Heartworms are just what they sound like—long worms that live in the heart of our pets, other members of the dog family (coyotes, wolves), potentially ferrets, cats and even in very rare instances, humans. Heartworms are approximately 12 inches long—about as big as a long stand of spaghetti.
Our pets become infected with the worms when bitten by infected mosquitoes. Luckily, the Pacific Northwest doesn’t have as many infected mosquitoes as northern California, southern Oregon, Hawaii, the Mississippi River Valley and the Gulf Coast. Nevertheless, heartworm disease has been diagnosed in dogs in every state in the Union.
Part of the heartworm lifecycle must take place within mosquitoes. The remainder of the lifecycle takes place within infected dogs or other animals. Cats and people do not act as true hosts—that is they do not perpetuate the lifecycle. It takes about 6 months after the bite of an infected mosquito for the worm to reach the heart of a dog and become mature enough to continue the lifecycle. Each mosquito bite (from an infected mosquito) potentially can lead to a new heartworm in the dog. We don’t get a lot of mosquito bites! In some areas, a dog could get bitten many times in a single evening outside in its yard.
Heartworm infection is not a common problem in our area but it could become one. We have warm enough climates (our summers seem to be starting in May the last few years) and certainly enough moisture for mosquitoes. The biggest reason why it is likely to become more common is that we live in a mobile society. We take our pets with us when we travel—a week on Lake Shasta in a houseboat with his/her owners is enough for the pet to bring home an early infection, for instance. Even a trip to Boise, Idaho to visit family or friends, or to Cave Junction, Oregon can lead to problems! In addition, more and more shelters and rescue organizations ship dogs around the West and even around the country. Lastly, families in the armed services travel all over and they take their pets with them. Any pet with an unknown history should be tested—he/she could be infected.
Heartworm infection can lead to serious heart and lung disease. If there are enough worms in the heart, death is even possible. (Again, not common in this part of the country.)
Good news! There is a blood test to determine if our pet is infected long before it shows any signs of illness. That test is not expensive and can be done when you bring your pet in for their annual exam. Also, there are a number of effective heartworm preventives available from our office. Before starting a preventive, all dogs must test negative for heartworm infection. We stock several different kinds of heartworm prevention. Each preventive is either given orally once a month as a chewable tablet or beef-flavored chew or is applied to the skin/coat of your pet once a month. Lastly, if your pet is infected (the test is positive), there is a treatment for heartworm disease. Unfortunately, this is not an easy or inexpensive treatment. It is not like giving a ‘wormer’ for intestinal worms. There is only one drug approved to treat heartworm disease.
All in all, it is much better to start your puppy or your adult dog on heartworm prevention and give it year around than it is to hope that it never gets bitten by a mosquito. (It is not possible to test mosquitoes to see if they are infected.) This truly is “an ounce of prevention, is worth a pound of cure”. Please do not hesitate to ask your veterinary technician or Dr. Rinta, Dr. Johnson or Dr. Shattuck about this potentially serious, preventable disease.