It can take months or years to notice any signs of a tapeworm. They can include: mild nausea; diarrhea; abdominal pain; loss of appetite; weight loss; Sometimes, a person can feel a piece of the worm coming out through the anus or see it in their feces. There are different types of tapeworm. One (fish tapeworm) can cause anemia because it absorbs vitamin B12, which helps make red blood cells.