The Hot Zone part 3

During the third part of the book I found it surprising that none of the animal caretakers actually fell ill from Ebola itself.  Although, at the beginning when Milton Frantig got sick I thought he had caught the virus.  What   I learned in the third part was that it is no simple task to decon a building.  All the work that just went into preparing for the decon would have been exhausting, but I found it interesting how they used disinfecting crystals during the procedure.  What I want to know the most is how come no humans got sick from the virus when they actually had it in their systems?