> >Wouldn't longer winters, more consistent cold without cleansing flights account for much greater spore accumulation the individual bee and colony.

Recent work at USDA indicates an age correlation:

> Our studies showed that the Nosema spore load and infection prevalence varied among the different types of adult workers, and both of them increased as honey bees aged: No infection was detected in emergent bees, nurses had a medium spore load and prevalence, while foragers were with the highest Nosema infection level and prevalence.

> During our field survey to assess disease distribution and prevalence in honey bee field colonies, we often found that the status of Nosema infection in honey bee colonies could change from a high prevalence in 1 month to partial or complete disappearance after a few months without treatment.

Li, W., Evans, J. D., Li, J., Su, S., Hamilton, M., & Chen, Y. (2017). Spore load and immune response of honey bees naturally infected by Nosema ceranae. Parasitology Research, 1-10.

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