That's why it is "Directed Panspermia". The ships could protect the bugs on their way, which would be a very long distance and a very long time. Bugs or viruses floating in space (undirected) wouldn't last long.
Let me say right here I didn't think so until a couple of years ago a guy ran an electric current through a strand of DNA.
Also read Penrose's Emperors New Clothes too.
A good case can be made that we are just machines ~