Heartworm Disease

How to recognize it, How to prevent it, How it’s treated.



What are the symptoms of heartworms and is there a cure? If I give my dog a heartworm pill every month, do I have to give him wormer medicine too?


Dr. Nichol:

Smart questions. Every dog owner hears recommendations of heartworm prevention. But not everyone knows why. I’m a veritable fountain of information so I will enlighten you.


Dirofilaria immitus (impressive name, eh?) is a stringy, spaghetti-like worm that gets biggest in the heart but does its worst damage in the lungs. Occasionally other organs like the kidneys, liver, brain, and eyeballs are also affected. Most infected dogs cough on exertion, lose weight, and become much less active. The reason is that worms living in the vessels of the lungs choke off the blood supply. Badly infected dogs cough up blood. Some arrive at the animal hospital in acute liver failure. Cats, too, can get heartworm. And it is treatable. An injectable called Immitacide works well but severe infections result in permanent lung scarring-meaning a lot less stamina. Without treatment many cases are fatal.


That all sounds awful but it’s also unnecessary because the preventives, Heartgard Plus and Interceptor, are very good. Use either of them-whichever your veterinarian recommends. They also prevent two intestinal parasites so you shouldn’t need other wormers. Given monthly they work against heartworm by killing the microscopic larval worms that pets get from carrier mosquitoes.


One last point: Mosquitoes have gotten better adapted-they can now live inside homes in the winter. So give the chewable tablets once monthly-year ’round. Don’t stop in the fall. But while the preventives are good, they’re not perfect. So get a heartworm blood test once a year for safety-just in case. And don’t believe that thick-coated dogs are safe from marauding bloodthirsty mosquitoes. We see more heartworm infections in all breeds every year.