Heartworms: The 101

What are Heartworms? 

They are parasitic worms (Dirofilaria immitis) that inhabit the cardiovascular system of animals.  As adults, they reside in the right side of your dog’s heart and procreate.  Cats rarely have adult heartworms, but can be fatally affected by the damage caused by the juvenile parasites.

Which pets are at risk? Dogs and Cats.

How would my pet get Heartworms?

It takes the bite of one infected mosquito for the parasite to be transferred to an unprotected host.  With the increased prevalence of wild hosts (coyotes and foxes) in our suburban, even urban, areas the risk of Heartworm has increased… even in Northern states.  In Ohio, the mosquito continues to evolve into a hardier species, and our winter continues to shorten, making Heartworm prevention a year-round necessity.  Unfortunately, Cincinnati has ranked number one in the Nation for positive Heartworm test results.

How do I protect my pet? 

Dogs should begin prevention at 7 months of age, and then be tested at a year, then annually.  Unfortunately, prevention is not 100% if the pill is given late or is vomited or coughed up.  The test for dogs is a simple blood test and you can often receive the results the same day from your veterinarian.  If the test is positive, then additional tests will become necessary.  Your veterinarian will guide you through the treatment process at that time.  For cats, the test is a little more involved because they rarely have an adult parasite shedding proteins into the bloodstream.  Prevention in cats is even more important because of 1. There is no approved method of treatment for cats, and 2. In many cats, the only symptom of heartworm infestation is sudden death.

Is there a vaccination for Heartworm Disease? 

Not at this time, there are only prevention options.

What are some symptoms that my pet may be infected? 

In dogs: coughing, lethargy, labored breathing, decreased appetite and weight loss, dark or bloody stools may indicate Heartworm Disease.  In cats: vomiting, coughing, asthma, lethargy, loss of appetite and weight, or sudden death.

What are my prevention options? 

There are a few FDA approved prevention protocols for dogs and cats, in Pill, Spot-on and Injectable formulations.  Speak with your veterinarian about which protocol would be appropriate for your pet as some breeds have shown resistance and/or reactions to some forms of prevention.  At this time, there are no approved “natural remedies”.


My dog tested positive for Heartworm Disease, what now? 

Fortunately, this disease is very treatable:

  • Confirm the diagnosis. Once a dog tests positive on an antigen test, the diagnosis should be confirmed with an additional—and different—test. Because the treatment regimen for heartworm is both expensive and complex, your veterinarian will want to be absolutely sure that treatment is necessary.
  • Restrict exercise. This requirement might be difficult to adhere to, especially if your dog is accustomed to being active. But your dog’s normal physical activities must be restricted as soon as the diagnosis is confirmed because physical exertion increases the rate at which the heartworms cause damage in the heart and lungs. The more severe the symptoms, the less activity your dog should have.
  • Stabilize your dog’s disease. Before actual heartworm treatment can begin, your dog’s condition may need to be stabilized with appropriate therapy. In severe cases of heartworm disease, or when a dog has another serious condition, the process can take several months.
  • Administer treatment. Once your veterinarian has determined your dog is stable and ready for heartworm treatment, he or she will recommend a treatment protocol involving several steps. The American Heartworm Society has guidelines for developing this plan of attack. Dogs with no signs or mild signs of heartworm disease, such as cough or exercise intolerance, have a high success rate with treatment. More severe disease can also be successfully treated, but the possibility of complications is greater. The severity of heartworm disease does not always correlate with the severity of symptoms, and dogs with many worms may have few or no symptoms early in the course of the disease.
  • Test (and prevent) for success. Approximately 6 months after treatment is completed, your veterinarian will perform a heartworm test to confirm that all heartworms have been eliminated. To avoid the possibility of your dog contracting heartworm disease again, you will want to administer heartworm prevention year-round for the rest of his life.

My cat tested positive, what can I do?

  • Treatment, Unfortunately, there is no approved treatment for cats.  But because the parasite rarely grows to adulthood in cats, there can be spontaneous shedding of the parasite.  You and your vet can provide symptom support, aiding your cat’s recovery.
  • Monitor Due to the damage the parasite can inflict on your Cat’s lung function, you need to be aware of symptoms so that you and your vet can support your cat medically.
  • Prevention It is vital that you continue monthly prevention for your cat.  The cumulative affect of multiple infestations can be painful and, often, fatal.

Heartworm 101: Final Exam Cheat Sheet:  Test.  Prevent. Talk to your Vet.