Nosema disease in honeybees is caused by two species of pathogens, Nosema Apis and Nosema Ceranae. Nosema Apis was the only known microsporidian honeybee pathogen until 1996, when a second species, Nosema ceranae, was identified from the Asian honeybee. Nosema ceranae appears to be the dominant species in the European honeybee (Apis mellifera) in many parts of the world, including in Europe and the United States. Both of these pathogens cause chronic deleterious effects in the honeybee host. – Lee Solter, University of Illinois