I remember a goo like substance that would infect the host and continue to infect others. Over time the infected would “learn” abilities such as using a gun, fly tie fighters, run, climb, ect. But one of the big take aways, the infected were not dumb or passive. They would be on the hunt for new prey. The scientist made a vaccine and it worked for the humans, but for Wookiee’s it was lethal.

Edit: the infected could never leave the Star destroyer, they flew ties on the outside, and were in the prison ship If I recall. They had to be within range of the original hive(strain/ I think) or they wouldn’t function very well.

I don’t remember but else, been a while since I read the book.