Imagine a world where human beings can be organically enhanced to peak physical strength/ speed/ agility and maybe even gain telekinetic abilities to some extent. This enhancement is caused by the (probably painful) bonding of an alien organism to its otherwise perfectly normal human host.
My questions are:
1) Is it biologically plausible at all to imagine that such a creature could gift its host with such powers? Narratively speaking it seems fair to assume that such a pairing would result in reduced lifespan of the host, but would that even have to apply?
2) How would a parasite have to be attached to create such changes in its host? I thought of some bonding to a human's spinal column, but would that do more damage than good?
3) Just for the sake of cool, I imagined these human hosts to have colored eyes - perhaps different sub-species of parasite would result in different eye colors, thus suggesting variations in ability (red eyes are more physically oriented, blue eyes have greater psychic powers, etc). Again, does this make an iota of sense from a biological point of view? Do parasite-host pairings cause such specific physical changes?