Mark begins to crouch down to relieve his friends boner when he started to feel weird. Seconds later he way laying on his side holding his stomach as his body was racked with pain. It was almost as if his body was trying to fight the virus he thought to himself as the weird and painful sensation coursed through his body.
Bryan panted as he watched his friend Mark lay on the floor in pain. His own cock was slick with precum at this point and jumped as he saw his friend starting to gain some canine features. Blond fur was pushing out of his once smooth chest and ass as well as his cheeks.
Mark moaned in pain as his uncut foreskin attached to his groin slightly as it separated from his growing dick, allowing the skin to be pulled back fully. The mushroom tip began to take on a point as his face started to push forward. behind him, his tail bone was pushing on his skin from the inside wanting to be released.
Suddenly the pain ceased and the changes stopped all of a sudden. Standing he went to a mirror and checked out his body. He could still pass as a normal human albeit a hairier one than he started. His face had barely pushed out any, and you could only tell the difference if you had seen him before. Looking down at his now soft cock he could see what was to have been the beginning of his sheath. His foreskin, when pulled down, no longer stopped after uncovering the head, but pulled all the way to the base of his dick. At the base about an inch of the foreskin was now attached to his groin, hidden in his thick pubes. He released his now slightly fuzzy foreskin and watched it move back across his dick and cover the now very slightly pointed tip. Turning around he could see his hairy ass, the skin above it protruding more than it used to as his tail bone had added a few links but not enough to emerge from his skin. Mark had a good guess that his body was somehow able to fight off and build an immunity toward the virus before it could change him much.
Pulling his attention away from himself Mark looked back toward Bryan and smiled as his new dog was sucking himself off. Gears cranked in his head and wondered if there would be a way to pass the immunity to others...