As much as Bryan didn't want to admit it, he was growing increasingly aroused, and Mark's hand around his tail wasn't helping. It felt good..almost too good, the sensation of a simple touch..
"Mark...I.." Bryan stammered,"I donno if you...you should be touching me...it's...it's contagious.."
"I'm not worried, Bryan," Mark replied, rubbing the base of Bryan's spine, where the tail was budding from. Mark stepped in closer, rubbing more firmly, embracing Bryan now.
"Mark...I think...what you're feeling....it's the virus...doing this..." Bryan weakly protested, trying to deny the urges welling inside of him, but having little success. His half-human, half-dog penis began to bulge.
"Buddy," whispered Mark, moving his hand down to massage Bryan's ass, "If that's the virus doing it to me, doesn't that mean I'm already infected?" Mark moved his hand further down and around, toying with the base of Bryan's balls.
"Uhhnn...," muttered Bryan as more fur began to sprout, and his cock emerged from its sheath. Mark moved a finger to Bryan's rectum and began toying with the edge of it as Bryan's canine teeth began to elongate. Suddenly, Bryan was filled with an URGE. Not simply an urge to fuck or be fucked, but to spread the virus, to make more like himself and his family. Bryan spun suddenly, planting a wet kiss on Mark's mouth, a slightly oversized tongue lapping at Mark's face.
Mark took a step back, dazed almost. A brown five o'clock shadow had begun to sprout on his face nearly instantaneously. "Oh...oh..shit..." Mark said," Buddy, you didn't tell me it felt THIS good!" He tugged off his shirt, revealing a tuft of more brown fur blossoming on his chest.
Bryan was more interested in what was going on in Mark's pants, however, and he tugged at the waistband, popping the button fly open in the process. Mark's genitals had undergone a similar transformation to his own, Bryan saw. Bryan felt even more aroused, not sure if it was the changes occuring in him, or some latent gay tendency arising.
Bryan gingerly reached out, touching the sheath, seeing a reddened phallus emerge. "Mmm..." growled Mark, "well...why don't we go out with a bang?" He turned Bryan around, again toying with his anus as Bryan's ears began to flatten and flop.
Bryan dropped to all fours compliantly as Mark adjusted his dog-cock for easy entry. Mark felt his cock completely engulfed in heat as he began to hump madly, reaching around and masturbating Bryan as he did so.
Their changes came swiftly, sped up by the rut, and serenaded by the chorus of the family dogs. Bryan's fingers grew stubby, retracting into paws as a dewclaw sprouted from each leg. His face stretched into a muzzle as he moaned in ecstacy. Mark's body grew bulkier, sprouting a mottled black and brown motif, his head taking on a more squared shape.
Once the orgasms occured, Mark and Bryan were no more...simply a rottweiler mounting a spaniel, the only evidence of their human lives being in the pictures on the walls, and the clothing on the floor.