please help identify what is wrong with this cat? mange?

this is a free-roaming cat that hangs out around my place of work, i've known him for months now 

he seemed relatively healthy before now, although underweight 

i just noticed he's developed these weird spots on his shoulders 

they're discolored (whitish) the hair is thinned out and it almost looks like mold on his skin

i used to pet him all the time and now i'm afraid to touch him for fear of contaminating myself and my own housecats

please help me identify what is wrong with this cat and if there is anything i can do for him or if he needs to be seen by a vet right away 

Gosh, Ive never seen mange look so symetrical before.  Honestly, I've never actually seen mange before, only pictures, but I've never seen picture of it looking like that either.  To me, it looks like he's rubbing against something trying to get in and out of somewhere that's a tight squeeze.  A REALLY tight squeeze. 

Hopefully someone else will come along shortly and give their two cents.  @Snooshy had to deal with mange last year, maybe she can be of some help.