According to the American Heartworm Society, Michigan veterinary clinics see up to 25 heartworm cases each year. In addition to infections in pet populations, the parasites also have been found in Michigan wildlife, including grey foxes, red foxes, wolves, and coyotes. Our team at Pierson Pet Hospital would like to educate you on this concerning disease, to help you protect your pet.

Infected mosquitoes transmit heartworms to your pet

When a mosquito takes a blood meal from an animal harboring heartworms, they ingest baby heartworms, called microfilariae, that become infective larvae over 10 to 14 days. After that time, when the mosquito bites another animal, the infective larvae are passed to that animal. Dogs, cats, and ferrets are the most common pets affected. 

  • Dogs — Once inside your dog, heartworms take six to seven months to travel through the bloodstream and mature to adulthood. The adult heartworms mate, the female heartworm releases her progeny into your dog’s bloodstream, and they travel to the heart. Heartworms can live five to seven years inside your dog’s heart, and the worm load can range up to 250 worms. Male worms grow to about four to six inches long, and females grow to about 10 to 12 inches.
  • Cats — Heartworms do not thrive as well inside a cat’s body. The worms reach adulthood in seven to eight months, rarely produce microfilariae in your cat’s bloodstream, and have only a two- to four-year life span inside cats. Most cats have only one to two worms, but they can still significantly damage your cat’s heart and lungs.
  • Ferrets — Your ferret is susceptible to heartworm infections, but they usually have a low worm load. Microfilariae are produced in only 50 to 60 percent of ferrets infected by heartworms.

Most pets initially exhibit no disease signs

Factors affecting heartworm disease severity include infection duration, and your pet’s worm load, activity level, and response to the parasites. Pets are affected in different ways.

  • Dogs — Heartworm disease has four stages in infected dogs.
    • Stage 1 — No signs or mild signs, such as an occasional cough
    • Stage 2 — Mild to moderate signs, such as an occasional cough, and fatigue after moderate activity
    • Stage 3 — More severe signs, such as a persistent cough, fatigue after mild activity, and an unhealthy appearance, with breathing difficulty and heart failure signs also common
    • Stage 4 — Also known as caval syndrome, the worm load is so high that the worms block blood flow back to the heart, requiring prompt surgical removal of the worms to prevent death
  • Cats — Many cats never show signs, and may die suddenly. Cats who do show signs usually exhibit nonspecific signs, such as vomiting, decreased appetite, and weight loss. Cats may also develop heartworm associated respiratory disease (HARD), which occurs when the microfilariae die, and cause a strong inflammatory response in the cat’s lungs. Signs include trouble breathing, increased respiratory rate, and cough.
  • Ferrets — Signs in ferrets are similar to those in cats, and include decreased activity, cough, trouble breathing, and weakness.

Heartworm disease diagnosis is easier in some pets

Our veterinary professionals at Pierson Pet Hospital use blood tests to diagnose heartworm disease in dogs. Five months after your dog is infected, the adult female heartworm begins producing certain proteins that can be detected with an antigen test. Another test detects antibodies against microfilariae in your dog’s bloodstream, which are produced by the adult female heartworm six months after your dog is infected. Your dog should be tested for heartworms at least once a year. 

Diagnosing heartworm disease in cats and ferrets is more complicated, because they are less likely to have an adult heartworm. Both tests are used, and if they indicate your cat or ferret is infected, an ultrasound or X-ray may be performed to verify a diagnosis.

Prevention is the best treatment for all pets

If your pet has heartworm disease, you must severely restrict their activity level, since an increased heart rate can result in sudden death. Dogs, cats, and ferrets require different treatment.

  • Dogs — Once your dog’s condition is stabilized, our veterinary professionals will devise an appropriate treatment protocol for them. Drugs used to kill heartworms are toxic and must be administered carefully, so your dog is not harmed. Treatment is painful, and typically takes months. Preventing heartworm disease by using regular heartworm preventives is a much better approach.
  • Cats — No medications are approved to treat heartworm disease in cats, making prevention the only way to protect your cat from this dangerous disease.
  • Ferrets — No medications are approved to treat heartworm disease in ferrets, so prevention is the only way to protect your ferret from the disease.

Several products are available that can be given monthly, every six months, or annually, to make protecting your pet convenient for your lifestyle.

If you are concerned that your pet has heartworm disease, or you would like to discuss heartworm prevention methods, do not hesitate to contact our team at Pierson Pet Hospital for immediate care, or to schedule an appointment.