(In-character now...)
Peeking through the keyhole and watching your transforming parents mate you feel yourself getting more aroused by the minute.
Without really noticing you unbutton your jeans and start stroking your penis slowly. You don't even realize that it has shaped change so it resembles a dog's cock now, complete with a furry sheat. Your slow stroking lets your red slick cock emerge out of your sheat slowly.
Still staring through the keyhole you start to rub along the whole lenght of your transformed cock. Waves of orgasmic rushes trail through your young body.
While you are stroking of your red dogmeat your older brother Bryan is leaving his room. He's transforming, too, and his mind has been nearly completely altered by the virus.
He's naked and his penis has been changed into a dog's one, too. Dark fur is growing all over his body and his barely human eyes glow lustily.
You don't notice Bryan as he gets closer, slowly stroking his own cock out of his furry sheat.
Watching mum and dad do it doggy style you keep rubbing your bony doggy member and enjoy every second of it.
When you lastly notice Bryan's breath upon your neck it's far too late to react to what he's up to. Even if you liked to block his upcomming effords the virus that rewrites your DNA would have stopped you. You are becoming what the infection wants you to be: a sex-crazed dog that will be only up to spread the virus to other humans.
Bryans furry arms hug you by your chest and his breath sounds loudly in your pointy growing ears. His scent translates as pure lust and you gladly accept this, 'cause your own body cries out in a urge to mate, too.
Slowly Bryan pushes you down on all fours. He does not need to say a single word as his scent tells you all you need to know.
While mum and das continue mating and growling one room further, Bryan takes off your jeans.
Your cock screams out it's urge to release itself of it's seed and you start panting as your face extends slowly to form a shepard's muzzle.
Bryan climbs upon your fur spouting back in the end, his doggy cock ainimg at your butthole.
You smell his sex-craziness as well as mum and dad's and even your own arousal.
Then Bryan's cock hits home as he drives his member deep inside of you. It feels incredible and you whimper quietly.
Slowly Bryan starts to push his slick member in and out of you.
Both of you continue transforming, faster now as both of you are engaged in serious sexual action which seems to power up the virus.
Your cock dangles between your hind legs as Bryan continues to mate with you, sending out urges to put it to use... soon...