There’s nowhere to hide from heartworm disease. This devastating parasitic infection has been identified in all 50 states, and affects more than a million pets. Fortunately, heartworm prevention is highly effective and can safeguard your pet and others from this potentially deadly condition. Providence Vet recommends year-round preventive administration and annual heartworm screening tests for dogs and cats. 

What is heartworm disease?

Heartworm disease is caused by an infectious parasite transmitted by a single mosquito bite. When an infected mosquito feeds on your pet, microscopic parasite larvae (i.e., Dirofilaria immitis) enter through the mosquito’s bite wound. Over the next several months, the larvae steadily migrate to your pet’s large lung and heart vessels, where they mature into adults that can grow 6 to 12 inches long. The mature adults reproduce and release a new generation of infective larvae (i.e., microfilariae) that enter the bloodstream. Another mosquito that bites will then pick up larvae and transmit them to other pets.

Adult worms cause inflammation and irritation to the heart and lung lining, leading to vessel thickening and dangerous—potentially fatal—blockages as the worms die off at various stages and are carried away through smaller arteries. 

Do cats get heartworm disease?

Cats are vulnerable to heartworm disease but are not the preferred host for this parasite, so an infection affects them differently. Only one to two adult worms are necessary to make cats clinically ill but, unfortunately, their subtle disease signs are commonly misdiagnosed as more familiar cat respiratory conditions. As the large worms die and form a vascular obstruction, sudden death may occur, and may be the first sign the cat was ill. 

Currently, no treatment is available for feline heartworm disease, making monthly prevention and annual testing vital for cats.

Are any other pets susceptible to heartworm disease?

Ferrets are highly susceptible to heartworm disease, and one or two adult worms can affect them similarly to cats. However, heartworm-positive ferrets exhibit signs similar to dogs, but no treatment is available, and a ferret-safe disease prevention product is necessary. Follow this link for more information about heartworm disease in ferrets. 

What are heartworm disease signs in pets?

Dogs will not show clinical signs until heartworm larvae have matured and begin to cause vascular inflammation. At that point, early signs in dogs may include:

  • Persistent cough
  • Exercise intolerance
  • Lethargy or fatigue

If the infection goes undiagnosed, thickened blood vessels and large adult worms cause resistance to blood flow, and increased demand on the heart and lungs. Then, additional signs may include:

  • Decreased appetite
  • Weight loss
  • Swollen abdomen 
  • Collapse
  • Heart failure

Ferrets experience similar signs, but with a more rapid onset because of their small size.

Heartworm-positive cats may be asymptomatic, experience respiratory difficulty that mirrors asthma or bronchitis, or a catastrophic blockage may result in sudden death.

How is heartworm disease diagnosed in pets?

Heartworm disease is diagnosed with a simple blood test designed to detect a protein (i.e., antigen) on adult female heartworms, or the presence of heartworm antibodies. If the pet tests heartworm-positive, they will be blood-tested again to check for microscopic larvae (i.e., microfilariae) that are more commonly found in dogs than cats. 

Because false positive tests occur, additional samples may be submitted to an external laboratory for review. Annual heartworm testing is strongly recommended for all dogs and cats, indoor and outdoor, to identify early infection and minimize long-term damage.

How is heartworm disease treated in pets?

Heartworm treatment, which is available only for dogs, involves a series of deep intramuscular injections to kill off circulating adult heartworms. If your dog is clinically ill, they will first be stabilized, to ensure they are healthy enough for treatment. All dogs must be activity restricted as soon as diagnosis is confirmed, to prevent excessive damage to the heart and lungs. The restriction is especially important during the treatment phase when the dead and dying worms can form a life-threatening blockage.

How can I protect my dog from heartworm disease?

Heartworm disease can be prevented only with prescription medication, typically administered monthly in oral or topical form, although long-term injectable medications are available for dogs. Heartworm preventives eliminate the circulating microfilariae, but do not kill adult heartworms, making heartworm disease testing prior to starting a prevention protocol essential. Your pet’s veterinarian will make specific product recommendations based on their species and health status, as well as your preferences. 

The heartworm test is a standard part of your pet’s yearly examination, and allows identification of early disease, so treatment or management can begin right away. 

Can I stop my pet’s heartworm prevention during the winter months?

While pausing preventives during colder weather may be tempting, this can leave pets vulnerable to infection. Infected mosquitoes can reemerge on mild days, or over-winter indoors in basements or garages, and heartworm prevention works retroactively, killing only the circulating microfilariae acquired over the previous 30 days. For the greatest peace of mind and protection, give heartworm preventives year-round.

Heartworm disease is an ever-present threat, but you can easily protect your pet with heartworm preventives, annual testing, and regular wellness care. If your pet isn’t currently on a heartworm prevention plan, schedule an examination and heartworm testing at Providence Vet, and let us customize a prevention program for your pet, and help ensure their good health.