I use my own for 1. to protect me from the gooby gibs of others, but more importantly 2. to protect others from catching cold sores from me!
With that strain of Herpes you are contagious when you are run down and before the sensation appears on your lips. I don't know for how long the infection remains a threat on a boom mike, but I would not want to be responsible for passing it on.
I'm sure more informed contributors will be able to shed some light, but in the meantime my conscience is clear.