Rotavirus is just one of the virusus that cause diahorrea - it is fairly contageous through contact with the poo and possibly the saliva. As far as I can remember, it can stay in the system for up to 6 weeks or so and remain contageous during that time.

I doubt it is any danger to the unborn bub, and you should be fine too, it is normally a childhood illness passed on through children in close contact (like childcare or kindy), just be extra vidulant with your hand washing and disinfecting and I think you'll be fine.