One of the common problems we see in dogs and cats is tapeworms. This is also one of the more commonly misdiagnosed problems by clients. I've heard clients think of them as roundworms, pinworms, and many other parasites, as well as simply not knowing what they are. So I thought it was worthwhile to give a quick lesson.
The species of tapeworms we see in pets generally come from one of two sources: fleas and rodents. Fleas the most common source, and it's common to see a pet with a flea infestation also be infected with hookworms. Cats who are "mousers" are commonly infected with a different species of worm. In either case the tapeworm spends part of its life cycle developing in the intermediate host. That host (flea or rodent) has to be swallowed by a second host and then develops into a full-grown tapeworm.
It's actually uncommon to see tapeworm eggs on a microscopic fecal exam routinely performed by veterinarians. Rather than shedding eggs, tapeworms shed segments called proglottids. These segments are easily seen on the feces, in the fur around the rectum or tail, on a pet's bedding, or even crawling directly from the anus. When they are fresh they can be an inch or so long, white, flat, and usually move with a stretching motion. As they age and dry up they shrink and turn an off-white to tan color. We often describe them as looking similar in size and appearance to a grain of rice. Here are some pictures.
Thankfully, tapeworms aren't generally a serious health concern. They sit in the intestinal tract and absorb food that passes through. In severe cases this can lead to weight loss and even malnutrition, but normally just causes loose stools and looks gross. Standard over-the-counter medications for roundworms and hookworms will NOT kill tapeworms, so check with your vet about proper medications.
Gross trivia of the day...Did you know that at one time medications containing tapeworms were sold as weight loss aids? Seriously....