What You Should Know About Heartworms In Dogs | Heartworm Disease

Although heartworm infection in dogs can be found anywhere mosquitos are common, most cases are found within 150 miles of the U.S. coastal regions from New Jersey to Texas, along the Mississippi Rivers and its tributaries. The American Veterinary Medical Association estimates that approximately 25% of all dogs in this country carry the disease – a problem that is easy to prevent and difficult to treat.

Here we listen to a short discussion by animal veterinarian, Dr. Sam Meisler, DVM, about how to treat and how to prevent heartworm disease in dogs:

Mosquitos transmit canine heartworms from dog to dog. When a female mosquito bites an infected dog, the larvae of the heartworm – called microfilaria– contaminate the mosquito’s saliva and are drawn into the body of the pest. The microfilariae develop within 2 to 21/2 weeks in the body of the mosquito, and are then injected into the skin of another dog, where, after another 100 days, the progress into the bloodstream. The larvae receive nutrients from your dog’s blood and continue to grow, eventually settling in the animal’s blood vessels.

As the larvae grow to full maturity, they can reach several inches in length and will, eventually, migrate to your pet’s pulmonary artery where they mature into adults. Once there, heartworms cause extensive damage — weakening the lining of the artery, increasing blood pressure, and causing right-sided heart enlargement that leads to cardiac dysfunction and disease.

Heartworm Symptoms slow to start showing

Your dog may not show any symptoms at all until the disease is far advanced. It normally takes 7 years from inception for heartworm larva in the artery to grow to a size to create problems. Animals with this parasite normally show all the signs of a dog with advanced heart disease. They will present with exercise intolerance, may start coughing after exertion, and may be susceptible to lung problems. Often, severely sick dogs will show extended bellies from fluid build-up, can cough up blood, and may be anorexic – unable or refusing to eat. Eventually, without treatment, the heart will be unable to function at all and your pet may die.

Heartworm Diagnosis and Treatment

Your veterinarian diagnoses heartworms in an animal in several ways. The first way is to take a small drop of blood, and place it under a microscope. In some instances, if the microfilariae are large enough, a trained technician or vet can see them moving in the blood serum.

The second way is called a “snap” test. A small drop of blood is mixed with an anti-coagulant then dropped onto a reagent strip in a small, “snap” canister. The canister is snapped closed, releasing the reagent to mix with the blood, and within one minute, the reagent reacts to the specific heartworm antibodies in the blood of your dog if it is infected.

Another diagnostic test requires the blood to be filtered through fine mesh, removing the microfilaria and/or larger worms, which can then be seen under a microscope.

Treatment of canine heartworm disease involves injecting your pet with melarsamine dihydrochloride – trade name Immiticide – in the lower muscles of the back twice, each injection being 24 hours apart. This kills the adult worms that then disintegrate and pass out of the dog’s body. During this time, usually a period of around 6 weeks, it is extremely important that you keep your dog quiet and disallow any exercise. As the adult heartworms die, they can damage the heart muscle if your dog becomes too active.

How Can You Prevent Your Dog from Heartworm Disease?

Prevention of heartworm disease revolves around daily or monthly doses of either diethylcarbamazine (DEC) or ivermectin in easily chewable pills or treat form. Your veterinarian can sell them to you or give you a prescription to get the drugs online.

Remember, if mosquitos are in your backyard, they can get into your house; so housebound pets are just as vulnerable to this disease as those dogs that live outside.

Male dogs seem to contract the disease more than females and large-breed dogs are more susceptible than small-breeds, probably because they are outside more often. Infections are normally found when dogs are between 3 and 8 years old, but your dog should be checked yearly for microfilaria. Puppies do not need to be tested before the age of 6 months because the larvae are not large enough until that age to show up on screenings


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