Dogs frequently get tapeworms by ingesting adult fleas, which serve as hosts for tapeworm larvae. This usually occurs during self-grooming. Birds, rabbits and rodents may also carry the larvae, and a dog may eat these animals during hunting or scavenging.
Dipylidium caninum is the tapeworm that most commonly infects dogs. Tapeworms are made up of segments called proglottids, each about the size of a grain of rice. They attach to the intestinal wall with hooks and suckers, absorbing nutrients as food passes through the intestine. As the tapeworm matures, these tapeworm segments break off and pass into the stool.
Tapeworms don't usually cause serious problems unless the dog is heavily infected. Weight loss may occur in those situations. However, the proglottids irritate the skin around the anal area, and dogs may "scoot" themselves along the floor in order to alleviate the itching and irritation. Tapeworms are transmissible to humans, with most cases found in children.
The drug praziquantel is used to treat infected dogs. It is given either orally or as an injection, and is usually well-tolerated. The drug dissolves the tapeworm within the intestine. Flea control is also important in the treatment of tapeworms, since they are the intermediate larval hosts. The entire environment, inside and out, needs to be treated to minimize reinfection.