Enterocytozoon bieneusi is a species of the order Chytridiopsida (in the division Microsporidia) which infects the intestinal epithelial cells. It is an obligate intracellular parasite. Microbiology Enterocytozoon bieneusi, commonly known as microsporidia, is a unicellular, obligate intracellular eukaryote. Their life cycle includes a proliferative merogonic stage, followed by a sporogonic stage resulting in small, environmentally resistant, infective spores, which is their transmission mode. The spores contain a long, coiled polar tube, which distinguishes them from all other organisms and has a crucial role in host cell invasion. E. bieneusi was first found in an AIDS patient in France in 1985 and was later found in swine in 1996 in fecal samples. It causes diarrhea—thus the pigs excrete more spores, causing the disease to spread. As this pathogen is very prevalent throughout the world, E. bieneusi is found in a wide variety of hosts including pigs, humans, and other mammals. E. bieneusi can be studied using TEM, light microscopy, PCR and immunofluorescence and can be cultured for short-term. It is not yet known whether the pathogen itself can be infected by other diseases. There seems to be widespread economic implications of infection by this pathogen for the swine industry. Several treatments, including fumagillin and albendazole have showed promise in treating infection (Mathis et al. 2005). Discovering the disease The earliest reference to the order Microsporidia was in the mid-20th century. E. bieneusi was first found in an AIDS patient in France in 1985. The electron microscope studies revealed presence of developmental stages of parasite resembling microsporidia. The investigators then named it as E. bieneusi (Desportes et al. 1985). The presence of E. bieneusi in swine was first detected in fecal samples of pigs in Zurich, Switzerland in 1996 (Deplazes et al. 1996) Culturing Short-term culturing of E. bieneusi was achieved by inoculating duodenal aspirate and biopsy specimens into E6 and HLF monolayers. The short-term cultures lasted up to 6 months. After several weeks of culture, gram-positive spore-like structures measuring 1 to 1.2 um long were observed. Mature spores and sporoblasts with double rows of polar tubule coils were seen (Visvesvara 2002). Long term culturing seems to be unsuccessful. Study and detection methods Light microscopy of stained clinical smears, especially of fecal samples, is used to diagnose microsporidia infections.. Transmission electron microscopy is required to differentiate between species of microsporidia, but it is time consuming and expensive. Immunofluorescence Assays using monoclonal and