Canine Heartworm

Brief Description

Canine heartworm is a vector-borne disease that affects domestic dogs, coyotes, black bears, and red and grey foxes. In the southeastern U.S., coyotes and domestic dogs are the most frequently affected.

Causative Agents

The canine heartworm is the nematode (roundworm) Dirofilaria immitis. The disease is passed from one animal to another through the bite of a mosquito.

Clinical Signs

Domestic dogs may have a chronic cough, low stamina, or respiratory distress when infected. Heavy infestations may lead to heart failure.


Heavy infestations can result in worms blocking and irritating the pulmonary artery, causing subsequent enlargement of the right side of the heart and decreased lung efficiency. Congestive heart failure may occur, leading to lung, liver, and kidney damage.


On necropsy, diagnosis is by through recovery of adult worms from the heart. In live animals, diagnosis is through an x-ray or a blood test; microfilariae (tiny worms) can be seen in a blood sample once the infestation is heavy enough.

Wildlife Management Significance

Coyotes can be stressed by heartworm infestation, and occasional mortality occurs; however, population-level effects are unlikely because coyotes usually do not show signs of the disease. Foxes and bears are very uncommon hosts of the disease. Based on the best information available, the most probably infection source for domestic dogs is other dogs, rather than coyotes.

Treatment and Control

Heartworm preventive medication is available for domestic dogs; this is the best control. Treatment of animals infected with heartworm is costly and dangerous, but is successfully done routinely. There is no control or treatment feasible to use on wildlife.

Public Health Implications

Occasionally, people have been diagnosed with a single heartworm in the lung; it is rarely found in the heart in humans. It does not generally cause disease symptoms in people and it’s occurrence is such a rare event that it is not a major public health concern.

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