Tapeworms are internal parasites that live inside of the small intestines of their mammalian hosts. They can range from less than an inch to several feet in length. Surprisingly, tapeworms usually don't cause serious harm to their canine hosts, other than occasional abdominal discomfort, anal itchiness, weight loss and general ill thrift. The main tapeworms that infect domestic dogs are Taenia pisiformis, Dipylidium caninum, Echinococcus spp., Diphyllobothrium spp. and Mesocestoides. The medical name for infection with tapeworms is "cestodiasis."
Causes of Tapeworm Infection
Dogs become infected with tapeworms by eating an intermediate host that contains tapeworm eggs, larvae or cysts. Intermediate hosts are organisms that other organisms, usually parasites, live inside of while they are going through some transitional stage of development. For example, the parasite may hatch from an egg into its larval form inside of its intermediate host. The intermediate host may or may not also act as the carrier, or vector, that transmits the parasite to its ultimate victim.
Dogs pick up Taenia, Echinococcus and Mesocestoides tapeworms by eating raw or undercooked flesh of a bird, reptile, sheep, cow, goat, deer, elk, horse, pig, rabbit, rat or other intermediate host that is carrying some form of the parasite. Diphyllobothrium tapeworms are found encysted in the organs of fish, primarily in the northern United States and parts of Canada. Dogs become infected with those parasites by eating fish that are infected with the cyst form of the worm. Dogs get the fairly common Dipylidium caninum tapeworms when they eat infected adult fleas or lice. Fleas and lice become infected when they ingest the eggs of the parasite when feeding on the blood of an infected mammal.
Regardless of how they initially get inside of a dog, tapeworms eventually end up in the dog's small intestine. The parasites bury their heads into the lining the dog's small intestine and attach themselves to that sensitive tissue. There, they feed on the dog's blood, depleting the animal of essential nutrients and, in cases of serious parasite loads, draining it of essential blood, as well. Tapeworms grow, mature and eventually reproduce inside the dog's small intestine. Adult tapeworms typically remain there indefinitely. Adults produce and carry eggs in separate segments of their increasingly long bodies; these segments are also referred to as "egg packets." Those body segments eventually break off and are passed out in the infected dog's feces. Many times, tapeworm egg packets are motile, meaning that they can move independently (on their own) in the outside environment.
Prevention of Tapeworm Infection
The best way to prevent or eliminate tapeworm infection in companion dogs is to follow a regular de-worming program using products recommended by the dog's veterinarian. Flea control is also extremely important. People can become infected with tapeworms if they come into contact with and accidentally ingest a bit of feces from an infected dog, or if they swallow an infected flea or louse. Good hygiene is essential to prevent both canine and human infection by tapeworms. People should avoid eating raw or undercooked meat that comes from animals that are known to be potential intermediate hosts of the larval stage of these parasites, such as sheep, cattle and rabbits. Dogs should not be permitted to eat dead animals or other raw or undercooked wild game.
Because of their indiscriminate oral experimentation, young children have an increased risk of "getting tapeworms", either by inadvertently consuming adult fleas or lice or by swallowing a bit of feces from an infected animal. This can happen, for example, when a dog licks a child's face, or when a child playing outside touches infected fecal material and then puts its fingers into its mouth. Because humans are not their definitive hosts, adult tapeworms usually don't mature inside of people. Instead, in people, tapeworm larvae tend to form large cysts, called "hydatids," mostly in the liver, lungs and brain. Hydatid cysts in humans can cause extremely serious disease. They can even be fatal.
How Tapeworms Affect Dogs
In most cases, dogs with tapeworms do not show many signs of discomfort or distress. Frequently, they act (and presumably feel) completely normal, even if they have a severe tapeworm infection. It is very common for owners to be astonished, and usually disgusted, when they find out that their dogs are carrying a heavy tapeworm load. While these parasites survive by sucking blood and key nutrients out of their canine hosts, they tend to do so slowly and steadily over a long period of time, without causing any sudden symptoms or dramatic changes in the dog. Certainly, dogs with tapeworms probably will lose weight over time, but it will happen so gradually that it will be almost imperceptible to their owners. It is unusual for dogs with tapeworms to show overt signs of intense abdominal pain or discomfort, even though it seems that those symptoms would show up in dogs infected with blood-sucking intestinal parasites.
