Heartworms Are Forever!

By Ame Vanorio

What can be worse than worms inside your pet’s heart? Heartworm is a serious problem that affects cats, dogs, and ferrets. These worms literally invade your pet’s bloodstream and live inside the heart.

Heartworm is caused by the Dirofilaria immitis worm that lives in the heart, lungs and blood vessels of an infected animal. They look like spaghetti strands and the female worm can reach ten inches long. Heartworms can cause your pet to get very sick and even die.

Life Cycle

The worms are spread by mosquitos that carry infected larvae. As the mosquitos go from one pet to another they spread the disease. Once the larvae enter the body they travel in the bloodstream for six to seven months.

When the heartworm reaches adulthood it can remain in the heart for five to seven years. Both male and female worms are present and they can copulate, lay eggs and start the cycle all over.

A mosquito is needed to spread the disease. Your pets can not pass the parasite among themselves.

 Where is Heartworm Found?

Heartworm has been found in all 50 states, however, it is most common in states in the south and eastern coast.

The staff at Dr. Glaza’s clinic recently had a Lunch and Learn about heartworms. One of the things that we learned was that heartworm is spreading.

The American Heartworm Society states that heartworm cases increased by 21% between 2013 and 2016. They went on to say that environmental and climatic changes, a growing mosquito population, and the increase of wild dogs and coyotes are all factors.

Mosquitos are expanding their range northward due to the warming climate. This exposes more pets to diseases such as heartworms,

American Veterinarian
Heartworm is spreading https://capcvet.org/

How Does Your Veterinarian Test For Heartworms?

Testing for the parasite is quite simple and inexpensive. A small sample of blood is taken from your pet. The blood is then tested for antigens (heartworm proteins) or microfilariae (larvae).

Today’s tests are very accurate.

Testing must occur before the dog can receive preventative medicine. This is because most preventative medicines do not kill adult parasites. Giving your dog heartworm preventative if they already have adults in their system can harm your pet.

Dr. Glaza recommends testing every other year for all dogs on preventative. All dogs must be tested before they receive heartworm prevention.


Symptoms will differ based on the number of worms in your pet’s body. There are four stages or classes of infection.

  • Class 1:  A few mild symptoms such as an occasional cough.
  • Class 2:  More recognizable symptoms such as an occasional cough and tiredness after moderate activity. During this stage and more progressive stages, the heartworms will show signs that appear on an x-ray such as an enlarged heart.
  • Class 3:  Symptoms become more severe. You may notice your pet looks sickly, has a persistent cough, and gets tired easily.  Breathing problems and signs of heart failure are common.
  • Class 4:  This stage is called caval syndrome.  The blood flow is restricted by such a heavy worm burden that prevents blood from getting to the heart.  At this stage, the only way to treat the parasites is to remove the parasites with surgery. The surgery is risky, and most dogs with caval syndrome die. 

Prevention is Best!

Treating an active case of heartworms is expensive and very hard on your dog’s body. Treatment can cause blood clots and heart failure because when the worms die and decay they release toxins and segments into the body.

There are several types of heartworm prevention. All require a prescription from your veterinarian.

Monthly tablets and injections that last six months have been on the market for years. The problem with monthly prevention is that we forget to administer them. We get busy and before we realize we are two weeks off schedule.

Licking Valley Veterinary Services is now carrying a one-year injection called ProHeart 12. The great thing about this is that you don’t have to remember a monthly tablet. We will send you an email when your dog is due for their annual shot.

ProHeart 12 is an annual injection that prevents heartworms. Another advantage of this medicine is that it also kills hookworms.

Mosquito prevention can also reduce the risk and spread of the disease. Eliminating standing water around the home, encourage mosquito-eating wildlife such as bats and frogs, and keeping pets indoors during peak mosquito times can help reduce exposure.

Can Cats Get Heartworms?

Yes, both indoor and outdoor cats can get heartworms. It is not as common in cats as it is in dogs however one study showed an increase in cats.

Studies have shown that the parasite does not live as long on cats. About four years and the cat typically does not have such a heavy worm burden.

It is harder to detect heartworm infection in a cat because they are less likely to have the microfilariae appear in the bloodstream. This makes diagnosing more difficult and often the vet may have to rely on an X-Ray or ultrasound.

In addition, cats do not display as many symptoms as dogs do. Also, their symptoms, such as vomiting, decreased activity and appetite, and weight loss can be from a variety of cat problems.

Annual checkups and heartworm prevention medicine will help keep your cat healthy. Keeping your cat indoors will help lessen their exposure to mosquitos. Your cat can not catch heartworm from an infected dog or another cat.


The other pet that is susceptible to heartworms is the ferret. Like cats, ferrets may often be asymptomatic.

Symptoms of heartworms in ferrets include decreased activity level, coughing, trouble breathing, and overall weakness.

If you own a ferret you should talk to your vet about approved prevention for ferrets. At this time the FDA has only approved Advantage Multi for Cats in ferrets.

ProHeart 12 www.zoetisus.com

Author, Ame Vanorio, is the director of Fox Run Environmental Education Center and a licensed wildlife rehabilitator. She lives on her farm in Kentucky with too many animals to count! 

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