Tapeworms are intestinal parasites that are transmitted through fleas, rabbits or other mammals. A number of different tapeworm species can infect dogs, but the most common variety is a species called Dipylidium caninum. Diplidium tapeworm infections rarely cause serious physical harm to dogs, and the risk to humans is small.
According to the Mar Vista Animal Medical Center, Dipylidium caninum tapeworms often grow to be six inches or longer. They have a device called a rostellum, which Mar Vista describes as looking like a hat with hooks on it, that they use to attach themselves to the intestinal wall so that they can drain nutrients from their canine host. Six rows of teeth help the worms to maintain their grip.
Dipylidium tapeworm bodies are divided into numerous segments. Many people believe that tapeworms are actually very small because they only see individual segments of the worm, but in actuality, the sections that pet owners see are called proglottids. Proglottids are small sacks of tapeworm eggs that are passed out of the body through the dog's anus as part of the reproductive cycle. They look like small, flat grains of rice.
According to the Pet Education website, dogs with tapeworm scoot around on the floor or lick their anal area. Extremely infested dogs may also have chronic anal itching and stomach pain. However, the most noticeable symptom of a tapeworm infection are proglottids or tapeworm egg sacs in the stool. The sacs may appear to wriggle or move. Tapeworm eggs may be visible in the feces if the egg sac ruptures.
Dogs infested by tapeworms often have dried proglottid sacs attached to the hair around the anus. These packets are usually around 1/16" in length. They are yellowish in color and are hard to the touch.
Dogs sometimes also vomit tapeworms. A tapeworm that loses its grip on the dog's intestine may be released into the stomach. The worm nauseates the dog, and the dog vomits the worm out of its body. The eliminated worm is usually several inches long.
Dogs become infested with Dipylidium caninum tapeworms by ingesting fleas. Larval fleas and tapeworm eggs both live in the soil. Larval fleas eat tapeworm eggs along with flea dirt. The baby tapeworm matures inside the flea. Adult fleas, which obtain their nutrients from blood, jump on dogs and cats. They cause itching when they bite the animal, and the dog often bites back, chewing at the irritated site. Sometimes the dog accidentally swallows the flea and the larval tapeworm with it. The tapeworm matures to adulthood inside the dog's small intestine.
Another tapeworm species called Echinococcus also infects dogs; the Pawprints and Purrs website explains that Echinococcus tapeworms are transmitted to dogs when they eat rodents that carry the parasites inside them. Echinococcus infections can cause serious illness in infected humans.
Different kinds of de-worming medication in the form of tablets or injections are used to kill tapeworms. Mar Vista explains that the tapeworm does not pass out of the body intact; instead, it is digested by the body and eliminated. The pet owner may need to have his or her dog treated for fleas to make sure that it does not become reinfected at a later date.