When I was developing tests to detect bioweapons we considered making a test for Ebola. We decided against it because by the time you are contagious it is very obvious that you are sick and in such bad shape you cannot easily move about infecting other.
What if you had one jihadi as a virus source, and some uninfected people extracting body fluids from the source and spraying the fluids on objects in public spaces (handrails, etc?). The guy who was already sick simply has to lie in bed dying. The people doing the spraying will likely die in a month, but while active, they are 100% healthy and symptom free.