Enterocytozoon bieneusi, a fungus of the microsporida phylum is an obligate intracellular parasite that infects intestinal epithelial cells. The linear DNA genome is estimated at 40 Mb, organized in 3 or 4 chromosomes with a total of 3,804 genes, 1,702 of these encoding functional proteins. This species infects human and other mammals causing microsporidiosis and many associated opportunistic infections which have had a serious economic impact on the swine industry particularly. Infective E. bieneusi spores are hardy and can survive in the environment for long periods of time. The oval shape is created by two extracellular walls surrounding a membrane containing the sporoplasm, the infectious material. Upon ingestion with contaminated food stuffs or water, the extrusion apparatus comprising an anchoring disk, polar tubule, and polaroplast extend from the spore piercing the host cell membrane. The sporoplasm is then injected through this apparatus into the host cell, primarily the intestinal epithelium. Within the host cell, proliferation by sporogony occurs in the cytoplasm and is followed by maturation. The resultant new spores cause host cell death by disrupting the host cell membrane leading to release into the intestine allowing for subsequent infection of surrounding cells or excretion and transmission. E. bieneusi causes microsporidiosis in humans, specifically in immune-compromised individuals and has been linked with the wasting and chronic diarrhoea seen in individuals with AIDS. Other symptoms include urinary tract infections and bowel perforation, cough and laboured breathing due to infection of the lungs, and inflammation of the brain and muscle tissue in cases with the fungi has spread to other parts of the body. Fumagillin and Albendazole have been effective in treatment to a certain extent along with treatments utilising inhibitors of chitin synthase enzymes.