A higher virulence of N. ceranae, if conclusively demonstrated to be the case, could account for the unusual reported course of nosema disease in central and southern Europe over the last few years, in which nosema disease is a year-round phenomenon rather than a spring disease, and is associated with higher colony losses (Hatjina and Haristos, 2005; Higes et al., 2005; Imdorf et al., 2006). Colony level infection experiments in the field are now required to demonstrate a causal link between N. ceranae infection and colony collapse.
Nosema ceranae has infected Apis mellifera in Europe since at least 1998 and may be more virulent than Nosema apis
Robert J. Paxton Apidologie 38 (2007) 558–565 Available online