Ginger fluffy cat is playful touching soft toy heart

If I had a dollar for every time… There are several questions that we as veterinarians hear over and over. Most of the time this means that it is a good question and there’s a lot of people that need to know the answer.  Previously, we discussed the answer to the common question “Does my dog need to be on heartworm prevention year round?”  Today, we are going to discuss another common question:

“Does my indoor cat really need to be on heartworm prevention all year?”

First let’s start with a review…courtesy of the American Heartworm Society

Heartworm is caused by a worm, Dirofilaria immitis.  Cats become infected with heartworms by a mosquito bite and then it takes 6-7 months for the heartworm to mature.  This worm lives in the heart, lungs, and blood vessels of the animal it has infected.  Adult heartworms live 2-3 years in the cat and can cause damage to the cat’s heart, lungs, and blood vessels, leading to heart failure, lung disease, and other organ failure.  

Testing for heartworm infections in cats is much harder to do than in dogs since cats are not the natural host for heartworms.  In order to diagnose heartworm in cats, multiple diagnostic tests are routinely used including bloodwork, x-rays, and echocardiography (looking at how the heart functions).

Though infections in cats can be light (consisting of just a couple worms), the importance of heartworms is amplified because even a small number of heartworms in a cat can be life threatening.  With the cat being an unnatural host for heartworms, the worms frequently move to other tissues of the body. This means we can find heartworms in other parts of the body such as the lungs, abdomen, blood vessels, and central nervous system in cats.  When the adult worms live in the lung blood vessels, they can cause a local inflammation of the vessels, but some cats never show signs of illness.  If cats do show signs, they are usually non-specific symptoms like wheezing or coughing.  Many respiratory diseases of the cat can cause these same symptoms which can be why heartworm disease is overlooked in cats.  As the worms live out their lives in the cat and start to die, the worms can cause inflammation of the lungs and become lodged in vessels which can lead to sudden death of the cat.  

OK, so now that we’ve reviewed heartworm disease in cats,  let’s get back to the question original question.    

“Does my indoor cat really need to be on heartworm prevention all year?”

The simple answer is YES!

Many cats live a more sheltered life than dogs, but unless the home provides an 100% effective barrier to mosquitoes , these “indoor” cats are also be at risk for heartworm infection.  In one study of heartworm disease in cats, approximately 25% of cats diagnosed with adult heartworms were considered indoor cats.  I’m sure we’ve all see a mosquito that has snuck into our home!

Administering a preventive year-round also has added benefits:

1) Activity against some common intestinal parasites (some that can infect humans!)

2) Stay in the habit (routines are hard to break!)

3) Work as a safeguard for missed doses (everyone’s human!).  

Preventives should be started in kittens at 8 weeks of age and be administered to all cats in heartworm endemic areas.  If you have any questions about heartworm disease or if you want to get your pet started on prevention, contact us today.  

Don’t leave your cats unprotected from this devastating disease!