Cysticercosis (Fox Tapeworm) in Dogs: Symptoms, Causes and Diagnosis

Dog's face
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You love your dog and want to keep him safe. But sometimes, the environment seems at odds, with every nook and cranny a potential minefield of infection and disease. From ticks to fleas, whipworms to roundworms, and those nasty nematodes, parasites and pathogens lurk around every corner, behind every tree, in the soil, in the water, and in the feces of wild animals — for example, fox tapeworms, which cause cysticercosis in dogs.

All tapeworm infections in dogs are not created equal; most are easy to get rid of, causing only mild symptoms. But cysticercosis, known as fox tapeworm infection, can have severe outcomes, particularly for elderly dogs or immune-compromised young dogs. Although it's a rare disease, according to the Canadian Animal Health Institute, it is considered an emerging threat in some regions of the U.S. and Canada — and it can be deadly. Fortunately, many dogs have no symptoms whatsoever.

One of more than 60 taeniid species of tapeworms that exist worldwide, Echinococcus multilocularis, a member of the tapeworm family Taeniidae, is unique among them for its capacity to rapidly reproduce inside a dog's body. The organism originates in the feces of wild canids such as infected foxes or coyotes and is known as a proliferative cysticercus because it multiplies in an asexual process called budding. Consequently, it takes only one or two of the parasite's to morph into a massive infection in the tissues of the liver, abdomen, lungs, muscles, and the tissues under the skin where it forms cysts. While most other tapeworm segments look like cucumber seeds or grains of rice and are visible in your dog's fur, fox tapeworms are tiny, about 3- 6mm long, and not readily discovered.

Mature Proglottid, Dog Tapeworm (Taenia pisiformis), 10X at 35mm. Shows: testes, ovary, uterus, yolk gland, shell gland, vagina, sperm duct and genital pore. Flatworm (Phylum Platyhelmintes), hermaphrodite.
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Cysticercosis associated with E. multilocularis occurs in people as well — its source unknown. Thankfully, it is not a zoonotic disease at any stage, so you don't have to worry about contracting cysticercosis from your dog.

How does a dog become infected with cysticercosis and what are tapeworms?

Fox tapeworm infection occurs when a dog ingests E. multilocularis' eggs or sometimes the larvae (cysticerci) found in the feces of infected foxes or coyotes that contaminate vegetation and the surrounding environment. Most dogs delight in rolling around in anything pungent, including other animals' droppings, and can easily pick up the parasite this way. Similarly, sniffing the ground or playing with sticks and other objects outdoors, or directly eating fox or coyote feces can be the mode of infection. In the case of coprophagic dogs, autoinfection occurs when the dog reinfects himself by eating his own stool containing the parasite's eggs.

Tapeworms in dogs (and cats) are parasites, which means their lives depend on the exploitation of one or more hosts. Their life cycles are known as complex or indirect because tapeworms need two mammalian hosts for their various life stages versus a parasite with a direct life cycle that needs only one host, for example, fleas or whipworms.

A dog is a definitive host for tapeworms or the one in which the tapeworm matures, reproduces and generates eggs. The intermediate host eats the parasites' eggs from an environment contaminated by the definitive host. In turn, the eggs hatch into the immature or larval stage (metacestode) and develop inside the intermediate host, such as a rodent. If a dog eats an infected rodent, he will ingest the adult form of the tapeworm and spread the disease throughout his environment.

Gravid Proglottid, Dog Tapeworm (Taenia pisiformis), 4X at 35mm. Shows a highly branched uterus with fertilized eggs (zygotes). Remnants of sperm duct, vagina and genital pore still visible. Flatworm, hermaphrodite.
credit: Ed Reschke/Photolibrary/GettyImages

Symptoms and clinical signs of cysticercosis.

At first, your dog may not have any clinical signs of fox tapeworm infection. It's not until clusters of the parasites invade his tissues that symptoms are observable. See your veterinarian at once if you spot any of these abnormal behaviors and symptoms of cysticercosis in your dog:

  • Lethargy or sluggishness.
  • Weakness caused by anemia.
  • Yellowing of the skin which occurs if the parasite is in the abdominal cavity.
  • Loss of weight or anorexia.
  • Respiratory difficulty.

How does a veterinarian diagnose fox tapeworm infection or cysticercosis?

If you suspect cysticercosis, collect a stool sample from your dog to take with you to the veterinarian. The vet will perform a complete physical examination and review your dog's medical history. You will be asked for your observations of symptoms and your dog's recent activity, so it's wise to keep notes to aid in diagnosis.

Blood work with a complete blood count and urinalysis are routine diagnostic tools. A biochemistry profile will reveal any abnormality in the functionality of the internal organs and electrolyte count. X-rays and other imaging diagnostics are used to detect the cysts and determine if the masses are instead cancerous tumors. The stool sample will be evaluated for the presence of the parasite's eggs, but in itself, is not proof positive since it's hard to distinguish different parasites by their eggs only.

Little playful Jack Russell Terrier dog playing in garden in morning
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Treatment protocol for cysticercosis.

The treatment for cysticercosis consists of either antiparasitic medications and dewormers or surgical removal of the tapeworms. Both are effective means of ridding your dog of the worms.

In surgical removal, your veterinarian removes the front or interior end of the tapeworms which are attached to your dog's tissues by hooks and suckers. Anthelmintics are antiparasitic medications that kill the parasites which are then expelled.

How to prevent your dog from getting infected by fox tapeworm or cysticercosis.

Prevention of fox tapeworm infection in your dog is as simple as avoiding wildlife habitats, keeping a watchful eye on your dog and what he's eating when he's outside and curbing the sniffing of and rolling around in "smelly stuff" habit. If you're in an area with reports of cysticercosis in dogs, keep your canine pal on-leash when navigating the trails, forest areas and bush.