Five Myths & Misunderstandings
- Dogs vs. Cats
- Indoor vs. Outdoor Cats
- It's a Heart Disease
- Adult Heartworm vs. Larvae
1: Dogs vs. Cats
I thought heartworm was mainly a dog's disease.
Heartworm disease is not just a canine disease. Heartworms affect cats
differently than dogs, but the disease they cause is equally serious.
- Heartworm larvae induce an intense inflammatory response in the blood
vessels and tissues in the lungs.
- Once an adult worm dies, after 1-2 years, there is an additional intense
inflammatory reaction resulting in acute lung injury.
2: Indoor vs. Outdoor Cats
But my cat stays indoors, so she is safe, right?
It only takes one mosquito to infect a cat, and because mosquitoes can get
indoors, both indoor and outdoor cats are at risk and should receive heartworm
preventive medication. In a North Carolina study, 28 percent of the cats diagnosed
with heartworm were inside-only cats.
The severity of heartworm incidence as shown in this map is based on the
average number of cases per reporting clinic. Some remote regions of the
United States lack veterinary clinics, therefore we have no reported cases
from these areas.
3: It's a Heart Disease
How does it affect my cat?
The name "heartworm disease" is a misnomer, as the disease mostly affects the
lungs and not just the heart. Signs are often mistaken for feline asthma, allergic
bronchitis or other respiratory diseases.
In the x-ray, the cats lungs appear congested as a result of heartworm infection.
X-ray image courtesy of Dr. Ray Dillon, Auburn
University College of Veterinary Medicine.
4: Adult Heartworm vs. Larvae
What if the heartworm larvae never develop into adult worms?
Cats do not need an adult heartworm to exhibit clinical signs; in fact, larvae
are a main cause of the problems. Studies show 50 percent of cats infected with
heartworm larvae have significant disease of the small arteries supplying blood to the lungs.
Effect of Heartworm on Arterioles
A: An arteriole (small artery) in the lungs of a cat receiving heartworm preventive medication.
B: An arteriole from a cat infected with heartworm larvae, showing thickened walls which can cause complete obstruction.
Images courtesy of Dr. Ray Dillon and Dr. Byron L. Blagburn, Auburn University College of Veterinary Medicine.
Is it easy to test whether my cat has heartworm disease?
Diagnosis is difficult as negative antigen and antibody tests do not rule out
heartworm disease. Positive tests, however, are significant.