The proper way of saying "Human to Human" is Human to Human. EX. Can a worm pass from Human to Human? No.
Human vs. Human is simply a conflict between two humans.
Opinion. Perhaps this question assumes an unfair generalisation. It is part of the basic human character to be concerned about our fellow human beings. Stories regularly appear in the press about...
yes
of course
Why Pick a Human Probiotic Strain Over an animal Strain
Water As a Human Right
Thom Hartmann on the Nature of Man
The Importance of Caring About Human Rights