Heartworms and canine heartworm disease are serious concerns, so make sure you know about the threat—and what to do about it—to help keep your assistance dog safe and healthy.
What Are Heartworms?
Heartworms are parasites that live in a host’s heart, lungs, and connected blood vessels, growing to up to 14 inches in length. They favor domestic and wild dogs, but do infect other animals, like cats, ferrets, sea lions, and, on rare occasions, humans. Heartworms are found everywhere in the U.S., but infections are most common along the East and Gulf Coasts and the Mississippi River.
What Is Canine Heartworm Disease?
Heartworms cause the potentially fatal heartworm disease in their hosts primarily by feeding off them, obstructing blood flow in and out of the heart, and interfering with the heart valve’s normal operation. Left unchecked, major organs do not receive an adequate blood supply and increasingly malfunction and begin to fail.
How Are Heartworms Transmitted to Dogs?
Mosquitos pick up microscopic baby heartworms called microfilariae when they feed on the blood of an infected animal. These mature into larvae in the mosquito for 10 to 14. Then, when the mosquito bites another animal, the larvae are deposited into the new host. The success rate is quite high in dogs, with almost 100 percent of those exposed becoming infected. In the host, heartworms mature for about 6 months into adults and live for 5 to 7 years, causing serious internal damage and reproducing.
This is the only way heartworms are transmitted, and mosquitoes are the only known carriers of infective heartworm larvae. These parasites aren’t contagious; infected animals can’t spread them to other animals.
What Are the Signs and Symptoms of Heartworm Disease in Dogs?
Individual factors affect how quickly and severely signs and symptoms manifest, including a dog’s age, activity level, and general health; how many worms are residing in the dog, which is known as the “worm burden;” and how long the infection has existed.
Early on, there aren’t usually noticeable signs or symptoms. The first symptom is often a mild occasional or persistent cough. Other common signs of beginning heartworm disease include fatigue or tiring easily, reluctance to exercise, loss of appetite, and weight loss.
As heartworm disease progresses, its effects become more obvious and the danger ever more significant. Common signs and symptoms include a worsening cough, deteriorating body condition, difficulty breathing, abdominal swelling, and heart failure.
How Are Dogs Tested for Heartworms?
In general, dogs should be tested annually for heartworms, though there are reasons your veterinarian might recommend more frequent testing or specific timing. Testing is most commonly done with a blood test called an antigen test. Another blood test can detect microfilariae in the bloodstream, which indicates the presence of adult heartworms.
How Are Heartworms Treated in Dogs?
Usually, infected dogs can be treated successfully. If your service dog is confirmed to have heartworms, immediate exercise restrictions will be put in place. Your vet will determine when your dog is stable enough to proceed with treatment (in rare cases of advanced heartworm disease and significant organ failure, this may not be possible). An injectable drug kills the heartworms. There is also an injectable drug that kills microfilariae in the bloodstream. Additional therapies may be needed to manage symptoms and organ damage from heartworm disease.
How Is Canine Heartworm Infection and Disease Prevented?
Because heartworms and heartworm disease are so serious, and because treatment is expensive and hard on dogs, prevention is essential. There are numerous FDA-approved prescription canine heartworm preventatives available, most of which are easily administered topically or orally once per month. Ask your vet for a product recommendation and about an appropriate administration schedule.
Though we don’t endorse any specific brand name medications here is an informative link to a Doctors Foster & Smith article page showing a Heartworm Preventive Products Comparison Chart.