Heartworm Signs, Treatment and Prevention

What is heartworm?

Heartworm is a parasitic worm that can infect your pet through a mosquito bite. An infected mosquito injects a larval stage of the worm under your pet’s skin. These larvae mature in the pet’s organs for approximately six months, traveling through the body to the heart and blood vessels of the lungs. These adult worms  breed to produce microfilaria (baby heartworm) in the bloodstream which are then drawn up by a mosquito when it feeds on the pet, continuing the cycle once again.

Mosquitoes are hard to keep out of both the yard and house, so even your indoor-only pets are at risk.

How common is heartworm?

The prevalence of heartworm in Australia remains poorly understood. What we know is wherever there are mosquitoes, there is potential for heartworm. There are ongoing studies to help experts find out more about heartworm infection in pets, which will assist in the treatment and prevention of the disease. With the information currently available, it has been concluded that prevention is the best form of heartworm control.

What are the signs of heartworm?


Initially, it’s tough to tell that anything is wrong with your pet at all. Heartworm is a slow onset disease, so months or even years may pass before the signs become obvious. When symptoms do appear, your canine companion could have a large heartworm burden. Worms interfere with the movement of the heart valves, creating turbulence in the blood flow, and causing the blood vessels that lead to the lungs to become “blocked” with worms. This puts the heart under immense strain, where it can become enlarged and exhausted.

Early signs could be shortness of breath, loss of stamina, or a nagging, dry cough. As the disease progresses, breathing becomes more difficult, and in severe cases the abdomen may swell with fluid. Your dog could become lethargic and lose weight and their appetite. These symptoms are often subtle and hard to detect, so prevention is the best option. Treatment for heartworm disease is not without potential risk, may be  difficult, and if left untreated,  it is nearly always fatal.


Usually, there are few clinical signs of heartworm in cats. Your cat could develop slight lethargy or a cough, but sudden death is more common if your cat’s heartworm has gone undetected and untreated. It only takes one to two adult heartworms infecting your furry feline for the disease to potentially become fatal.

CT scanner

How do I diagnose heartworm in my pet?

Have your pet tested at the vet. A simple blood test can reveal whether your pet is infected. Unfortunately, diagnosis is more difficult in cats, so prevention in all cases is always the best option. Keeping your pet up to date with regular heartworm medication, paired with regular vet check-ups is the best way to ensure their health is optimised.

Can heartworm be treated?

Yes. However, prevention is far better than treatment. Since diagnosing heartworm can be challenging, especially in cats, your pet’s illness may be quite advanced and challenging to treat. Allergic reactions to heartworm treatments have been identified, and some of the treatments can have serious side-effects, so staying on the safe side and keeping your pet up to date with their heartworm prevention is strongly recommended.

Learn more about heartworm treatment here.

How do I prevent my pet from getting heartworm?


There are many heartworm preventatives available. If your dog has not had heartworm medication for more than six months, a blood test is necessary before you can commence preventative treatment, just to make sure they don’t already have heartworm. Prevention should begin at six to eight weeks of age. Medications come in either tablet form or as top-spot application, and many brands help protect your pet against intestinal worms and other parasites like fleas as well.  The most convenient and effective heartworm prevention is a yearly injection administered by your veterinarian. This can be given from 12 weeks of age, then boosted at 6 months.


Tablets or top-spot applications are the best products available to prevent heartworm infection in cats. You can purchase high-quality heartworm products that also cover intestinal worms, with some also controlling fleas. We know your cat can be difficult to medicate, so regular visits to the vet where a professional can administer them for you is a good idea.

Remember that prevention is always the best medicine. Keep your pet happy and healthy all year round by sticking to a good preventative treatment plan. They’ll thank you for it.

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