Encephalitozoon intestinalis is a parasite. It can cause microsporidiosis. It is notable as having one of the smallest genome among known eukaryotic organisms, containing only 2.25 million base pairs. Its genome was completely sequenced in 2010. E. intestinalis originally named Septata intestinalis, was reclassified based on morphologic, antigenicand molecular similarities with other species of the genus Encephalitozoon. Recently, Some domestic and wild animals have been found to be naturally infected with E. intestinalis and some other microsporidian species.