Board Thread:Metal Gear Solid V/@comment-5.78.86.253-20150920204454/@comment-3131736-20150921023828

Because Quiet was forced to undergo Parasite-therapy due to the injuries she had suffered in the hospital.

The parasites replaced her damaged organs and therefore became so deeply embedded into her that removal became either impossible or would have resulted in her death.

Code Talker also has the parasites in his body which is why he is over 100 years old in TPP.