• Chappelle Small Animal Hospital: Fort Collins Vet Services


Client Education Articles

Heartworm (Dirofilaria immitis)

Heartworm disease is transmitted by mosquitos. The infection used to be most prevalent in the southeastern United States. Today, however, heartworm is found throughout the country and continues to increase in incidence in Colorado. Heartworms are found in dogs, cats, ferrets and can also occur in wild animals such as foxes, coyotes and wolves.

The disease is spread when a mosquito bites an infected dog and then passes the infection on to other healthy dogs they bite. Once infected, developing heartworms migrate to the dog's heart and pulmonary vessels and can grow up to 14 inches long as they mature. If not removed with treatment they can cause permanent heart and lung damage and even death.

Most dogs with heartworm infection do not show signs of disease. Some vague symptoms may include decreased appetite, weight loss, and lethargy. Often, the first sign of the disease is a cough. Animals with severe heartworm disease will be exercise intolerant. Some dogs will look "pot-bellied" from fluid accumulating in their abdomen. Occasionally, dogs may have many adult worms, and can die of sudden heart failure.

Treatment for heartworm disease requires further diagnostic testing and can be serious and costly.

Heartworm disease can be easily prevented with medication. It is important, however, to test the dog’s blood for heartworms that could already be present before beginning preventative medication. A simple, yet very sensitive antigen blood test is performed to detect exposure to heartworm disease.

Who should be tested? We recommend all dogs over 6 months of age be tested for heartworm before beginning preventative medication. Then an annual test before prevention is started each season. If a dog is on year round medication and has not missed a dose, we still recommend yearly testing but the client may elect to test every other year. Puppies under 6 months can be started on the preventative immediately.

If the blood test is negative, the dog should be given a once a month tablet to prevent heartworm disease during the mosquito season of May through November in Fort Collins, CO.

Please call with any questions or you may walk in to our clinic for the heartworm test and preventative medication.