Pigs of all ages are susceptible to intestinal diseases, and diarrhea is the sign common to nearly all such disorders. Transmission of infectious agents that cause enteropathies is by the fecal-oral route. At least 16 different etiologic agents, including bacteria, viruses, and parasites, can cause primary intestinal disease. Porcine circovirus type 2 (PCV 2) virus may be isolated from the intestines of pigs with diarrhea. PCV 2 is the cause of several multisystemic diseases in pigs, including postweaning multisystemic wasting syndrome (see Porcine Circovirus Diseases). Diarrhea in a herd may be due to a single agent, but concurrent infections are common. Because some diseases are age-dependent, differential diagnosis is best considered by age group (see Table: Distribution of Diarrheal Diseases in Pigs by Age Group).