Heartworm in Cats: What You Need to Know

15 May 2019

Heartworm in Cats: What You Need to Know

Heartworm is a horrible disease that affects millions of cats. So what is it, where does it come from and how does it affect our feline friends? We’ll answer these questions for you and what to do if your cat contracts Heartworm. It can be potentially fatal if not treated and can be found in many parts of the world. It’s important to know about these sort of diseases and what to look out for, as well as where it comes from. This article will tell you how to protect your kitty from this horrible illness.

What is Heartworm?

Heartworm is caused by worms (roundworms), that can often grow to around a foot in some animals, that live in main organs, like the heart and lungs. This causes lung disease and heart failure. It can also cause damage to other organs, which of course just shows how dangerous and fatal it can be. Heartworm in cats isn’t as serious as in dogs, and fewer worms are usually found in cats. Although, it is still very important to treat this and the severity depends on how many worms are present in the body. Generally, Heartworms found in cats have a shorter lifespan to dogs and outdoor cats are more likely to contract the disease.

Heartworm can also be found in dogs and ferrets, and many wild animals like wolves and foxes. It can spread very easily and can go undetected for months, which is why it is so important to understand how to catch and treat this disease. The medical term for Heartworm is 'Dirofilaria Immitis, which is quite a mouthful, so it is usually just referred to as Heartworm disease!

Where Does Heartworm Come From?

So now we know what Heartworm is, where does it come from and how is it spread? The main way it is spread is through mosquitoes (like many diseases). If the mosquito takes blood from an animal infected with Heartworm, they can pick up baby worms or ‘microfilaria’ from the blood and carry it to the next animal they bite, which may be a healthy cat. If the baby worms have reached the infective stage, this larvae can then be transported into the next animal the mosquito bites. Once the worms are inside the cat, it takes around 6 months for the larvae to develop into adult Heartworms, however, it is rare for Heartworms to reach this stage in cats. Fur babies can be infected many times during mosquito season, so be aware of this increased risk. In dogs, when the Heartworms reach the heart and lungs, they release microfilaria into the blood. The presence of microfilaria in cats blood is actually uncommon and cats are more likely to have a spontaneous recovery. This is because the lifespan of Heartworms in cats is much shorter than in dogs.

When is Mosquito Season and How Does it Correlate with Heartworm Disease?

You are probably well aware of mosquito season, but for clarity, these little pests usually thrive when the temperature rises above 50 degrees Fahrenheit, so this can be from the start of Summer all the way to the colder months. In the Southern states, you are probably used to seeing mosquitoes for many months of the year due to the warmer climate. The more mosquitoes around, the more at risk your fur baby may be of Heartworm disease. Mosquitoes can travel long distances in the wind, so the disease can spread over quite some distance. As we know, mosquitoes can get inside the house with ease, meaning your feline friend may even be at risk in the comfort of their own home. Veterinarians will usually test for Heartworm in the Spring, to test for the disease that could have been contracted from the previous mosquito season. Mosquitoes usually live for a few weeks, and in that time, the females can lay up to 100 eggs, so you can see how much of a problem Heartworm can be. Heartworm cannot infect humans, and even if the mosquito spreads the larvae to you, it will never develop into adult worms which cause the disease. It is more serious in dogs but it still important to get treatment for your cat. Treatment to prevent Heartworm is relatively inexpensive and is well worth the protection against this disease, which if left to develop, can be fatal. Cats cannot spread the disease to any other cats and the disease can only be spread through mosquitoes – they are the sole culprit.

What are the Signs of Heartworm Disease in Cats?

So, how do you know if your cat has Heartworm disease? It’s a horrible thought and many pet parents dread this sort of illness from happening. During the early stages, there aren’t many symptoms, unfortunately, so it is hard to detect if your cat has Heartworm. You may not know until your cat is heavily infected. The Heartworms spread the disease when they mature into adults and this is when you will start seeing the symptoms. You may see some of these changes on symptoms in your feline friend.

The signs you should look out for are:

  • Coughing
  • Fatigue
  • Vomiting
  • Weight loss

Heartworm disease in cats is very different from Heartworm disease in dogs. Most cats who have the disease have no adult worms, however, the immature worms can cause real issues and damage to your cat, and can go undetected, making it much more of a risk. Cats who do have adult worms only have a few and they do not grow as large as they can in some other animals. According to the American Heartworm Society, these baby worms can cause ‘Heartworm Associated Respiratory Disease’. Medication to treat cats who have Heartworm is not available, so preventative medication is the only way to protect your cat from Heartworm disease.


