so viruses dont spead :)
all of them
One way is for vaccinations. They use dead or weakened viruses to inject into people/animals so they can form immunities.
they can kill you
Certain poos
If people don't duck their heads the spead of the blades can cut their head off.
spead it
It depends on what you mean. If you mean types of viruses, there are:Virii,Trojans,and worms.
Budding and Lysis.
water
By various ways like by sending viruses.
by spreading bacteria