Reading the posts made here so far, I realized I wasn't the only person who found the humor of this illness just fell flat and came across as silly rather than funny. I also can see Maggie as the vector for this infection, but I wonder if the illness represents something more serious. Perhaps it's the first sign that carrying the Winter Knight's mantel is taking a toll on Harry, in this case by weakening his immune system. Remember, the first time it occurred Harry felt a deep ache in his limbs that didn't fade for several seconds. The mantle should have kept Harry from feeling any pain, even a dull achy one. It's a sign that Harry is starting to run up against his limits.