Nosema disease in honey bees is caused by two species of pathogens, Nosema apis and Nosema ceranae. Nosema apis was the only known microsporidian honey bee pathogen until 1996, when a second species, Nosema ceranae, was identified from the Asian honey bee. Nosema ceranae appears to be the dominant species in the European honey bee (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 honey bee host. – Lee Solter, University of Illinois