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176 CHAPTER 7

Source: Centers for Disease Control and Prevention (CDC)

FIGURE 7-14 D. caninum life cycle

in the host’s feces and ingested by fleas that may be Morphology
accidentally ingested by another mammal after the tape-
worm larvae have partially developed (Figure 7-14). The adult tapeworm may range from 10 to 50 cm in
The species of fleas found on dogs and cats, Cteno- length. The scolex has a rostellum with four rows of
cephalides canis and C. felis, respectively, may both be small hooklet-like spines on a cone-shaped rostellum,
implicated in transmitting D. caninum to humans and along with the 4 suckers typical of all cyclophyllid ces-
other animals. todes. The uterus in a gravid proglottid will contain a
As in all members of family Dipylididae, pro- large number of packets of eggs with as many as 5 to
glottids of the adult have genital pores on both sides 20 eggs in each packet. The eggs of D. caninum are
(hence the name double-pore tapeworm). Each side has somewhat colorless and are roughly 30 to 60 μm in di-
a set of male and female reproductive organs. In cats, ameter with a 6-hooked arrangement of the oncosphere
sometimes proglottids are visible hanging out of a cat’s present in each egg. Eggs are enclosed in membranous
anus. When inside fleas, the eggs hatch and form on- packets.
cosphere larvae that move through the wall of the flea’s
intestine into the body cavity where they develop into Symptoms
cysticercoid larvae and become infective to mammal
hosts. As with most tapeworm infections, control of flea Although some individuals with a heavy worm infec-
populations on pets is the best way to prevent human tion will experience mild symptoms of gastrointestinal
infection. distress, such as nausea and vomiting, diarrhea, and