Tapeworms are considered segmented flatworms, belonging to a class of organisms called Cestoda. One important characteristic of this class is that all utilize intermediate hosts in their transmission cycle. Intermediate hosts can include rodents, fleas, and other insects, rabbits, sheep, swine, cattle, and in some instances, even humans!
Tapeworm segments containing eggs are shed in fecal material. When these eggs are accidentally or voluntarily consumed by an intermediate host, they hatch and the resulting larvae migrate into the body tissues and begin their development. Yet they won’t reach their adult stage inside the tissues of this intermediate host. Instead, the life cycle is completed when this host or portions thereof are consumed by another, called the definitive host. Inside this new host environment, the larvae then proceed to develop into adult tapeworms, which attach to the intestinal wall, eat, and repeat the life cycle all over again.
The extent of disease caused by tapeworms depends on the type of worm involved, and if the affected individual is an intermediate or final host. As a rule, adult tapeworms living within the intestines of a definitive host are seldom life-threatening, causing varying degrees of gastroenteritis and malnutrition. Larval forms, on the other hand, tend to do more damage, simply because they migrate through the body tissues. Furthermore, if these larvae gain entrance into the tissues of an animal (or human) that is not a normal intermediate host for that tapeworm, the results can sometimes be deadly.
By far the most prevalent species of tapeworm seen in dogs and cats is Dipylidium caninum, the double-pored tapeworm. It is so common because it uses the flea as an intermediate host (the dog louse can also be a carrier).
Segments from the tapeworm are passed in the feces or actually “crawl” out onto the haircoat of an infested animal. Once outside, the segments dry out and release egg baskets into the environment. Flea larvae looking for food then ingest these eggs, and a new tapeworm begins its development. If the flea happens to be ingested by a pet during chewing or self-grooming episodes, the tapeworm larvae will continue to develop into adult worms within the pet’s small intestine.
Although less frequently, dogs and cats can become infected with other types of tapeworms besides Dipylidium, depending on potential exposure to intermediate hosts. For instance, dogs fed raw meat or garbage are at risk. Echinococcus granulosus, the tapeworm responsible for hydatid cyst disease, is often transmitted to dogs in this way. The hunting habits of outdoor domestic cats put them at high risk of exposure to this parasite as well.
Dogs and cats infested with adult tapeworms may or may not exhibit the typical signs associated with gastroenteritis, such as vomiting and diarrhea. Weight loss certainly can occur as the worms absorb nutrients from within the gut. Often, scooting and other signs related to anal sac discomfort might also tip off an owner as to the presence of these pesky parasites.
Diagnosis of a tapeworm infestation can be confirmed by actually seeing the white, moving, wormlike segments in fresh fecal material or on the haircoat around the hind region. Segments might also be seen on anal sac expression. If dried, the segments will take on a brownish, “ricelike” appearance.
Microscopic examination of the stool might be helpful as well; however, because the shedding of the segments is sporadic, a negative finding cannot totally rule out an infestation.
Tapeworms can be difficult pests to treat and totally eliminate. Praziquantel and epsiprantel are two effective medications used by veterinarians to eliminate tapeworms from the intestines. Other drugs are available as well. Repeating the treatment in 2 to 3 weeks helps ensure thorough elimination.
Flea control is the best way to prevent Dipylidium caninum. Other tapeworms, including Echinococcus, can be prevented by denying access to garbage and/or raw meat, and discouraging the hunting habits of felines.