Does my cat need heartworm prevention?

Updated November 29, 2020

In the 1990’s something weird was happening to cats in Adelaide. It may have been happening sooner but it was certainly in full swing when I graduated in 1994. It was dramatic and awful, and we really couldn’t explain it at the time.

Each time it happened the scenario was remarkably similar: all of a sudden a cat would be rushed down to us in severe respiratory distress. It was horrible to watch these cats as they struggled for each breath and became more and more frantic. X-rays showed their lungs to be ‘whited out’ with pulmonary oedema, or fluid on the lungs. Almost always, nothing could save them. We would put them on 100% oxygen, administer diuretics, cortisone, bronchodilators, adrenalin but they usually died quickly.

This was all very strange but the strangest thing was that these cats had often seemed perfectly fine only minutes before this happened.

I still can’t say with certainty what was happening but here are three reasons I think it was feline heartworm disease:

• We were in the middle of the worst heartworm epidemic in dogs at the time
• These strange events stopped when we got the disease under control in dogs
• The symptoms of heartworm in cats were later found to be exactly the same (read about the symptoms of heartworm in dogs here).

At the time, the fact that cats got heartworm was well-known, but the symptoms were not well understood. We didn’t even think of heartworm at the time, but of course there was never going to be any way to save these cats even if we did.

What we know now is:

• Heartworm is a disease originating in dogs which can affect cats and ferrets.
• When it does, it is seen at roughly 10% of the rate at which the dogs get it.
• When it infects a non-typical host it causes severe and rapid disease (like Ebola does in humans).
• The symptoms are usually of anaphylaxis which is a severe immune reaction. In cats this usually causes fatal pulmonary oedema.

My personal opinion is that although many more dogs than cats got heartworm at the time (probably over 10%), more cats died than dogs. We’ll never know because they were not able to be tested at the time. Many dogs survived due to attentive owners, and we treated a lot successfully. Heartworm infection in cats may have been rarer, but the consequences were rapid and severe. And I dread that many more cats died when no one was watching.

So to the big question: should you use heartworm prevention for your cat? My answer is yes. Why?

• Two good flea controls include heartworm protection without having to spend a lot more.
• The disease may be uncommon in cats, but the consequences are terrible.
• Prevention is safe and easy to apply. Read more at Parasite control for cats
• The is no approved treatment once a cat acquires heartworm.

You will never hear me telling you it is necessary, or that you are neglectful for not using heartwormers in cats. The way most people decide what to do is quite lovely; they ask me what I use. I always told them my cat got a dose of Revolution every month.

One of the advantages of getting older (yes, there are good things!) is being able to look back to when things were different to today. We’ve come a long way as vets in pushing back the effects of distemper, nutritional disease, feline enteritis, parvovirus, mange, and most recently heartworm.

All of these diseases are not beaten, but with proper vigilance our pets should never experience them again. The danger is now in relaxing our guard or listening to cynics who say these protections are unnecessary.

To those who say vets’ advice is motivated by money, I would ask you to do one thing for me. The next time the AVA Annual Conference is in your town, go down to watch the delegates milling around between lectures. You’ll see young and old faces, mostly female these days, all carrying the same expression of earnest thirst for knowledge. If you eavesdrop a conversation, it will almost always be about a patient they are struggling to treat, of something they have just learnt. A few will be bragging about some rare disease they diagnosed or new technique they’ve mastered. No one is talking money and they’ve all spent a lot of it just to be there.

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By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here.