How is Heartworm Disease in Cats Diagnosed?

So, if Heartworm is difficult to detect in cats, how is it diagnosed? If you are noticing breathing problems, coughing or any other symptoms in your cat, book an appointment with your vet. If your cat is displaying these symptoms, your vet may do a few things to see if it is Heartworm, even though there are no specific tests to diagnose Heartworm in cats. This is because of the fact that it is unlikely that your cat will have adult worms in them. Tests may include urine analysis, x-rays, an electrocardiograph or antigen tests. So even though there aren’t specific tests, these checks are a great way to understand your cat's health, especially if they unwell with the symptoms. These tests will also determine other heart diseases.

What if My Cat Tests Positive for Heartworm?

There are differences in the disease between cats and dogs. Dogs will require a course of treatment to break down and kill the worms, which can take months. It is better to treat your cat before they get Heartworm, as there isn’t a treatment for them if they are diagnosed. The infection usually leaves your feline friend on its own as cats aren’t an ideal host for Heartworms, which is a good thing. However, the disease can cause respiratory problems and affect the immune system. In severe cases, it may spread to the brain, spinal cord and eyes and may cause blood clots and lung inflammation. When they are diagnosed, cats usually have only 6 worms or less. However, just having these worms can make your cat very poorly. Your vet will take blood tests and an x-ray to find and diagnose accordingly.

As there is no approved drug treatment for cats who have Heartworm disease, your vet may stabilize your cat and will create a long term care and management plan to help. This will depend on the severity of the disease. Your cat will then need to be monitored and checked every 6 or 12 months to see how the clearing of the disease is going. Anti-inflammatory medicines may be used to help. If the disease is particularly bad, your veterinarian may need to perform surgery or treat your feline friend for damage to their heart and lungs.


How Can You Treat or Prevent Heartworm Disease in Cats?

Preventative care is the best way to protect your four-legged friend from Heartworm disease. This can be through a pill, injections or spot on medication which work to kill the larvae if a mosquito carrying the disease were to transfer it into your cat. These should be strictly administered monthly, to ensure your fur baby is fully protected. In just 50 days, the larvae can grow into adults, which can’t be eliminated by the preventative medication. Your vet may perform annual checks on your cat, which will help to detect Heartworm. You can start your cat on preventative medication from 8 weeks old and the dosage will depend on body weight. Your vet will be able to advise you on this treatment if you have any questions


What Do I Do if I Think My Cat Has Heartworm Disease?

Contact your vet immediately and get an appointment. They will be able to test your cat and get the results very quickly, so a diagnosis won’t take long. Remember, if your cat has Heartworm, it is likely that they will be able to eliminate them naturally, but your vet will also create a care plan to help. Make sure your cat is placed on preventative medication to ensure they don’t get Heartworm again. Year-round Heartworm preventative medicines are heavily advised, even in the colder months when mosquitoes aren't all over the place. Sticking to a monthly course of preventative medicine will keep your cat safe, and if your kitty has had Heartworm disease before, they can get it again. Heartworm treatment can be expensive, especially if your cat requires surgery, which is another way the preventative medicine helps pet parents.  


How is Heartworm Associated Respiratory Disease Treated?

Heartworm Associated Respiratory Disease (HARD) is essentially the illness that cats contract from Heartworm. As we explained before, there is no significant treatment for cats with Heartworm, which is the same for HARD. Your vet will likely treat your feline friend with anti-inflammatory medicine and keep an eye on their recovery. They may use other treatments like fluid therapies or cardiovascular support. This disease is easily prevented through Heartworm preventative medicines, so make sure you keep up with this to avoid this illness from affecting your cat.



To conclude, Heartworm disease is one of those horrible diseases that you wish didn’t exist. Luckily it is not so serious in cats, but you should never take it lightly. The symptoms of Heartworm may not show for some time, so it’s important to get regular tests for your cat. These are usually done annually as part of your pet’s routine tests. If your pet does have Heartworm, symptoms that develop over time may be coughing, vomiting and weight loss. The disease will usually manifest itself as Heartworm Associated Respiratory Disease (HARD). In severe cases, your cat may contract this disease of the lung, which can cause permanent damage. There is no significant treatment for Heartworm in cats, as cats aren’t such a good host for them, but they can still be spread to them and cause problems. Remember, this can be spread by a single mosquito bite, and the disease has been found in all 50 states. Speak to our veterinarians at FetchMyVet.com if you are worried or have anymore questions about Heartworm, and make sure to treat your feline friend monthly with Heartworm preventative medicine.

Category: Preventive Care

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