A Few Thoughts on Tapeworms

Linda Aronson, DVM

The most common tapeworm species in the United States is Dipylidium caninum.  Animals – including dogs, cats and humans – get the tapeworm by consuming – often inadvertently – infected adult fleas.  The flea contains an infectious cysticercoid which emerges in the small intestine, and attaches itself to the wall.  It is here the adult tapeworm forms.  Within 2 or three weeks the tapeworm sheds egg filled proglottids which are passed in the dog’s feces.  These are ingested by flea larvae – which eat dog feces as well as flea feces!  The tapeworm egg matures with the flea.

Proglottids and eggs are not evenly spread through the feces, and the odds of finding them on a single fecal exam are small.  If you have abundant fleas it is probable that your dog has Dipylidium infection.  The monthly heartworm treatments do not treat tapeworms.  Praziquantel – found in Droncit or Drontal – does effectively kill tapeworms.  Reinfection is common and a second dose should be given two weeks after the initial one.  Some veterinarians recommend adding praziquantal to the monthly preventative regimen.  However, nasty though they may sound, tapeworms produce little effect on the animal.  There have been reports of impaction sometimes fatal in puppies. 

The other species of tapeworm that can infect out dogs is Taenia.  Proglottids are shed as with Dipylidium, but the eggs are ingested by other mammals.  There they hatch and migrate into other organs, usually the liver.  There the larvae form large fluid filled cysts.  Consumption of the infected liver introduces the larvae into the dog, and they also attach to the small intestinal wall and mature and produce proglottids.  Consuming infected mice (Taenia taeniaeformis) or rabbits (Taenia pisiformis) is the normal cause of infection, although other species of Taenia have been reported, as have Echinococcus spp.  Treatment is the same as for Dipylidium.     

While they rarely cause significant problems in dogs, their zoonotic ability to infect humans is often of concern.