"Stronger" and "weaker" in immune terms is fairly subjective, too. It isn't so much that either Cassie OR Tobias has a 'stronger' system. Rather, they are geared to combat different TYPES of diseases.
Cassie might be immune to MORE diseases than Tobias (or vice-versa), but he might be immune to DEADLIER diseases, things that would kill her in a day or two, and still be vulnerable to bird-borne illnesses that she would NEVER encounter or experience, because they aren't communicable to humans.
It isn't comparing apples to oranges. It's more like comparing apples to giraffes.
There is really NO comparison.
Well, there are my two cents.
[By the by, the only reason I can talk on this subject at all: I've committed a great deal of my free time pre-RAF to working at a wildlife rehabilitation centre *irony*, and I was given a half-ream of 'reassurance' information that 'guaranteed' that certain illnesses weren't a personal hazard to the workers.
I learned which diseases were dangerous to each animal with which I worked, and I was thoroughly educated on the dramatic differences between the immune systems of different animals. I did a lot of hands-on work with birds, more than any other animal.
Suffice to say, if you need to know ANYTHING about the digestive, circulo-respiratory, nervous, immune, or skeleto-muscular systems of birds, ESPECIALLY raptors, I am an excellent person to ask.]
