The Vet and Rehab Center of Cape Elizabeth

207 Ocean House Road
Cape Elizabeth, ME 04107



Ask the Vet About Heartworm


Ginger Browne Johnson DVM, CCRP, veterinarian in Cape Elizabeth, Maine, Ask the Vet blog, Heartworm treatment and preventionAmong the many dangers to our pets, a silent killer is starting to re-emerge in the Northeast. Once considered almost eradicated in this region, Heartworm has become a renewed threat to pets in Maine. It is also one of the most misunderstood by pet owners.


We are seeing and treating many more cases of heartworm positive dogs these days, and they come to us from all different circumstances, from newly rescued dogs to older family dogs, and always well loved and cared for. But it only takes one mosquito bite in an unprotected moment to transmit this devastating disease from one dog to another.


So, what IS heartworm? Heartworms grow from 4 to 12 inches long and live in the heart, lungs and associated blood vessels of affected pets, causing severe lung disease, heart failure and damage to other organs in the body. It is spread by mosquitoes who deliver the microfilaria directly into the bloodstream, where they mature into larvae and ultimately worms.



Some of the most frequently asked questions we get about heartworm stem from misconceptions about preventatives and testing:


If I give heartworm pills every month, why do I still have to test every year?

Most owners are surprised to learn that our dogs get infected all the time, and the heartworm pills that you give once a month kill the larvae already present. Because of this, if your dog vomits up a pill while they are out of your sight, or if they don’t chew the pill enough, or if you simply forget to give the pill one month, then they are not protected. And once the larvae reach the worm stage, heartworm pills will no longer be able to kill them. Although it is important to continue giving the pills every month to get rid of any new larvae produced by the infection, the only way to detect adult worms is by testing every year.


What should I do if I miss a dose one month?

Notify your veterinarian if you missed giving a dose. If it’s at all possible that you missed two doses, then you should get your pet tested in six months. It takes six months for the larvae to show up as a positive on the antigen test. The earlier it is detected, the better the chances the pet will recover.


Treatment is long (a series of treatments are administered at your vet’s office over a period of weeks, during which the patient must be kept very quiet - not even any walks), dangerous (the medications used can cause severe adverse reactions), and costly (cost is related to size of dog). Luckily the monthly preventatives are inexpensive and easy to administer!


Can cats get heartworm?

Yes. Prevention for cats is a monthly topical medication that also protects them from fleas and other parasites. Unfortunately, there is no approved drug therapy for heartworm infection in cats, and the drug used to treat infections in dogs is not safe for cats. Nevertheless, cats with heartworm disease can often be helped with good veterinary care.


Why is heartworm disease increasing in the area?

We are not really sure. Certainly we are adopting more dogs from the south, and many of them arrive already heartworm positive, which would be introducing the disease back into the area. Foxes, coyotes and other wildlife can also carry heartworm. But lack of testing and not giving preventatives correctly contribute directly to the spread of the parasite.


Why do I need to give heartworm pills year around if it is spread by mosquitos?

 The Heartworm pills that you give every month will kill the larvae in the bloodstream, so if your pet has contracted heartworm, the pills will kill off larvae produced by the adult worms, thus increasing the chances that your pet will survive until treatment.

Written by Robin Elliott


Send your questions to:

Dr. Ginger Browne Johnson  |  Veterinary and Rehabilitation Center of Cape Elizabeth

EMAIL - (attn: Ask the Vet)