Heartworm Disease

mosquitoHeartworm disease (HWD) is a debilitating and life-threatening condition that is challenging to treat. Prevention is the best approach for the well being of your dog or cat.

How is HWD spread?

Heartworm is spread by mosquitoes, so our sub-tropical Brisbane climate means the potential for infection is always present. When a mosquito bites an infected animal it feeds on blood that contains tiny heartworms or microfilaria. Once inside the mosquito, the microfilaria develop into the infective stage larvae. This stage takes around 10-14 days. When an infected mosquito then bites a dog or cat, the infective larvae enter the animal’s body through the bite wound. Once inside your pet, the worm larvae mature to adulthood over the next 6 months. Adult worms can live inside dogs for up to 7 years and up to 3 years in cats.


Dogs are the natural host for heartworms so this means worms mature, mate and reproduce inside the dog’s body. The result can be large numbers of worms that cause damage to your dogs heart, lungs and arteries.

Signs of HWD in Dogs

Early signs of HWD can include a mild persistent cough, reduced energy levels and decreased appetite. In advanced stages of the disease, worms can cause major blockages in blood vessels within the heart (Caval Syndrome) resulting in life threatening cardiovascular collapse. Emergency surgery is needed to remove the worms from blocked blood vessels.


HWD in cats is very different when compared to dogs. Typically cats have far fewer worms and often no adult worms. This can make diagnosing HWD in cats more difficult. Immature worms cause damage that can result in heartworm associated respiratory disease (HARD). It is important to note that there is NO DRUG APPROVED FOR THE TREATMENT OF HEARTWORM IN CATS.

Signs of HWD in Cats

Unfortunately the first sign of HWD in cats can be sudden collapse or death. Other cats may show asthma like symptoms, coughing, vomiting and weight loss.

When should my pet start Heartworm prevention?

There is no maternal protection against heartworm, therefore prevention should start at 2-3 months of age.

Puppies can start on monthly oral or topical medication from as young as 6-7 weeks of age. Injections are also available. ProHeart SR-12 injection is a once a year prevention for HWD in dogs. The first SR-12 injection can be given to puppies at around 12 weeks of age then again 6 months later. Yearly boosters are needed to maintain full protection.

Kittens can be protected from HWD from 6 weeks of age with either monthly topical preparations or chewables. Currently monthly medication is the only prevention for HWD available for cats.

Testing for the presence of heartworm is an important part of a Heartworm Prevention Program. If you think your pet may have been infected with heartworm a simple blood test will be recommended. If you are unsure about your pet’s heartworm prevention treatment, a blood test is advised prior to commencing a prevention program.


site design achilles creative