Heartworm disease develops when a dog is bitten by a mosquito carrying microscopic larvae of parasites called Dirofilaria immitis. As a mosquito feeds, these microscopic larvae infect and begin their migration into the dog's bloodstream, where they grow into adult worms. They make their home in the right side of the heart and vessels of the lung (pulmonary arteries), often causing lung disease and heart failure.
The risk of infection varies from one region of the country to another. Heartworm has not established itself as a self-sustaining disease in Central Oregon, and our current climatic conditions may be prohibitive to the mosquito vector that transmits the disease. But, infected dogs from other areas have been diagnosed and treated here. Circumstantial evidence of local transmission in the La Pine/Sunriver areas points to the possibility that a dog in the wrong place at the wrong time may result in infection. We advise that dogs living or spending time in these areas or other mosquito infested areas of Central Oregon, particularly areas frequented by tourists, be treated monthly with heartworm preventive medication. Dogs traveling out of Central Oregon should also receive treatment for a minimum of two months after exposure is over. In complying with manufacturer’s recommendations, we advise testing prior to initiating or restarting any heartworm prevention as administration of preventives can cause life-threatening reactions when given to heartworm-infected dogs.