Heartworm is a blood parasite transmitted by mosquitoes. The mosquitoes don't develop the disease themselves, they are just flying syringes passing the juvenile larval form of it from one dog to the next. Heartworm will gradually grow and multiply in the blood vessels adjacent to the heart, eventually leading to heart failure. The speed of this process varies a lot, but it averages around two years.
How Can We Prevent It?
There are a variety of safe and effective preventative medications. For most patients we recommend monthly Heartgard chewables, but a long-lasting injection (Proheart) and a topical oil (Revolution) are also available.
When Do We Give The Preventative Medications?
In Manitoba we recommend giving the first monthly dose around June 1 and the last around November 1. This may seem like we start late and go late, but this is because the medications prevent the disease from developing, they do not prevent the msoquitoes from biting or transmitting the parasite. The medications work by eliminating the juvenile larval stages of heartworm from the bloodstream, so they are used after exposure.
Do We Need To Test For Heartworm?
Maybe. The main reason to test is if your dog was not on prevention the previous season, or missed some of his medications. Do not rely on the fact that he seems healthy! During the couple years heartworm is growing in the system it often does not cause any symptoms. During this early stage it is still treatable, so it is important to identify it then. If your dog has always taken all of his heartworm preventatives as prescribed you should talk to your veterinarian about how often he still should be tested.