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Heartworm Disease….Everything You Need To Know To Keep Your Pets Safe!

Heartworm disease is a very serious and potentially fatal disease that is transmitted by mosquitoes. As a small animal veterinarian practicing in South Florida, I sadly diagnose heartworm disease all year long, and am all too familiar with the severity and consequences of heartworm disease.  Many parts of the country that experience colder weather during fall and winter seasons have a significant decline in mosquito population; and, therefore there is less risk of infection to dogs and cats in those areas.  Regardless of where you live, monthly heartworm prevention is safe, easy, and crucial in preventing this disease.  Today I am going to discuss some of the key aspects of heartworm disease, and most importantly, how we can keep our pets living long healthy lives free of heartworm disease.

What Is Heartworm Disease?

Heartworm disease is a parasitic disease that is transmitted to dogs and cats by infected mosquitoes. Once infected, the parasites grow and develop into foot-long worms that live in the heart, lungs, and vessels. Heartworm disease can cause severe lung disease, heart failure, and damage to other organs in the body.

What Animals Can Be Infected With Heartworm Disease?

Heartworm disease affects dogs, cats, wolves, coyotes, foxes, sea lions, ferrets, and in rare instances, even humans. Dogs are a natural host for heartworms, which means once the dog becomes infected; the heartworms can mature and produce offspring, sometimes up to several hundred worms, while living in the host. Cats can become infected with heartworm disease as well, but they are an atypical host for this parasite. Most of the parasites in a cat do not survive to the adult stages, so a cat may be infected with one to three worms, while a dog can be infected with several hundred. Still, cats can endure severe damage from the immature worms and develop heartworm associated respiratory disease (HARD), similar to dogs. Unfortunately, the medication used to treat heartworm cannot be used in cats, so prevention is the only way to protect your cat from heartworm disease.

How Does My Pet Become Infected With Heartworm Disease?

Mosquitos play an essential role in maintaining and spreading heartworm disease. Mosquitos transmit the disease by feeding on infected animals, and picking up “baby worms” which then develop into larvae in the mosquito within 10 to 14 days.  When an infected mosquito bites and takes a blood meal from an animal, it deposits infected heartworm larvae into the animal and the animal becomes infected with heartworm disease.

What Are The Clinical Signs of Heartworm Disease?


Early Stages of heartworm disease

  • No symptoms at all- please take note!
  • Mild persistent cough
  • Reluctance to exercise
  • Fatigue, especially after exercise
  • Decreased appetite
  • Weight loss

Later more advanced stages of heartworm disease

  • Heart failure
  • Swollen belly
  • Caval syndrome (sudden blockage of blood flow to the heart) which causes labored breathing, pale gums, and dark bloody coffee colored urine.


  • No symptoms at all!
  • Coughing
  • Asthma-like attacks
  • Periodic vomiting
  • Lack of appetite
  • Weight loss
  • Difficulty walking
  • Fainting
  • Seizures
  • Sudden collapse


How Do I Test My Pet For Heartworm Disease and How Often Should I Have Them Tested?

As a small animal veterinarian practicing in South Florida, mosquitoes are present all year. The risk of pets becoming infected in warmer climates where mosquitos thrive is far greater than in places with cooler fall and winter seasons.  I require that all my patients be tested for heartworm disease one time per year to ensure that all preventions are working effectively.  Even when my patients are on consistent monthly heartworm prevention, it is imperative to test yearly.   Heartworm preventatives are highly effective, but there are pets that can become infected despite preventatives.  Despite where you live, yearly testing is the general guideline for all veterinarians and recommended by the American Association of Heartworm Disease.  The test requires a small drop of blood and is processed within in 10 minutes in the hospital.  Some veterinarian may send the test out to a diagnostic laboratory.

Is There A Treatment For Heartworm Disease?

For most dogs, if they become infected with heartworm disease, there is a treatment.   If the disease is not too far advanced and your pet can endure treatment, your pet can be treated for the disease. Treatment options normally involve a strenuous and complex 3-month regimen with restricted exercise, heartworm prevention, antibiotics, steroids, if needed, and injections of immiticide to kill the adult worms.  The treatment is costly and straining on the dogs. Often times, they become ill from the side effects of the treatment.

Unfortunately there is no approved treatment for heartworm infection in cats, and the drug that is used to treat dogs is not safe for cats. If your cat is diagnosed with heartworm disease, our goal as veterinarians is to stabilize, and manage the disease. On occasion, cats can spontaneously clear the heartworms from their systems; however, the damage left by the heartworms can be permanent. Many times, depending upon the severity of the clinical signs, the disease and the symptoms can be treated to maintain long-term health.

How Can I Protect My Pet Against Heartworm Disease?

I cannot stress enough the importance of monthly heartworm prevention for both cats and dogs. Heartworm preventatives are inexpensive, easy to administer, and are very safe. Heartworm disease is an extremely serious, progressive, and sometimes fatal disease.   As mentioned above, there is no approved treatment for heartworm disease in cats.  Treatment options for dogs are costly and, more importantly, strenuous on a dog’s body.  Heartworm disease can result in permanent damage to the heart, lungs, arteries, and can affect your pet’s health and quality of life long after the parasites have been treated and are gone. For this reason alone, prevention is by far the best option to keep your pets safe, healthy and happy.

I hope this article was helpful and learning about heartworm disease and how to keep your pet safe from this disease. The earlier the disease is detected, the better the chances are your pet can be treated and not suffer from long term effects.  Yearly testing and monthly preventatives are crucial in the spread and prevention of heartworm disease.  As always, my goal is keeping our pets living long, happy, and healthy disease free lives.  I much prefer providing preventative care to my patients rather than treating disease.





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  1. This is very helpful and educational information..I knew very little about heart worm disease and knowing how often I should have my pup tested helps! Thank you