Kenton Taylor, D.V.M.
cats, and ferrets. It is carried by mosquitoes and is most prevalent where
mosquitoes are abundant. Heartworm disease has become more common
throughout Northern California over the last fifteen years with the Sierra Nevada
foothills becoming one of the most heavily affected areas of the U.S.
The adult heartworm is large, up to 12” long, and lives predominantly in the
pulmonary arteries (pulmonary arteries carry blood from the heart to the lungs).
Infection causes the pulmonary arteries to become inflamed and thickened which
increases the work the heart must do to push blood past the worms to the lungs.
Signs of disease range from exercise intolerance and coughing to heart failure.
Therapy to kill the adult worm is available but is associated with mild to severe side
effects primarily due to the dead heartworms producing a severe reaction in the lungs.
Heartworm infection is clearly better to be prevented than treated. Prevention is best
begun at eight weeks of age. We currently recommend heartworm prevention for all
dogs traveling outside urban bay areas and for dogs living near or in the hills. There
are three choices available for prevention of heartworm disease.
Heartgard (Ivermectin) and Interceptor, Sentinel (milbemycin oxime) are chewable
tablets given monthly. Sentinel has the added advantage of controlling roundworm
and hookworm infections and it also contains lufenuron (Program) for non-insecticide
flea control.
Revolution (Selamectin) is a liquid applied to the skin on a monthly basis, which is
then absorbed into the body. Revolution is also effective against adult fleas, most
ticks, hookworms, roundworms, and ear and mange mites.
Your choice of heartworm prevention depends primarily on your choice for flea control
and also on convenience. Sentinel and Revolution have the advantage of controlling
fleas in addition to heartworm prevention. While the choices can be confusing our
veterinarians and staff can suggest the prevention best suited to your dog’s lifestyle
and your personal preference.
In California, heartworm preventatives are typically administered year round as the
hard frost season is short. Heartworm testing should be performed in all dogs older
than six months of age before instituting preventative. Yearly re-testing is not
recommended with year round preventative use unless you suspect a monthly
treatment was not given.
