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"Caring for cats isn’t what we do, it’s who we are!"

"Caring for cats isn’t what we do, it’s who we are!"


What Is Heartworm?

What Is Heartworm?

By: Faith P.

What is Heartworm? Heartworm is a disease that occurs most commonly in dogs, but it can also affect cats and ferrets. This disease could cause your pet to have severe lung disease, heart failure, other organ damage, and death when contracted. The parasite that causes heartworm is named Dirofilaria immitis. They are called heartworm because they reside in the heart, lungs, and associated blood vessels of the animal they infected when they are adults. 

Heartworm is transmitted mainly through mosquito bites. Your pet is the definitive host, which means that the worms mature into adults, mate, and produce offspring while living inside your pet. 

Heartworm in Dogs

Dogs are the natural hosts for heartworm. If untreated, the number of heartworms can increase, and dogs can harbour several hundred worms in their bodies. This disease causes lasting damage to the heart, lungs and arteries. It can affect the dog’s health and quality even after the parasites are gone. This is why heartworm prevention for dogs is by far the best option. If your dog has contracted heartworms, treatment should be administered as early as possible in the course of the disease. 

The longer the infection is there, the more likely symptoms will pop up. Active dogs, dogs heavily infected with heartworms, or other health problems often show signs. Symptoms of heartworm disease include mild but persistent coughs, less exercise, weariness after short activities, decreased appetite, and weight loss. As the infection continues, pets may develop heart failure and appear to have a swollen belly due to excess fluid in their abdomen. Dogs with large numbers of heartworms can develop sudden blockages of blood flow in the heart. This leads to a life-threatening form of cardiovascular collapse.

Dogs should get tested for heartworm annually; this can be done at annual vet check-ups without scheduling another appointment. Talk with your vet about preventative treatments available. Often it is a medicine chew that is easily administered to your dog.

Heartworm in Cats

Heartworms in cats are very different from the disease in dogs. The cat is not a typical host for heartworms, and most worms do not develop into the adult stage. Cats with adult heartworms would most likely have only one to three, and most cats affected by heartworms have none. Since adult worms are less likely to develop, the disease is often undiagnosed in cats. It’s important to know that immature worms can cause damage through a condition known as heartworm-associated respiratory disease. Furthermore, you cannot use the medication used for dog heartworm infections in cats, so prevention is the only way of protecting cats from heartworm disease.

Symptoms could include coughing, asthma-like attacks, vomiting, lack of appetite, or weight loss. A cat that has been affected may have difficulty walking, have fainting or seizures, or suffer from excess fluid in the abdomen. Sadly, the first sign can sometimes be the sudden collapse of the cat or sudden death.

Since it is more difficult to see the disease in cats, it is better to use both an antigen and an antibody test. Your vet may also use x-rays or ultrasound to find larvae. You should get them tested before treatment.

Heartworm in Ferrets

The disease in ferrets is a mix of the illness that we see in dogs and cats. Like dogs, ferrets are highly susceptible to infection. They can have more significant numbers of worms than cats, but like cats, a low number of worms can cause devastating diseases due to the small size of their heart. Heartworm disease is often more challenging to diagnose in ferrets. There is also no approved treatment, so prevention is crucial for both indoor and outdoor ferrets.

Symptoms of heartworm disease in ferrets are similar to those in dogs; however, they develop faster because the ferrets have smaller hearts. Having just one worm can cause severe respiratory distress in a ferret.

Diagnosing heartworm disease in ferrets can be more problematic. Your vet may recommend using both antigen testing and diagnostic imaging to detect the presence of a worm in the heart.


This disease is not contagious and is only transmitted by mosquito bites. This is important info to have if you have more than one pet at home. If one pet is showing signs, all pets in the home should still be tested. Heartworm can also very rarely be found in humans, but it is not likely to affect us and won’t survive to adulthood in our bodies. Heartworms can be very dangerous to your pet. It is in your best interest to take preventative measures and test your pet immediately if you think they may have heartworms.






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