Heartworm Disease

Sheldon Rubin, DVM Past President American Heartworm Society

What is heartworm disease?
Heartworm disease, prevalent in all 50 states, is serious and potentially fatal, primarily affecting dogs, cats, and ferrets. Adult heartworms live in the heart and pulmonary (lung) arteries and can cause heart failure and severe lung disease.

How are heartworms transmitted?
Heartworm is transmitted by an infected mosquito, whose one bite can infect a dog or cat. It cannot be transmitted directly from animal to animal. When a mosquito bites an infected animal, it receives young heartworms (microfilariae) with the blood meal. After a short incubation period in the mosquito (10–14 days), heartworms can then be passed on to the next animal the mosquito bites. Larvae migrate through the tissues and enter the blood stream to the heart and pulmonary blood vessels where they can grow up to 12 inches and produce new microfilariae, beginning the cycle again.

My pet never goes outside—does she need heartworm prevention?
Mosquitoes enter homes all the time. All pets are recommended to be on preventives year round, regardless of where they reside.  Mosquitoes have been shown to survive winters inside homes and garages.

Can cats get heartworm disease?
Yes. Heartworm disease in cats is difficult to diagnose and a single worm can prove deadly.

How can I tell if my dog or cat has heartworm disease?
Your veterinarian will need to run blood tests and possibly chest x rays to determine if your pet has heartworm disease.  In later stages, as the heartworms mature, a dog may cough, become lethargic, have difficulty breathing, and lose stamina. Cats may develop vomiting, or coughing and breathing difficulties, resembling signs of feline asthma. Unfortunately, most cats will show no signs at all and pass away acutely from the disease.

Can infected pets be treated?
If detected early, heartworm disease in dogs can be treated. While the process is prolonged and can be expensive, the success rate can be high. Currently, there is no treatment for cats.

How is heartworm disease detected in dogs?
Your veterinarian must perform an annual blood test.  This is recommended even if your dog is on year-round prevention.

How is heartworm disease prevented?
Many safe, very affordable preventives are available by prescription from your veterinarian. With their proper and timely use, heartworm disease is 100% preventable.

Can heartworms infect humans?
This is very rare. Heartworms have been reported in the lungs of humans as nodules that are not easily distinguishable from lung cancer.