Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Heartworm Prevention Can Prevent Future Heartache


Pet Column for the week of March 29, 2004


Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Ann Marie Falk
Information Specialist

April showers bring not only May flowers but unfortunately mosquitoes as well. Pesky mosquitoes are the official airline of a blood-borne parasite that causes heartworm disease, a potentially deadly illness in dogs and cats.

"Heartworm disease is definitely easier and cheaper to prevent than to treat. Most heartworm preventatives are pills given once a month. If you're a forgetful sort of person, there is an injection that is given once every 6 months to prevent heartworm," explains Dr. Allan Paul, a veterinary parasitologist at the University of Illinois College of Veterinary Medicine in Urbana.

Heartworm's fancy name is Dirofilaria immitis, and the adult worms can reach over 12 inches in length. Mosquitoes pick up the immature worms (also known as microfilaria) when they bite an infected animal. When the mosquito bites another animal, heartworm is spread.

Spring begins the time animals are at risk of becoming infected with heartworm. The immature worms need to incubate for several weeks inside the mosquito and can only do this when the weather is nice. Once the weather has been nice for several weeks in a row, the danger of infection increases dramatically.

Heartworm, as its name implies, likes to set up house near and potentially in the heart. The adult worms sit mainly in the pulmonary artery-the blood vessel that carries blood from the heart to the lungs. The eventual result of an untreated heartworm infection is death due to heart failure.

"It's important to have your pet tested yearly for heartworm because sometimes signs do not develop for several years after infection. Treatment can be risky," warns Dr. Paul.

Animals with a heartworm infection will often have a cough and difficulty breathing. Fainting and fatigue are other signs that go along with a heartworm infection. As the infection progresses, symptoms of heart failure progressively worsen.

Once an animal has heartworm the treatment is aimed at killing the adult worms. This is accomplished by administering a form of arsenic in a dose deadly to the worms but not to the dog. The medication is not the dangerous part of treatment; the danger depends on the number of adult worms present. When large numbers of worms are killed at one time, widespread destruction of arteries can occur, along with severe lung damage.

"Cats are not as susceptible to heartworm as dogs. But where heartworm is very prevalent, for example, here in the Midwest, cats can become infected too. The theory is that cats are better able to fight off heartworm infection than dogs. On the flip side heartworm is harder to detect in cats," states Dr. Paul.

The number of adult heartworms in cats is much lower than in dogs. Cats have several adult heartworms at a time. Cats also mask their disease better than dogs. Signs may be non-existent or very generic. Within two years of infection many cats will die suddenly from heartworm disease. Especially if your cat is outdoors putting it on preventive medication may be a good idea.

Heartworm preventative is available at your veterinarian's office. Some of these medications also combat intestinal parasites as well.

Have your dog or cat heartworm tested. Contact your local veterinarian for an appointment to discuss the preventative that is right for you and your pet.