Heartworm in Cats and Dogs: Don’t Let This Parasite Worm Its Way into Your Pet’s Heart or Lungs



A growing number of veterinarians are asking pet owners like you to protect their dogs and cats from heartworm disease instead of gambling that they won’t get it.

Pets get heartworm disease from mosquitoes that are infected with parasites. One bite can introduce parasites into your pet’s body. Once inside the body, the parasites nest and reproduce, lodging in your pet’s lungs and/or the right sides of his/her heart.

Heartworm has recently been diagnosed in about 30 species of animals in all 50 states, and affects millions of indoor and outdoor pets. To curb the rising number of cases, the American Heartworm Society (AHS) is asking pet owners to take a more proactive role in preventing the disease.

“We have all the tools to prevent it,” said Tom Nelson, DVM, owner of AAHA-accredited Animal Medical Center in Alabama and president of the AHS. “It’s really shameful that we have all of these positive cases.”
Part of the problem is lack of education.

New studies indicate that heartworm disease affects cats and dogs in all areas of the country, which is why veterinary experts suggest year-round prevention in all areas.

The American Heartworm Society and the Companion Animal Parasite Council recommend that all pets receive year-round heartworm protection so that pets are protected every month. It is critical that doses not be skipped or intervals between doses be extended because this results in an unprotected time during which animals may be exposed to heartworm larvae.

Pets should also have annual heartworm testing by a veterinarian prior to prescribing a heartworm medication.

Ask For More Information

Some veterinarians hesitate to offer prevention to their clients because they believe the disease is not a problem in their areas, but AHS statistics tell a different story.

A map of the United States, available on the AHS website, shows red splotches in areas where heartworm disease has been diagnosed. At quick glance, the varying shades of red make it look like the map is bleeding.
Because heartworm disease is no longer restricted to warm, humid areas, AHS experts suggest year-round preventative medication in all states and recently launched a campaign titled “KNOW More Heartworms” with the American Association of Feline Practitioners. This campaign targets cat owners.

One goal of the campaign is to dispel the myth that indoor cats are not at risk, said James Richards, DVM, a feline specialist who teaches at Cornell University in New York. One-half to one-third of the cats with heartworms do not go outdoors, he said.

Experts say that only 3.9 percent of cats in the United States are on heartworm prevention while about 50 percent of dogs are on preventative medication.

In Minnesota, where heartworm has been a significant problem for years, Pierce Fleming, DVM, recommends year-round prevention for dogs. And he recently started recommending it for all cats.

“Mosquitoes can get inside too,” said Fleming, owner of AAHA-accredited Plymouth Heights Hospital, who urges cat owners – with indoor and outdoor cats – to use heartworm prevention.

Know the Signs

The Food and Drug Administration (FDA) has not approved any drugs to treat heartworm disease in cats, which is why the AHS is focusing on prevention.

Clinical signs or symptoms in cats include vomiting, weight loss, diarrhea, coughing and difficulty breathing. Because cats tend to be couch potatoes, with limited opportunity for activity, it can be harder to identify breathing problems, which are often misdiagnosed as asthma. Pet owners may also mistakenly assume that low energy levels, a symptom of heartworms, are a sign of aging.

Three drugs have been approved by the FDA to help prevent heartworm disease in cats and dogs when given on a monthly basis. Several doctors also like the fact that preventive drugs also help protect pets from zoonotic diseases – like hookworm – that can be passed from pets to people.

Pamela Nichols, DVM, owner of AAHA-accredited Animal Care Center in Utah, says that heartworm prevention is simply good medicine. She advises clients to put their pets on preventive drugs because it protects them from heartworms and a slew of other parasites that can be transmitted from pets to people.
Some parasites – like roundworm – can cause blindness in children. Although it is very rare, it does happen, and it can be prevented.

“I have two clients that have vision in only one eye because of roundworm (parasite) infections,” Nichols said. “Anybody who wants evidence that this happens [can] look at these two families,” she added.

This article originally appeared in PetsMatter Volume 2 Issue 2, published by the American Animal Hospital Association. Copyright © 2009 AAHA.
Revised and updated Dec. 18, 2012.