Heartworm Disease

By Dr. Emily Hoppmann

Why are mosquitoes dangerous for dogs and cats? Mosquitoes are the most dangerous parasite for dogs, cats and other small mammals. This is due to the fact that this tiny little insect is the cause of a deadly disease – heartworms. Mosquitoes carry microscopic heartworm larvae and as soon as they start to feed on your pet, they leave the heartworm larvae behind to infect your pet. The larvae enter through the little hole that the mosquito left, enter the veins of the dog and over the next six months start to grow. The scariest part is that over the six months as they grow and find their way to the arteries of the lungs, you have no idea that your pet is even infected. Since heartworms are able to grow inside of your pet without you knowing that they are there, they are able to grow up to a foot in length in the arteries of the lungs before you start to see any clinical signs. This immediately causes severe inflammation in the lungs and heart which leads to congestive heart failure. In dogs, it is the number of heartworms that a pet has that dictates how severe the clinical signs are, how much damage is done to the heart and lungs, and how fast the disease progresses to heart failure. It is important to remember that as long as a dog is not on heartworm prevention, he will continue to get infected with more worms with every bite from a mosquito carrying the larvae. Heartworms can live happily in a dog for 6 to 8 years, reeking havoc on the heart and lungs the entire time. Eventually the worms die, but if left untreated it becomes a question as to whether the worms will die before they damage your pet so much that the disease becomes fatal. A lower number of heartworms in the early stages can cause very mild signs in dogs, such as coughing more or having a decreased energy level. The longer the infection is present and/or the more heartworms present the worse the clinical signs get. These signs include difficultly breathing, dizziness, and death. The best thing about heartworm disease is that it is totally preventable and if your dog does have heartworms it is treatable by a series of injections from your veterinarian. Untreated it is a fatal disease that can be expensive and sometimes risky to treat, but it never has to happen to your pet. One monthly pill from your veterinarian protects your dog from heartworms, so make sure your dog stays on monthly heartworm prevention and gets a yearly test from your veterinarian.

Mosquitoes enter cats the exact same way as they do in the dog and there have been hundreds of documented cases of indoor only and indoor/outdoor cats being infected with heartworms, so no cat is safe from this disease. We all have to face the fact that every time we open a door or crack a window, mosquitoes have a free pass into your home and access to your pets. Heartworm disease is almost worse in cats because cats are not the normal host. This means that there are fewer worms (usually 1 or 2) and they do not live as long (usually 2 to 3 years). That may seem like a good thing, but they actually cause more of a reaction in cats than in dogs, which means that even though they may spend less time in the cat, they cause more damage to the heart and lungs. What makes heartworm disease in cats even worse is that the worms are harder to detect since there are not as many and there is no treatment for cats once infected with heartworms. Some signs of heartworm disease include having trouble breathing or being more tired than usual. However, the scariest thing is that one of the most common signs of heartworm disease in cats is sudden death. The great news is that this is a totally preventable disease simply by applying a topical product, from your veterinarian, called Revolution to your cat every month.