heartworm diseaseBy now, most people are aware of the potential for catching a disease from a mosquito bite. Malaria, West Nile virus, and the rapidly spreading Zika virus all come to mind as reasons to do whatever we can to protect ourselves from mosquito bites.

Pets, too, can suffer from mosquito-borne illnesses. Although heartworm disease is arguably the most dangerous infection a pet can pick up from a mosquito, many pet owners are unaware of the risks.

What Is Heartworm Disease?

Heartworm disease is caused by a parasite, Dirofilaria immitis, which is transmitted by mosquitos. Over 70 different species of mosquitos carry the heartworm disease infection! The insect picks up heartworm parasites (also called microfilariae) by feeding on an infected animal, such as a dog, cat, coyote, raccoon, or opossum.

Once inside the host, microfilariae travel through the bloodstream where they eventually take up residence in the heart, lungs, and accompanying blood vessels. Over a period of several months to a year, the worms reproduce and grow, sometimes reaching up to 12 inches in length.

Mature heartworms cause much suffering and significant damage to a pet’s internal organs, and if left untreated, the pet will eventually die.


Heartworm treatment for dogs is possible as long as the disease is caught early enough. Unfortunately, it’s expensive, painful, and requires the dog to be confined, sometimes for months.

Unlike dogs, cats are not ideal hosts for the heartworm parasite. A cat’s immune system tends to respond aggressively to the presence of even one or two worms in the bloodstream, leading to severe symptoms, such as respiratory distress, blood clots in the lungs, and lung inflammation. Because there is not yet an approved treatment for heartworm in cats, the disease usually results in death.

Protection All Year Long

At Shelden Veterinary Care, we recommend annual heartworm testing and will prescribe the preventive medication that’s right for your pet. A monthly dose of a low-cost, oral preventive medication is all your pet needs to be protected from heartworm year-round.

Not only do these prescribed medications prevent heartworm, most also include medication designed to kill common intestinal parasites like roundworms, hookworms, whipworms, and tapeworms.

It’s common for pet owners to forgo monthly preventive medication in the winter, but we do not recommend this practice. It can take up to six months for a heartworm infection to become fully established. This means that if your pet is infected in September, for example, and you stop the preventive in October, the life cycle will continue on in your pet with no medication to stop its progress.

If you haven’t started your pet on a monthly heartworm preventive medication yet, or need a refill, please give the staff at Shelden Veterinary Care a call.