Heart Felt Concerns

The thought of a large worm-like alien wriggling around inside your heart, growing relentlessly inside your defenceless body by feeding on your own blood and slowly but surely sending you to your maker makes for the beginnings of an award-winning horror movie.

However, when heartworm disease infects our dogs and cats, this is a real-life horror.

It seems that heartworms have been killing pets for centuries. The first published records of the infection in dogs occurred in 1847 and in cats in the 1920's.

As well as dogs and cats, heartworms have also been found in wolves, foxes, coyotes, ferrets, in various big cats and even in bears, horses and in humans. In humans, the disease is mostly discovered when a radiograph has been taken. The difficulty is that the 'coin lesions' caused by the worms resemble lesions caused by lung cancer.

Is Your Pet Likely to have Heartworm Disease?

If your dog or cat is on a heartworm preventive that is being given regularly, then heartworm disease is unlikely.

If your pet is in a heartworm-infected area and if the preventive is not being given regularly then infection is more likely and it is very likely where dogs receive no preventive medication.

In cats, the disease is less common because cats show more resistance to infection. Experimentally, when cats and dogs are deliberately infected with heartworm larvae, the larvae will grow to adult size in up to 25% of cats but in dogs up to 90% are thus affected.

What effects does HWD have on a pet?

In a dog, the disease is usually progressive and infection can be present for months or years before a problem is noticed.

A worsening cough is usually one of the first signs. The dog then becomes inactive and lethargic due to the weakening of its heart. It will not be able to tolerate exercise without coughing.

In severe cases, fluid leaks out of the blood vessels and accumulates in the lungs and the lower part of the abdomen. This fluid gives the dog's abdomen a 'pear-shaped' appearance, resembling the shape of a balloon filled with water.

Sometimes, the animal will suddenly collapse. This is associated with deep, laboured breathing, extreme weakness, the development of a blue appearance to the tongue and paleness of the gums.

In cats, serious disease can be caused with just one worm, whereas in dogs, one or two worms are usually well tolerated. Tragically, the most common sign of the disease in cats is sudden death. Heartworm disease is very difficult to diagnose in cats because the signs seen are vague and can be mimicked by other diseases.

How is Heartworm Disease Diagnosed?

Your veterinarian may suspect heartworm disease if your pet is showing any of the signs mentioned above. He or she will do a cardio-vascular examination which will include listening to your pet s chest with a stethoscope, a process called auscultation.

The next step is usually a blood test but it is likely that X-rays and possibly angiography, (where a contrast dye is injected into your pet's blood stream) will be recommended. Ultrasound is also commonly used.

What treatments are available?

Unless your dog is seriously affected by the disease, treatment is usually successful.

With dogs, your veterinarian is likely to want to kill the adult worms and also the microscopically small young worms, called microfilaria, in your dog's blood stream.

There are various medications available to your veterinarian for this purpose.

With cats, treatment is difficult because the medications used in dogs may not be tolerated by cats. Compared with the infection in dogs, heartworms live for a shorter time in cats, therefore, some cats will recover without treatment. If significant signs of disease are present in a cat, a variety of supportive treatments are used to treat the condition.

How can the heartworm disease be prevented?

Thankfully, preventing heartworm disease is easy and all dogs and cats should be on some form of preventive medication.

There are several choices. A daily heartworm preventive has been available for dogs for many years but has been mostly superseded by modern preventive preparations.

Monthly heartworm medications are popular. Some are available as tablets, some as chews but the most popular monthly products are the 'spot on the back of the neck' preparations. Many of these also help to control intestinal worms.


 Heartgard Chewables  Cat Health Products  ProHeart    


A recent advance in heartworm prevention is the yearly Once-A-Year Heartworm Prevention injection.

The advantage of this injection is that you only have to remember your dog's heartworm preventive once a year rather than trying to remember it every day or each month. The injection can be given to your pup at three months of age along with its puppy vaccination and from then on it's an easy matter because your vet will usually have a reminder system in place to keep you up-to-date on your pup's future heartworm and vaccination needs. So if your have a better 'forgetory' than a memory your pet's health will not be at risk!

So, at last your heart-felt concerns are gone. The real life horror of heartworm disease and its lethal effects can now be a thing of the past.


For further advice on this topic, start by completing a Behaviour Assessment Form on Dr Cam's Pet Health site - www.pethealth.com.au