Heartworm is a long-lived parasite, with a life cycle that requires two hosts: the mosquito and the dog. Any dog that can be bitten by a mosquito is considered at risk. This means even dogs who spend most of their time indoors can be at risk for heartworm disease.
After the mosquito bites the dog, the immature heartworms enter the dog’s body and begin to grow. In a process that take approximately six months, they mature into adult worms and make their home in the blood vessels of the lungs and inside the heart.
The American Heartworm Society website has a video that shows the life cycle in depth. Just click on Life Cycle Video.
We cannot detect the immature forms of heartworm in a dog. That is why, in our seasonal climate, we recommend testing in the spring, to maximize the chance that we will detect an infection from last year as soon as possible.
Because heartworm infection can be fatal, we also recommend prevention.
The drugs that we use to prevent heartworm can be used at very low doses to kill the immature heartworms before they cause any illness in your dog. The medication in effect works ‘backwards’ to kill a new infection before the immatures can grow.
The most common prevention comes as a pill or a spot-on liquid that is used once a month through mosquito season. Be sure to give the final dose of the season even if you don’t see mosquitoes. We actually want that last dose to be applied AFTER the mosquitoes are gone, in order to be sure we prevent illness.
We have treated heartworm disease in dogs at Richmond Veterinary Clinic. We use higher doses of drugs with more potential for side effects, as well as the possible complications from parasites dying inside the blood vessels. It is a process that takes several months and requires the dog to rest for most of that time. Aside from the worry and expense, imagine having to keep your dog from running or getting excited for several months at a time.
Heartworm is an infection where prevention is really worth it.