Porcine epidemic diarrhea (PED) was first described in England in 1971 in growing pigs and the causative agent, porcine epidemic diarrhea virus (PEDV), was identified in 1978. The virus spread to the rest of Europe where it caused outbreaks of diarrhea and significant losses throughout the 1970s and 1980s. PEDV is considered endemic to Europe today, but does not cause widespread significant disease. In parts of Asia outbreaks were recognized first in 1982 and have continued to occur since. In May of 2013 PEDV was identified in swine for the first time in the United States. The virus has caused severe diarrhea in sows and piglets, with near 100% mortality in piglets across a wide geographical area of the United States. Genetic analysis of PEDV isolates from affected farms in the US found the virus to be 99% genetically similar to isolates from China, but efforts to determine the source of entry to the United States have been unsuccessful.