I think you have to look closer at the circumstances in which viruses become a problem. Martin wrote in 2001:

> Fourteen small (17–60 nm) ribonucleic acid (RNA) viruses are currently known in the honeybee (Bailey & Ball 1991). Normally, these viruses persist benignly and rarely appear to cause colony mortality. 

More recently, McMenamin and Genersch wrote:

> 23 viruses have been reported to infect honey bees worldwide, primarily positive-strand RNA viruses in the families Dicistroviridae and Iflaviridae. In the absence of Varroa many honey bee pathogenic viruses only cause covert infections, which show no clinical signs and have no detectable impact on infected bees or colonies.

> Furthermore, it has been demonstrated that when a feeding Varroa mite is actively infected with DWV, and therefore acting as a biological vector, a bee is more likely to acquire a clinically significant DWV infection from the transmitting mite.   

McMenamin, A. J., & Genersch, E. (2015). Honey bee colony losses and associated viruses. Current Opinion in Insect Science, 8, 121-129.

Many viruses are only infective under very specific circumstances, and have little effect under others. When bees clean combs and equipment, they eliminate much contamination. By the way, we had hundreds of hive irradiated when I worked at the Dyce Lab, to prevent chalkbrood. It won't do any good if the main source of the infection is not the equipment.

PLB

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