... First possibility: His target, the SCOPE Virus, is infectious even to him, so he used a minion rather than risk infection. Lotusmon specifically, as her Serpent Cure would likely render her able to purge the virus from herself should she become infected.

Second possibility: He doesn't want to reveal himself to us yet. Perhaps because he is someone we know, or at least someone one among us would recognize. Or he fears that one among us would recognize him.