PREVALENCE AND GEOGRAPHIC DISTRIBUTION
The reported prevalence of tapeworms in the Americas in published studies varies from 4% to 60% in dogs and 1.8% to 52.7%
in cats.3-5 A number of factors influence the likelihood that a particular dog or cat will become infected with tapeworms, including
the geographic region where the animal lives and the opportunity it has to ingest an infected intermediate host. Prevalence
data generated by fecal flotation alone almost certainly underestimate the frequency of infection with Dipylidium caninum and Taenia species. Because proglottids, and thus eggs, are focally distributed in fecal material, a given fecal sample may not contain
tapeworm proglottids or eggs even in the presence of an infection.3
Dipylidium caninum and Taenia species are found throughout North America. Mesocestoides species is less common than either D. caninum or Taenia species but does occasionally appear in foci throughout the United States. At present, Echinococcus species are thought to be largely limited to areas of Alaska and of the north-central, midwestern, and southwestern United
States as well as areas of Canada.6
Spirometra and Diphyllobothrium species infections in dogs and cats are not as common as infection with cyclophyllidean cestodes, and studies reporting prevalence
estimates have not been published. However, these tapeworms are known to be common in pets in some areas of the United States.
Diagnosing infection with Dipylidium caninum or Taenia species is achieved by identifying proglottids in the fecal material (Figure 1) or by recognizing the eggs on fecal flotation (Figures 2 & 3). When freshly shed, D. caninum proglottids have rounded edges and are often described as cucumber seed in shape, whereas those of Taenia species are more rectangular with sharp corners. Often, D. caninum or Taenia species infection is diagnosed based on a client's observation of proglottids, which can be motile when fresh or appear like
grains of rice (or sesame seeds) when desiccated on or around the pet. When desiccated, the proglottids lose their characteristic
shape. In these cases, the dried tapeworm segments can be rehydrated in saline solution, the tissue teased apart, and the
material examined microscopically for the presence of characteristic eggs. Sterile cestode segments are often produced; however,
the absence of eggs in a proglottid does not rule out the presence of a tapeworm infection. In addition, because proglottids
are not uniformly distributed in the fecal material, fecal flotation alone is not a reliable means of diagnosing tapeworm
infection in dogs and cats.
Figure 1. Dipylidium caninum proglottid and segments on a fecal mass.
Echinococcus species proglottids will not be grossly detected, and infection can only be identified by fecal flotation. Similarly, Spirometra and Diphyllobothrium species eggs can only be found on fecal examination (Figure 4), although occasionally, long segments of adult Spirometra or Diphyllobothrium species may be found in vomit or feces. In these cases, the adult tapeworms can be identified grossly by the presence of
a distinct medial genital pore.7
Figure 2. A packet of Dipylidium caninum eggs. Individual eggs of D. caninum have refractile hooks inside the egg, and each measure about 40 to 50 μm in diameter but are usually shed in packets containing
25 to 40 eggs. The size of the entire packet varies somewhat but may be 120 to 200 μm long.