Heartworm is a potentially deadly parasite that primarily infects dogs, cats, and ferrets. There have been documented cases of heartworms in people, but it is very rare and results in no signs of illness.
Heartworms are transmitted through the bite of an infected mosquito. When a mosquito bites an infected animal, young heartworms called microfilariae enter into the mosquito. Microfilariae develop into infective larvae inside the mosquito. The infected mosquito may then bite another animal and transmit the disease to that animal. It takes around 6 months for infective larvae to mature into adult heartworms. These worms usually reside in the heart or blood vessels of the lungs. Female heartworms can be up to 14 inches long! These worms cause damage to the blood vessels and affect the heart’s ability to pump blood resulting in severe heart and lung disease which may result in death.
Early in the course of disease in dogs, your pet will likely show no symptoms, but as the disease progresses, you may notice exercise intolerance, lethargy, coughing, or difficult breathing. Signs of heartworm disease in cats include coughing, respiratory distress, and vomiting. In rare cases, cats may suddenly die from heartworms with no apparent symptoms.
Diagnosis of heartworm disease may be made by simple blood tests which detect the antigen of the female adult heartworm. After diagnosis with this test, further tests such as chest x-rays and a blood profile are usually performed to determine the severity of disease before deciding the best protocol for treatment. In cats, the diagnosis can be trickier and may require both an antigen and antibody test.
The best way to treat heartworms is to prevent them with FDA approved heartworm preventives. The preventives will not kill adult heartworms, but rather the microfilarial stage. Therefore, a heartworm test is recommended before placing your pet on a heartworm preventive medication. Heartworm testing should then be performed periodically, usually yearly, to make sure your pet has not contracted the disease. There have been cases of heartworm disease in animals on heartworm prevention, so it is very important to occasionally test your pet. Additionally, it is very important to follow label directions on heartworm preventive drugs. If your dog tests positive for heartworms, there is an FDA approved drug to treat heartworms. While your dog is treated, it will require complete rest as these adult heartworms are killed. There is currently no effective and safe treatment for heartworm disease in cats. If positive, cats may be treated with medications to reduce the inflammatory response associated with heartworm disease. Occasionally, surgery is performed to remove adult heartworms in severe cases.