Nosema apis vs. Nosema ceranae: What's the difference?

> It has been suggested that N. ceranae induces significantly higher mortality in honey bees than N. apis, but little is known about their comparative virulence. In this study, we used in vivo infection experiments to study the two parasites’ different virulence (i.e. multiplication rate and infectivity). The outcome of the experiments indicates minor differences in infectious dose and multiplication rate between the two species. Moreover, the mortality caused by N. ceranae was not significantly higher than for N. apis and N. ceranae appeared to have no competitive advantage within host. 

> Our results do not suggest substantial differences in individual level virulence between N. apis and N. ceranae. The high colony level virulence in N. ceranae infected colonies reported from Spain (Higes et al., 2008) may be a regional phenomenon as high mortality in infected colonies are not always present. 

> Thus, other factors than N. ceranae alone, such as associated virus infections, may be complementary to explain high colony level virulence in this parasite. For example, some viruses, e.g. black queen cell virus (BQCV) and bee virus Y, are known to add to the pathogenic effect of N. apis (Bailey and Ball, 1991). 

Eva Forsgren, Ingemar Fries. 2010. Comparative virulence of Nosema ceranae and Nosema apis in individual European honey bees. Veterinary Parasitology

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