Why did Richard Preston name chapter 15 "the first angel" support your theory

Realy, the reader is left to interpret what or who is an "angel". Recognizing the infection as a filovirus has some very ominous implications. All three of the filoviruses identified thus far have the potential to devastate the human population. There is real cause for concern because several people have now been exposed, and if the virus is growing, or amplifying, in them, they are exposing many more people daily as they go about their lives. The author does not make judgments about their decision, however, and the reader is left to make his or her own determinations of these men's characters.