Firstly, a fairy's affliction with the disease and the degree of infection and mutation can indeed be determined from the pupil;
Secondly, the disease doesn't transmit through regular means such as air or bodily fluids, but through a specific kind of extraordinary mutation;
Link hasn't had the chance to fully understand the exact mechanics, although he thought it exhibited similarities to gene mutations caused by radiation;
Last, from the absence of fear in the new fairies towards the changed rainforest fairies mixed with a hint of expectation, it can be boldly inferred that they may deliberately expose themselves to the infection of the disease.
Considering the Fairy World has been under the invasion of Wizard Palo and had in general been at a disadvantage, with extensive territory lost and devastating casualties.
This was done for the sake of resisting, defending their homeland, and ensuring their continuation.
