Hi Waldo
Haven't seen you for a while.
By what I can see, it looks like fungus/bacteria and yes it can spread. There are several different kinds of treatments. I like to try the natural stuff first before I bring out my big guns.
Brookn's Recipe is safe and so far has been proven. If that doesn't work then I use Physan. If that don't work then I use Bayer 3 in 1.