Judy, the most important thing you want to sterilize is your cutting tool in between cuts. This is done reduce if not eliminate the transmittal of any virus.
The leaf does not need to be sterilized. I would suggest to dip the cut end of the leaf in plain cinnamon. Cinnamon acts as a fungicide and will help reduce the chance of rot. I do not sterilize my soil and do not believe it is necessary.

Dave

Thanks Dave-
As I'm still a novice here (and I've no problem with sterilizing the cutting tool), what kind of viruses should we be worried about? At some point I'm hoping to propagate to sell, so I'm trying to assimilate it all to create the best possible situation.

Best,
Judy

Judy, the good thing about streps is they are more resistant. The virus most associated with streps to my knowledge would be the mosaic virus. I have not heard of many incidences of it happening among my growing friends over the 6 years I have been growing streps. However, better safe than sorry.

Dave