Ask the Vet: Heartworm Disease

Your veterinarian most likely recommends a heartworm preventative for your dog at your annual preventive care visit. So why the push? Why is heartworm prevention a key component of maintaining your pet’s health? If your pet is already on a heartworm prevention program—great job! If not, here are some specifics on heartworms and why giving your dog that monthly dose is important.

What is a heartworm infection?

Heartworms are a type of roundworm that looks similar to angel hair pasta. They live in the blood vessels around the heart and inside the heart itself. The worms cause a blockage of blood flow, leading to right-sided heart failure. When a dog has heart failure from heartworms, it will cough, breathe faster than normal, have a distended belly, and be unable to exercise. If left untreated, heartworm infections can be fatal.

How do dogs get heartworms?

Mosquitoes spread heartworms.  Once a carrier mosquito bites a dog, it takes six to seven months before adult worms live in the heart.  The adult heartworms then make baby heartworms, called microfilaria, which swim in the blood and can be picked up by a mosquito bite and spread to another animal.  Heartworm cannot be spread without going through a mosquito.

Can it be spread to people or cats?

Humans are rarely infected with heartworms.  The worms cannot complete their lifecycle in humans and become walled off as round nodules in the lungs.  Cats can get heartworm infections but are much more resistant than dogs.

How is it treated?

The treatment plan for an individual dog is based on the severity of the infection.  Typically, dogs are given a drug to kill the adult worms (Immiticide), antibiotics for secondary infections, and heartworm preventatives to kill the microfilaria.  After getting Immiticide, tiny chunks of dying worms are present in the lungs and can cause difficulty breathing.  Dogs must be kept calm, quiet, and rested for one to two months after getting the treatment to avoid side effects as their body breaks down the dying worms.

How is it prevented?

Multiple heartworm preventatives are on the market. These are safe and easily administered (usually chew or a topical ointment). Collies and other herding breeds can have negative side effects from the drug used in heartworm preventatives at high doses. The low doses of heartworm preventatives have been proven safe for all breeds.

How much heartworm disease do we see in the San Francisco East Bay?

Our clinic sees a handful of heartworm infections yearly; while it’s not a huge problem, it does occur. Heartworm disease is really common in the southern part of the United States. During a year with heavy mosquitoes, we could have an outbreak here in the Bay Area. Traveling with your dog could take him/her to areas much more infested with heartworms. Keeping your dog on monthly heartworm prevention is ideal for optimum health. These preventatives have the added benefit of being a general dewormer.

Talk to your veterinarian about which preventative is best for your dog.  Preventing a heartworm infection is much easier and safer than treating the disease. As Benjamin Franklin said, “An ounce of prevention is worth a pound of cure.” 

Use this link from the American Heartworm Society to learn about the heartworm life cycle, incident maps in your area, and much more: https://www.heartwormsociety.org/pet-owner-resources

Tags: Ask the Vet, Kristel Weaver, canine health, heartworm, pet health, dogs, cats, parasites, vaccines, vaccinations