Biology of the tapeworm:
The adult Dipylidium caninum lives in the small intestine of the dog or cat, attached to the intestinal wall by several suckers. Most people are confused about the size of a tapeworm because they only see its segments which are small; the entire tapeworm is usually 6 inches or more.
The dog or cat becomes infected after swallowing a flea that is carrying a larval tapeworm. The body of the flea is digested away releasing the tiny tapeworm, which looks for a place to latch on to the host's intestine so it can grow a full body. The tapeworm absorbs nutrients through its skin as the food being digested by the host flows past it.
The tapeworm segments are passed from the host’s rectum and out into the world, either on the host’s stool or on the host’s rear end. The segment is the size of a grain of rice and is able to move. Eventually the segment will dry and look more like a sesame seed. The sac breaks and tapeworm eggs are released. These eggs are not infectious to mammals. The tapeworm must reach a specific stage of development before it can infect a mammal and this stage comes much later. At the egg stage, the tapeworm requires a different kind of host to complete its next developmental stage: a flea.
(original graphic by marvistavet.com)
As the larval flea progresses in its development, the tapeworm inside it is also progressing in development. By the time the flea is an adult, the tapeworm is ready to infect a dog or cat. Inside the host’s stomach, the flea’s body is digested away and the young tapeworm is released. It finds a nice spot to attach and the life cycle begins again. It takes 3 weeks from the time the flea is swallowed to the time tapeworm segments appear on the pet’s rear end or stool.
Controlling fleas is essential to prevent recurring infections with this species of tapeworm.
How do you know if your pet has tapeworms?
Because the eggs are passed by the pet in packets (segments), they often do not show up on the fecal exam; the packet must break open for the eggs to be seen under the microscope. This means that it is easy to miss a tapeworm infection if only a microscopic fecal exam is done. In most cases, it is the presence of visible segments on the pet or its stool that confirms diagnosis. Segments can be passed in small groups connected to each other leading the owner to describe a worm that sounds larger than a grain of rice. Tapeworm segments are also quite flat.
Some people will mistake maggots in the stool for tapeworms. Maggots are not seen in freshly passed stool and are not flat.
Can tapeworms infect humans?
Theoretically, yes, people can get them but they must be infected the same way dogs and cats are: by swallowing an infected flea.
How are they treated?
Tapeworms are killed by different medications (praziquantel, which is administered by injection, tablet, or topically, or epsiprantel, which is oral). Fenbendazole is effective against several types of tapeworms but not against Dipylidium caninum.
Why might a pet continue to be infected after treatment?
While many people would like to blame the medication as ineffective, the truth is that there must be an on-going flea population in the pet’s environment. The key to eradicating Dipylidium caninum from the home is flea control.