Should Dogs and Cats Take Heartworm Preventatives

Written by Small Door's medical experts

Heartworm disease is a serious, progressive and potentially fatal infection in pets, with few early signs of infection. For dogs, prevention is far superior to heartworm treatment – and for cats, there is no treatment for heartworm. Preventing your pet from becoming infected is better for their health, less expensive, and much less time-consuming than treating heartworm itself.

What is Heartworm Disease?

Heartworm disease is transmitted by baby worms carried by mosquitoes. When the mosquito bites a pet, the worm enters the bloodstream of the pet and can grow up to a foot long as it matures, taking up residence in the heart and lung blood vessels, damaging the internal organs.

Once inside a host, the larvae develop into mature adult heartworms in about 6 to 7 months. Heartworms can live for 5 to 7 years in dogs and 2 to 3 years in cats.

Heartworm infection has the potential to occur wherever there are mosquitoes. It has been found in all 50 states and even in climates that people assume are safe. (Even desert areas may have irrigation drainage and other opportunities for mosquitoes to propagate.) Some pet owners think that they can stop giving their dogs and cats heartworm preventatives in the winter, but because of the parasite’s long maturation process, this puts pets’ health at risk.

Dogs are more likely to contract heartworm disease than cats, and they are known as a ‘natural host species’, which means that heartworms living inside a dog are able to mature into adults, mate, and produce offspring. Left untreated, heartworm numbers can increase, and infected dogs can potentially harbor hundreds of worms.

While heartworm disease is more common in dogs than cats, cats can also contract heartworms. Unfortunately, even a small number of heartworms in cats can result in a medical condition called heartworm-associated respiratory disease, a lung disease that can cause severe breathing difficulties.

What Should I Know About Heartworm Preventatives?

Preventatives are regular (usually monthly) medications that you should give your pet to protect them from heartworm. There are a number of different brands and types of preventatives, including pills/chewables, topical medications and injections. Whichever type you choose, they need to be applied year-round in order to keep your pet safe.

Heartworm preventatives work by eliminating the early (larval) stages of the heartworm parasite, before they can mature into worms.

As heartworms can mature from larvae to worms quickly (sometimes in as few as 50 days), and then can no longer be eliminated by preventatives, it’s extremely important to administer preventatives on a strict schedule.

Can Pets Still Get Heartworms While on a Preventative?

While heartworm preventatives are highly effective, they are not 100% foolproof. Not following a strict schedule of administering preventatives raises your pet’s risk of infection. Sometimes pills are not swallowed, or they may be thrown up. Topical creams can be washed or licked off if not applied correctly.

It’s therefore important to test your pet for heartworm every 12 months, as well administering a monthly preventative.

There is also a possibility that administering heartworm preventatives to a heartworm-positive pet may cause a severe, life-threatening reaction, depending on the extent of the infestation. This is another key reason heartworm testing is so important.

Heartworm testing requires a small blood sample, which is tested for proteins that indicate the presence of heartworms.

Preventing your pet from becoming infected is better for their health, less expensive, and less time-consuming than treating heartworm itself.

What Happens if My Pet Tests Positive for Heartworm?

If your pet tests positive for heartworm antibodies, additional tests may be required to determine the extent of the infection. An antigen test can provide a definitive diagnosis of mature worms living inside the pet, and a chest x-ray can evaluate if there has been any damage to the lungs or heart.

Is There a Cure for Heartworm?

There is no treatment for heartworm disease in cats, only supportive care, which makes heartworm prevention even more important. Treatment manages any clinical signs that develop, such as breathing difficulties or a cough. This treatment may include steroids to decrease inflammation in the lungs. Occasionally, cats may be able to clear the infection themselves; further testing can determine if this is the case. Unfortunately, some cats can pass away suddenly from heartworm disease, although this is not that common.

There is a treatment for dogs, which takes an average of about 6 months to complete, during which time your dog must stay on bed rest. The treatment itself is also not without risk, because the process of killing heartworms can cause a severe, life-threatening anaphylactic (allergic) reaction. Heartworm treatment is also expensive and the injections can be painful for the dog. For these reasons, heartworm prevention for dogs is by far the best option, and treatment – if needed – should be administered as early as possible.

What Heartworm Preventative is Best for My Pet?

There are a number of different heartworm preventatives available. One that we often recommend is a chewable tablet flavored to taste appealing to pets, known as Heartgard.

Certain preventatives may suit your pet best, depending on their breed, health conditions and lifestyle. It’s also extremely important to administer the correct dosage for your pet’s weight, to ensure your pet receives a strong enough dose to kill all heartworm larvae, or conversely that your pet receives too strong a dose.

You should talk to your vet about which preventative is best for you. They can also answer any other questions or concerns you may have about heartworm preventatives.

It’s best to avoid herbal and homeopathic heartworm preventatives and treatments, because there are no scientific studies to prove their effectiveness. Some, including wormwood and black walnut, may even be toxic in large doses.

Heartworm Prevention Is Worth It.

Spending a minute or two, once every month, to administer preventatives can save you a lot of time, hassle, pain, and money down the road. Speak to your vet for further advice on how you can begin a heartworm preventative schedule as soon as possible for your pet.