Symptoms of Tapeworms
When symptoms of tapeworm infection do occur, they usually are nonspecific. Owners of dogs infected with tapeworms may notice one or more of the following:
Anal and perianal itchiness (pruritus at and around the anus)
Licking at the anal and perianal area
Weight loss (despite maintaining a good appetite)
Increased appetite (without weight gain)
Poor hair coat (dull, dry, unkempt)
Poor skin condition (dry, flaky)
Abdominal pain (less common)
Owners may notice tapeworm segments stuck to or crawling through the fur around their dog's anus. These resemble grains of white rice or white sesame seeds. Affected dogs often scoot their bottom along the ground in an effort to relieve the itchiness and irritation caused by tapeworms. Uncommonly, heavy loads of adult tapeworms cause partial or total intestinal obstruction, which can be a true medical emergency.
Dogs at Increased Risk
Free-roaming dogs with access to freshly killed wild or domestic animals are at increased risk of developing tapeworm infection. Dogs with heavy lice and/or flea loads have a greatly increased risk of tapeworms, as well.
Diagnosis and Test
Tapeworm infection in dogs is not particularly difficult to diagnose. The most common way to detect tapeworms is by fecal flotation. This procedure involves processing a fresh stool sample and examining the end-product under a microscope for tapeworm eggs, which are quite large and usually are readily distinguishable from the eggs of other intestinal parasites. Sometimes, a dog will have tapeworms, but the particular stool sample will not contain any eggs, or at least not enough eggs for the veterinarian to identify. This is called a "false negative" test result. In other words, the dog is infected with the parasite, but the test turns out negative. It is important to repeat fecal flotations several times, on different stool samples, to be sure that an initial negative result was not a false negative.
Another way to diagnose tapeworms is to apply a piece of cellophane tape to the dog's anal area, gently remove the tape and then apply it sticky-side down directly onto a glass slide. The veterinarian will look at the sample microscopically to see what, if any, eggs or organisms are present. This procedure can be used to identify egg packets and eggs of certain types of tapeworms. Many times, dogs with tapeworms will actually have worm segments stuck to or crawling on the fur around their anus (this is called the "perianal area"), and in their feces. These actually are pieces that have broken off from adult worms, and they can be seen by the naked eye. Most owners understandably find it aesthetically offensive to see parts of these parasites crawling around on their dog's anus, fur or feces. Fortunately, once they are diagnosed, tapeworms in dogs are not hard to treat.
If an owner notices that her dog has particles resembling white rice in its perianal area or in its "poop," she should collect a fresh stool sample and consult with a veterinarian about appropriate treatment for tapeworms.
A dog should be treated for tapeworm infection when eggs or egg packets are detected in its fecal sample or when worm segments are detected around its perianal area. Treatment should also take place in the less common case where tapeworms are diagnosed in a dog that presents to a veterinarian with symptoms of weight loss, abdominal pain and general ill-thrift. The goals of treating tapeworms are to remove adult worms from the gastrointestinal tract, eliminate shedding of infective eggs and larvae, and prevent cycles of re-infection.
The only way to complete cure a dog of tapeworms is to destroy the heads of all of the parasites – especially those that are attached to the lining of the small intestine. If the heads are not destroyed, the tapeworms can regenerate, much like a lizard can regrow its tail. There are a number of de-worming medications that successfully treat tapeworm infection. However, they are not necessarily the same drugs that are effective against other types of internal parasites. Many owners make the mistake of buying over-the-counter de-wormers on the assumption that they will get rid of all intestinal parasites, including tapeworms. Only a veterinarian can identify the precise medication, and the dosage, that is appropriate for a dog with a particular species of tapeworms.
Even the most effective tapeworm medicines will not prevent re-infection if there are adult fleas or lice in a dog's environment, or if the dog has access to rabbits, rats, rodents or other infected intermediate host animals. Both the dog and its environment must be treated and managed to ensure that the tapeworm lifecycle is effectively broken.
The prognosis for dogs with tapeworms is excellent, as long as their owners follow appropriate treatment and de-worming protocols.