Heartworm...it's serious

Heartworm is a potentially serious and deadly disease but fortunately is also a completely preventable disease.

 Keep your dog healthy and happy and free from worms: see your team @ The Pines Vet

Keep your dog healthy and happy and free from worms: see your team @ The Pines Vet

We show you what the signs to look out for if your pet has worms, and how they can be treated:

Heart worm disease is caused by parasitic worms that transmitted to primarily dogs, but also cats, by the bite of an infected mosquito. It takes these parasitic worms 6-7 months to mature and migrate to the major vessels of the heart and lungs. The adult worms then breed and produce their offspring, known as microfilaria, which can be found in the blood stream. A mosquito then bites the infected dog or cat and becomes infected with the microfilaria. The heart worm requires an incubation period in the mosquito before being able to infect other animals and thus continuing the cycle.

It only takes one bite from an infected mosquito to cause heartworm infection and there is no other way for dogs to contract the disease.  Unfortunately even completely indoor pets are at risk as there is no full proof way to keep these pesky critters out of ours houses and homes, even with fly screens.  Hence why prevention is so important. Heartworm is a specific parasite that affects dogs, less frequently cats and a few other small mammals. In very rare cases, it has been reported in people causing lesions in the lung but it can’t complete its life cycle and produce microfilaria. 

Initially, there are few signs of infection in dogs. However as the heartworm/s grow and mature they crowd the heart and lungs and disease results from predominately the obstruction of the flow of blood due to their presence.  Most dogs develop a persistent dry cough and typically this occurs when half the lung capacity is affected. Over time dogs become less tolerant to exercise, become listless and weak, can start to lose weight and there coat condition changes. Advanced cases often present in heart failure with difficulty breathing, distended abdomens, major organ destruction has occurred and when left untreated is almost always fatal. 

Cats are a little different in that they show very few signs of disease. This is because disease predominately arises due to an inflammatory reaction generated by the presence of the worms. On occasions they may be vaguely unwell or present in heart failure but typically the main sign is sudden death. This is because a very low burden of just 1 or 2 worms can be fatal.

Screening for heartworm disease in dogs is relatively easy but can be more challenging in cats. In dogs a very accurate blood test can be performed at the vet clinic with results available before the end of a visit. A second blood test however maybe required 6 months later to ensure that your pooch is heartworm negative (this is due to the long development period to an adult heartworm). In cats the blood test isn’t as accurate as often disease can be the result of just one worm. False negatives are common, so further imaging (radiographs and ultrasounds) maybe required when the disease is suspected.

There is certainly treatment for dogs with heartworm infection but it’s not without its risk and potential complications. It is often a lengthy process which requires regularly rechecks at the vets and can become quite expensive in comparison to prevention. Cats can be very difficult to manage as they can’t receive the same treatment as dogs as this can be fatal, in some cases very invasive risky lifesaving surgery is required.


Heartworm disease is completely preventable. Dogs, ranging from 5-50kg, can be protected against heartworm for 12 months with a once a year injection for a little less than the average weekly cup of coffee. There are also monthly tablets and spot on treatments available but your pets are at risk of infection if even just 1 month is missed. If you’re unsure on your pet’s heartworm prevention status come in and see us to discuss your pet’s options at The Pines Vet.