Cause of Tapeworms in Dogs
There are several different species of Tapeworm that may cause a Tapeworm infection in a dog.
Dipylidium Canium
This tapeworm is also known as the Common Dog Tapeworm, the Cucumber Seed Tapeworm, the Double-Pored Tapeworm, and the Flea Tapeworm. The host for this Tapeworm is generally either fleas or lice, which host a D. Canium larvae. This larvae is produced when either of these organisims ingests a D. Canium egg, which then hatches. When a dog ingests the infected organism, the larvae develops into its mature form, and subsequently infects the dog.
Taenia (several species)
There are nine different species of the Taenia Tapeworm, though only six of these species have dogs for their definitive host. The intermediate host (the organism that harbors the immature form of the Tapeworm) usually ingests tapeworm eggs from the fecal matter of another organism. The intermediate host then harbors the larvae, which produces a fluid-filled sac that gives the immature Taenia larvae supplemental nourishment. These sacs may be ingested by dogs (the definitive host), which then causes the immature Taenia larvae to mature into its adult form.
Echinococcus Granulosus, Echinococcus Multiocularis
Intermediate hosts for the Echinococcus Tapeworm include sheep and other herbivores. These species of Tapeworm reach their immature form, and then migrate to the lungs or liver of the intermediate host. Infectious cysts develop in the host, usually containing thousands of infective forms. Each of these forms, when ingested by a dog, will cause a Echinococcus Tapeworm to develop in its mature form. In dogs, this tapeworm usually resides in the small intestine.
Diphyllobothrium Laturn
This species of Tapeworm is also known as the Broad Fish Tapeworm. Diphyllobothrium Laturn has two different intermediate hosts, and four different life stages. In the first life stage, the eggs of the D. Laturn are ingested by the first intermediate host, which are Copepods (freshwater crustaceans). The D. Laturn mature into their second stage, and the Copepods may be ingested by minnows or other fish. If this occurs, the D. Laturn mature into their third stage inside the fish's tissues. Dogs may become infected by consuming infected fish, which causes the worm to mature into its fourth (adult) stage.
Spirometra Mansonoides
The life cycle of the Spirometra Mansonoides is similar to that of the Diphyllobothrium Laturn Tapeworm. The first intermediate host is a Copepod, which is then ingested by the second intermediate host. With S. Mansonoides, this host may be a snake, bird, rodent, reptile or other amphibian. A dog may become infected by consuming one of these second intermediate hosts.