After entering the body in contaminated food, Shigella group bacteria infect cells that line the inside of the intestines and often produce a toxin. The toxin affects both the intestines and the nervous system. Cells of the intestinal lining are damaged, which causes inflammation and bleeding. The infected person experiences diarrhea (possibly bloody), abdominal cramps, and small stools. Effects of the toxin on the nervous system commonly include fever and rarely other symptoms, such as seizure. Nervous system symptoms are most severe in young children.