- By: Stephanie Brittin, DVM
Tuesday, May 19, 2015
Heartworm: A Very Different Disease in Cats vs. Dogs
Both dogs and cats are susceptible to heartworm infection from mosquitos. However, the unique differences between each species means that heartworm disease in cats is very different than in dogs. Cats are not a natural host for the heartworm parasite, Dirofilaria immitis. So, when a cat is bitten by an infected mosquito, the cat’s immune system is able to kill most of the immature worms (microfilaria) before they reach adult life stages. Therefore, only a few worms usually reach adulthood in cats. Heartworms thrive in dogs, however, because dogs are a natural host of heartworm. A dog may have upwards of 50 worms inside him.
Unfortunately, it takes only one adult worm in a cat to cause clinical signs such as respiratory distress, coughing, vomiting, and even death. Furthermore, the immature worms and the cat’s own immune response to them can cause asthma-like lung disease with lifelong symptoms, known as Heartworm Associated Respiratory Disease (HARD). In dogs, it is usually only the adult worms that cause problems by damaging the heart and surrounding blood vessels. These dogs often develop a cough, which can progress to difficulty breathing, weight loss, and ultimately heart failure and death.
Heartworm is easily diagnosed in most dogs with a simple blood test which detects the presence of adult worms. Because infected cats usually only have 1 to 3 worms in their bodies, there are often too few worms for the blood tests to detect. Diagnosing heartworm infection in cats can be very challenging because false negative test results are common. When a dog is diagnosed with heartworm, there is an FDA-approved medication to eliminate heartworms. However, since there is NO approved treatment for heartworm infection in cats, the best we can do is try to manage the cat’s condition and symptoms. The good news is that heartworm is easily preventable in BOTH cats and dogs with year-round medication.