Heartworm disease in dogs and cats is very prevalent in our area. I run a large breed dog rescue and approximately 95% of the dogs I take into the rescue test positive for heartworms. This is a preventable disease. 

I have found that most people do not understand that a pill given monthly can prevent this disease. Prevention is much cheaper than the enormous costs of treating a dog once they have it. There is not a treatment for cats yet, just preventative.

American Heartworm Society

The Who, What, Where, When and Why of heartworms:

Heartworms are transmitted to your animals by mosquitoes. Once the animal has been bitten by an infected mosquito, tiny microfilaria grow into adult worms that set up shop in your animal's heart. You can prevent the microfilaria from growing into adults with a monthly preventative.

Dr. Stacey Hendershott from Pleasant Grove Animal Hospital says, "Twenty-five percent of cats that test positive for heartworms are "inside only" cats." Mosquitoes can find your pets where ever they are even if they stay inside all of the time.

When I bring a new dog into my dog rescue, I can usually tell by the dog's hair if it has some sort of worm infection. The coat is dull and coarse. A healthy dog usually has a shinny, full coat but that does not always mean a heartworm-free dog. (Food plays an important role in your dog's appearance as well as deworming on a monthly basis.) A seemingly healthy looking dog can be infected with heartworms. Prevention is key but there are also treatments available for dogs. You can pretty much count on the fact that if your animal is not on a monthly heartworm prevention, they will test positive. I suggest that you do some Internet research and then check with your vet to find out which prevention product and/or treatment will be best for you. Your pet's life depends on it.

There have been some cases of animals testing positive for heartworms even though a monthly prevention is given faithfully. It reaffirms the fact that you need to have your animals tested yearly to assure the prevention that you are using is effective. Don't wait until it is too late. Yes, this can be very expensive but the alternative can be horrible for you and your pet. Even though there is a treatment (for dogs only) it is very hard on the animal and it alters your daily life tremendously. I will explain why in a bit but first let's find out more about heartworms.

American Heartworm Society

Heartworm disease is in all 50 states but our region has a particularly heavy infection rate. We have more of a damp climate. Here is additional information from the American Heartworm Society:

How Heartworm Happens: The Life Cycle

First, adult female heartworms release their young, called microfilariae, into an animal's bloodstream. Then, mosquitoes become infected with microfilariae while taking blood meal from the infected animal. During the next 10 to 14 days, the microfilariae mature to the infective larval stage within the mosquito. After that, the mosquito bites another dog, cat or other susceptible animal, and the infective larvae enter through the bite wound. It then takes a little over 6 months for the infective larvae to mature into adult worms. In dogs, the worms may live for up to 7 years. Microfilariae cannot mature into adult heartworms without first passing through a mosquito.

What Are the Signs of Heartworm Disease?

For both dogs and cats, clinical signs of heartworm disease may not be recognized in the early stages, as the number of heartworms in an animal tends to accumulate gradually over a period of months and sometimes years and after repeated mosquito bites.

Recently infected dogs may exhibit no signs of the disease, while heavily infected dogs may eventually show clinical signs, including a mild, persistent cough, reluctance to move or exercise, fatigue after only moderate exercise, reduced appetite and weight loss.

Cats may exhibit clinical signs that are very non-specific, mimicking many other feline diseases. Chronic clinical signs include vomiting, gagging, difficulty or rapid breathing, lethargy and weight loss. Signs associated with the first stage of heartworm disease, when the heartworms enter a blood vessel and are carried to the pulmonary arteries, are often mistaken for feline asthma or allergic bronchitis, when in fact they are actually due to a syndrome newly defined as Heartworm Associated Respiratory Disease (HARD).

How Do You Detect Heartworm Disease?

Heartworm infection in apparently healthy animals is usually detected with blood tests for a heartworm substance called an "antigen" or microfilariae, although neither test is consistently positive until about seven months after infection has occurred.

Heartworm infection may also occasionally be detected through ultrasound and/or x-ray images of the heart and lungs, although these tests are usually used in animals already known to be infected.


Because heartworm disease is preventable, the AHS recommends that pet owners take steps now to talk to their veterinarian about how to best protect their pets from this dangerous disease. Heartworm prevention is safe, easy and inexpensive. While treatment for heartworm disease in dogs is possible, it is a complicated and expensive process, taking weeks for infected animals to recover. There is no effective treatment for heartworm disease in cats, so it is imperative that disease prevention measures be taken for cats.

There are a variety of options for preventing heartworm infection in both dogs and cats, including daily and monthly tablets and chewables, monthly topicals and a six-month injectable product available only for dogs. All of these methods are extremely effective, and when administered properly on a timely schedule, heartworm infection can be completely prevented. These medications interrupt heartworm development before adult worms reach the lungs and cause disease.

It is your responsibility to faithfully maintain the prevention program you have selected in consultation with your veterinarian.


Usually, all but the most advanced cases of heartworm disease can be successfully treated in dogs. Currently, there are no products in the United States approved for the treatment of heartworm infection in cats.

Once your dog has been treated for heartworms it is important that he remain calm and maintain a low-activity existence for approximately one month. This process will be no fun for you or your dog. I dread having to get a newly rescued dog treated because that means I am putting a large dog in a crate that is already experiencing anxiety from a change in location and usually has never been crated. Imagine the Tasmanian Devil cartoon character going wild. For the next two weeks I must take this newly relocated and just treated for heartworms dog on bathroom breaks on a leash then its back to the crate. Most of the newly rescued dogs do not know how to walk on a leash either. Prevention is key.