Heartworm Disease Explained

Posted In: Feline Health & Wellness, Canine Health & Wellness, Heartworm Disease

Heartworm disease is a serious and potentially fatal disease in pets caused by worms that live in the heart, lungs, and blood vessels. Heartworms can grow to be a foot long inside the body, causing severe lung disease, heart failure, and damage to other organs in the body.

Heartworm disease affects dogs, cats, and ferrets, but heartworms live in other mammals too, including wolves, coyotes, and foxes. Because foxes and coyotes live near human populated areas, they contribute to the ways heartworms are spread to pets.

Heartworm Transmission

Adult female heartworms living in an infected dog, fox, coyote, or wolf produce microscopic baby worms called microfilaria. The microfilaria circulate in the animal’s bloodstream. When a mosquito bites the infected animal and takes a blood meal, it picks up the baby worms. They develop and mature into “infective stage” larvae over a period of 10 to 14 days. Then, when the infected mosquito bites another dog, cat, or susceptible wild animal, the infective larvae are deposited onto the surface of the animal's skin and enter the new host through the mosquito’s bite wound. Once inside a new host, it takes approximately six months for the larvae to develop into mature adult heartworms.

Once mature, heartworms can live for five to seven years in dogs and up to two or three years in cats. Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.

Heartworm Disease in Dogs
Dogs are a natural host for heartworms. The heartworms that live inside the dog mature into adults, mate, and reproduce. If left untreated, the number of heartworms increase. Dogs have been known to have several hundred worms in their bodies!

Heartworm disease causes lasting damage to the heart, lungs, and arteries, and can affect the dog’s health and quality of life long after the parasites are gone.

Heartworm Disease in Cats
Cats, on the other hand, are an atypical host for heartworms. Most worms do not survive to the adult stage in cats. Cats typically have just one to three adult heartworms, and many cats affected by heartworms don’t have any adult worms at all. Because of this, heartworm disease often goes undiagnosed in cats.

Immature worms can cause a condition in cats known as heartworm associated respiratory disease (HARD). The medication used to treat heartworm infections in dogs cannot be used in cats, so prevention is the only way of protecting cats from heartworm disease.

Heartworm Disease in Ferrets
Heartworm disease in ferrets is a mix of the disease that we see in dogs and cats. Like dogs, ferrets are very susceptible to infection, and they can have large amount of worms. But like cats, a small number of worms, maybe even just one, can cause the disease because a ferret’s heart is so small.

Heartworm disease is more difficult to diagnose in ferrets, and there is no approved treatment. Prevention is necessary for all ferrets.

Heartworm Prevention
A consistent and year-round preventative is the best way to protect your pet. There are several options for preventative, such as a pill, topical medication, or injection. These work by eliminating the immature stages of the heartworm. Because it takes very little time for the larvae to reach a juvenile stage, heartworm prevention must be administered on a strict schedule in order to be effective. Your veterinarian will recommend the best preventative for your pet.

The Animal Medical Center of Mid-America has veterinarians at three locations that can answer questions about your pet’s health. Call 314-951-1534 or click here to request an appointment online.