Summer 2011 Magazine

Casa Canine

Parasitic Worms in Dogs: Part 2:
Heartworms and Tapeworms

By Deborah Schildkraut, Ph.D.

Heartworms and tapeworms are two common parasites that may take up residence inside your dog. Heartworms are a potentially lethal threat to dogs, yet easily controlled with preventive medication. Tapeworms are nasty and annoying worms that are most often treated only after an infestation is noticed. How do these worms find their way into your dog? How do they affect your dog's health? What are the treatments for these worms? And what can you do to keep your dog healthy and worm-free?

Heartworms: The jar sits on the reception counter at my veterinarian's office. Inside the jar, a dog's heart floats in formaldehyde, split open to show a massive tangle of heartworms. The long, slender worms fill every iota of space in the heart. How could a dog survive with such an infestation? Obviously this dog didn't - a gross and dramatic reminder of the lethal potential of heartworms.

Dogs get heartworms by being bitten by mosquitoes infected with heartworm larvae. Larvae are a tiny, immature stage of the heartworm's development. The only way that the parasite larvae can be transmitted to your dog is via mosquito bite. Dogs do not get heartworms from other dogs.

According to the American Heartworm Society (, heartworm disease has been found in all 50 states. This parasite is a concern for all dogs. It only takes one mosquito bite to infect a dog with heartworm. Once a dog is bitten by a mosquito carrying the heartworm larvae, it takes approximately 7 - 12 months for the larvae to reach adulthood. The adult heartworm lives in the dog's heart and lungs. Heartworms reach lengths between 5-16 inches and can live up to 7 years. Hundreds of heartworms can live in your dog, eventually clogging heart, lung and pulmonary vessels, causing death if untreated.

Symptoms of heartworm infestation in dogs usually begin with coughing and lack of energy as the heart and lungs become congested with adult heartworms. Treatment consists of a series of injections that kill the heartworms. During the weeks of treatment, the dog must be kept quiet and still to try to prevent blockage of pulmonary vessels as the dead worms break up and pass through the body. Exercise too soon after treatment can contribute to blockages and cause death. The treatment is effective; keeping the dog still is the most difficult part. Cost of treatment varies from several hundred to a thousand dollars or more depending on the severity of the infestation.

By far, the best way to deal with heartworm is prevention. A once a month chewable tablet prescribed by your veterinarian is all that it takes to keep your dog safe. Before starting the monthly preventive, your veterinarian will give your dog a simple blood test to make sure your dog is negative for heartworms. Dogs become re-infected every time a mosquito carrying heartworm larvae bites them. Depending on where you live, your veterinarian may recommend that the preventive be given year round for maximum protection.

Tapeworms: Beware the wriggling white rice that you see on your dog's bed, on your carpet or in the anal area under your dog's tail. These little wigglers are tapeworm segments. A tapeworm is a long, flat, white worm made up of multiple segments. Tapeworms feed from the wall of your dog's intestines. The worms are passed from your dog's body via feces. Individual segments can break off and those are "wriggling rice" that you see.

Dogs get tapeworms by eating the tapeworm larvae. Tapeworms require an intermediate host to transmit their larvae to your dog. There are three types of tapeworms that infect dogs, each with a different intermediate host. Rabbits carry one type of tapeworm larvae, fleas another and rats and mice carry a third. In each case, tapeworm eggs are ingested by the host animal (the rabbit, flea, mouse or rat). The tapeworm eggs hatch inside the host, and at this stage the tapeworm larvae are infectious to dogs if the dog eats the host.

Tapeworms live in your dog's digestive track and absorb nutrients through their skin. In a healthy dog, tapeworms may not cause much damage. Tapeworms can heavily infest a dog in poor condition, and cause considerable health problems. Beyond the visible tapeworm segments, behavioral signs of tapeworm infestation include butt scooting across your floor or carpet and incessant licking of the anal area.

Heavy worm infestations may cause inflammation of the gastrointestinal tract including bowel problems, gas, and gurgling stomach noises. General signs of malnutrition may include weight loss and dull coat.

To treat occasional tapeworm infestations, you can get a medication from your veterinarian. For most dogs, fleas are the culprits. To prevent your dog from getting tapeworms, keep your dog from getting fleas through a regular flea control program. Dogs who live in rural areas and are free to hunt rabbits, mice and rats, can continually re-infect themselves with tapeworms even if they have received prior treatment. If your dog is a free-ranger, you may want to discuss with your veterinarian whether periodic prophylactic wormings, such as monthly deworming tablets, are right for your dog.

People rarely get the type of tapeworms that affect dogs. When humans get tapeworms, it is usually from directly ingesting raw or undercooked fish, beef and pork, contaminated water and feces.

With heartworm infestations, an ounce of prevention is worth more than a pound of cure - it's worth your dog's life. One chewable tablet a month prevents this lethal parasite from setting up residence in your dog's heart and lungs. Tapeworms are a gross nuisance and although they do not usually cause serious health problems, they can harm dogs who are not in the best condition. Tapeworms can be kept in check for most dogs if treatment and a regular program of flea prevention are started when tapeworms are detected. With such easy to use solutions available, your dog deserves the chance to be healthy and worm-free. And that butt scooting? It'll be a thing of the past!

Deborah Schildkraut, Ph.D. is a writer and columnist for PETroglyphs and an author of children's books about dogs. She lives with her husband and her two canine companions, Gus and Etta.

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