The heartworms are transmitted by infected mosquitos, and once bitten, it takes about six to seven months for the heartworms to fully develop to the point at which they can be detected by a heartworm antigen test. Heartworms grow and intertwine, congregating within the right ventricle of the heart, hence their name. This can cause a significant blockage to blood flow, hence their deadliness.
To treat heartworm positive dogs, we start by placing them on doxycycline for 30 days, followed by the heartworm treatment – an intramuscular injection of an arsenic derivative. This causes the adult heartworms to die, and as they die, they are expelled into the dog’s bloodstream, so restricted activity is a must. If too many worms die at one time, they can clump together creating a clot-like effect, and restricted activity helps prevent this from happening. The more active a dog is that is undergoing treatment, the more risk of damage to heart and lungs. A month after the initial injection, there are two more injections given on two consecutive days, followed by another month of restricted activity. While the dog is likely heartworm-free at this point, we don’t recheck for six months to avoid getting a false positive result.
Treatment is very involved and much caution is needed to avoid creating more problems than the initial heartworm infection. Additionally, treatment costs run $400 to $500.
In the case of heartworms, an ounce of prevention is worth about a ton of cure! You should give your dog a heartworm preventative year-round, and yes, this means during the winter months even if there seems to be an absence of mosquito activity. It’s important to understand that the preventative doesn’t prevent an infection. It kills the immature parasites your dog may have contracted in the previous month.
If you’ve taken your dog off a heartworm preventative, you should definitely have your dog re-tested for the disease. If you resume using the preventative without re-testing, the preventative will kill immature worms in the bloodstream, but your dog may have more mature worms lurking, and only the actual heartworm treatment will kill the mature worms in the heart. Additionally, if your dog is diagnosed with heartworm disease, it is recommended that they be on the heartworm preventative throughout the entire treatment.
Heartworm preventatives are not that expensive, and there’s no reason not to give them year-round, no matter where you live.