When is a mosquito bite more than just an itchy annoyance for your dog, cat, or ferret? When that mosquito is carrying a parasite called heartworm (Dirofilaria immitis). Found in all 50 states but most prevalent in the South and Midwest, heartworms are transmitted from one pet to the next by a mosquito.
Heartworms start as tiny microfilaria that can only be seen under a microscope. Over the next 6 months they lodge in the vessels of the heart and lungs and grow to be over a foot long. Adult heartworms can live in your pet for up to 7 years, and create thousands of baby heartworms that will be transmitted to other pets through new mosquitoes.
Heartworm disease is the syndrome caused by these worms living inside your pet. At the beginning, your dog will not show any signs of illness. Early signs of illness can include decreased activity, decreased appetite, weight loss, and/or mild cough. Over time, the heartworms can cause heart failure, kidney failure, or sudden death. Cats and ferrets can get severe disease from just a couple worms, and unfortunately there is no treatment for heartworm in these pets.
Dogs can be treated for heartworms with a medication called immiticide. This kills the adult heartworms and then your dog's immune system will gradually break down the worms. Treating heartworm is a very time-consuming and expensive process. It must be done gradually, because the dead worms can cause potentially fatal clots. Your dog is absolutely NOT allowed to run during the months of treatment because exercise can dislodge a worm and cause sudden death. In order to decrease this risk, we start with a month of an antibiotic to weaken the worms prior to the immiticide and steroids to decrease the inflammation in the lungs following the American Heartworm Society Guidelines.
So, that's all the bad news. What's the good news?
The good news is that heartworm disease is completely preventable. There are many preventive medications available that stop the baby heartworms from developing into adult disease-causing worms. Adding in mosquito repellent provides another layer of protection.