unexpected happens.

Keeping Your Dog Safe: A Quick Summary

Heartworm is a serious disease, but the good news is that protecting your dog is genuinely simple. Start prevention early — puppies can typically begin from around 12 weeks of age — and never let it lapse. If you live in or travel to northern Australia, be especially vigilant. And if you ever have doubts about your dog’s heartworm status, a quick vet visit can put your mind at ease.

Your dog relies on you for their health, and staying on top of heartworm prevention is one of the easiest and most impactful things you can do as a responsible pet parent.

Frequently Asked Questions

How do dogs get heartworm in Australia?

Dogs get heartworm through the bite of an infected mosquito. The mosquito picks up microscopic heartworm larvae when it feeds on an infected animal, then transmits them to another dog during its next bite. The larvae travel through the dog’s bloodstream and eventually mature into adult worms that live in the heart and pulmonary arteries.

Can heartworm in dogs be cured?

Yes, heartworm can be treated, but the process is lengthy, expensive, and carries risks. Treatment typically involves a series of injections to kill the adult worms, along with strict rest to prevent complications. Prevention is far safer, simpler, and more affordable than treatment.

What is the best heartworm prevention for dogs in Australia?

Australian dog owners can choose from monthly chewable tablets, monthly spot-on treatments, or an annual injection administered by a vet. The best option depends on your dog’s lifestyle and your preference. Talk to your vet about which suits your situation. The key is consistency — never miss a dose.

Does pet insurance cover heartworm treatment?

Many comprehensive pet insurance policies cover heartworm treatment as it is classified as an illness. However, cover depends on your specific policy, and pre-existing conditions are generally excluded. If your dog is diagnosed with heartworm before your policy starts or during a waiting period, it may not be covered. Always check your Product Disclosure Statement for details.