Figure 1.

Distinguishing disease tolerance from general vigor during helminth infection. (A) Graphical representation of a reaction norm (slope of the curve) where, despite similar starting points (P1), Host B has a greater loss in fitness (i.e., increased morbidity) with increasing parasite load than Host A. Thus, Host A displays greater disease tolerance to infection than Host B. (B) Despite differences in host fitness across various parasite loads, the reaction norm between Hosts A and B remains the same. Thus, there is no differences in disease tolerance between A and B, only a difference in general vigor.