Major Concerns: Studies are limited, but one 12-year study identified 124 deaths in the United States, but 1000s internationally.

Tapeworms generally enter the intestines of animals (including humans) through contaminated food, fleas, or rodents and feed off ingested nutrients. Over the first two months they grow steadily to about 25 feet, sometimes quite a bit more. Eventually they attach themselves to the intestinal walls, and feed off the nutrients that pass by. Here they can cause abdominal pain, diarrhea, and nausea, but generally it is treatable. If they settle outside the intestinal area, they do serious damage, attacking the tissue and muscles, possibly causing seizures.