Heartworm Disease in Cats

Heartworm affects cats too.  Largely thought of as a dog parasite, heartworm occurs in cats as well.  Moreover, 1 in 4 cats diagnosed with heartworm infection live indoors.

Heartworm is a worm that lives in the right side of the heart or pulmonary arteries in many species, including dogs, cats, ferrets, coyote, fox, wolves, and sea lions.  Some of the wild carriers of this parasite live and thrive in this region.

Cats are not a typical host of heartworm, therefore heartworm infection behaves differently in the cat.  While a dog could have more than 30 worms, a cat will generally have less than 3. Heartworms often do not mature to adults in cats, and because current tests evaluate for adult worms, infections in cats can go undiagnosed.  The early signs of heartworm infection in cats include coughing, asthma-like signs, vomiting, and poor appetite.  Over time, the worms die and send fragments to the lungs.  More serious signs such as collapse or sudden death can occur due to lung injury. 

The treatment that is used to effectively eliminate adult heartworm infections in dogs is not safe to use in our feline friends, underscoring the need for prevention.  Monthly preventatives are effective and highly recommended for cats.  An added benefit is that some also protect against fleas and intestinal parasites.  If infected, medications can be given to manage the signs that heartworm causes, but the cat is faced with the task of naturally clearing the parasite over time—usually 2 to 3 years.    

Our understanding of this parasite continues to evolve.  Cats, in their unique style, react to this infection in their own way.  We would expect nothing less of them. 

The American Heartworm Society Website has great information about heartworm in dogs and cats and was the source for the information contained in this article. 

https://www.heartwormsociety.org

article written by:

Laura Rau-Holl, DVM

Wolf Merrick Animal Hospital, Kenosha, WI

Heartworm in Dogs—the Big Picture

What is Heartworm?

Heartworm is a worm that is about the size of angel hair pasta that grow inside the right side of the heart and major blood vessels of the lungs.  Dogs, wild canids (fox, coyote, wolves), ferrets, cats, some other small mammals, sea lions and even very rarely people can become infected with heartworm.  Worms grow to adulthood most readily in dog and dog-like species.  Adult worms living in the heart will produce microfilaria (baby worms) that are transmitted via mosquito.  Adult worms can grow up to 12 inches long and live 5 – 7 years!

Heartworm disease refers to the illness caused by a heartworm infection.  Initially, an infected dog may have no signs of illness.  As heartworm progresses, damage to the lungs and heart will lead to cough, exercise intolerance, decreased appetite and weight loss, and ultimately heart failure.  Occasionally heartworm can contribute to kidney damage as well. 

The current recommendation of the American Heartworm Society, a veterinary organization that focuses on best way to contend with heartworm disease, is to keep pets on heartworm preventative all year around.  This recommendation is due to the many complex factors that contribute to the unpredictability and spread of this disease.  Prevention is safe, effective, and well tolerated.  

Important things to know:

1)  The mosquito is a necessary vector (carrier) for heartworm disease.  A very early stage of the heartworm development occurs in the mouthparts of the mosquito.

2)  Current tests can only detect adult heartworms living inside the heart. Following a bite from an infected mosquito, it takes 6 months for a heartworm (microscopic baby worm carried by the mosquito) to develop into an adult in the dog. 

3)  Heartworm has been diagnosed in all 50 states.  While transmission has not been documented in Alaska, there are brief times when this northern climate can support transfer of the disease. 

4)  Heartworm is on the move.  Some areas of the country have more heartworm than others.  The southeastern United States has consistently documented high infection rates.  Movement of dogs from these areas contributes to the spread of infection.

5)  “Heat islands” associated with buildings and parking lots of urban areas may extend active mosquito seasons and transmission of heartworm disease. 

6)  The course of treatment for heartworm disease takes many months.  In fact, dogs need to be restricted from activity for about 5 months during treatment due potentially severe lung embolism (clots) from dying worms. 

There are many great sources for pet owners about heartworm.  Here are some links to learn more:
 

The American Heartworm Society:    https://www.heartwormsociety.org/pet-owner-resources/heartworm-basics

The Companion Animal Parasite Council:  http://www.capcvet.org/capc-recommendations/canine-heartworm

The American Veterinary Medical Association:  https://www.avma.org/public/PetCare/Pages/Heartworm-Disease.aspx

Heartworm disease in cats manifests itself very differently and is deserving of a separate discussion. 

Sources:  The American Heartworm Society, the American Veterinary Medical Association, and the Companion Animal Parasite Council.

article written by:

Laura Rau-Holl, DVM

Wolf Merrick Animal Hospital, Kenosha, WI