There was once a man that made 'rat' posion that became quite popular In a world far far away (to most who are reading this). It was a man-made virus made by a man who hated cat. He called it rat posion and market it in a contry with barly any regulations. It acted fast on small rodents and by the time they relize it was actually targeting cats, it was too late. Many small and meduim mamanuals started to grow sick and die. Most of the world did not bother to act for most no longer cared about the animals.
It was when they humans started to fall ill that they called it the mammalian extinction virus out of panic. For a few years they tried to work together to solve it, but it grew costly and people started giving up hope. Some people in power begain waring with each other under the guise that they could unite the world against the problem. This divided the world more since may of these men thought genocide(of man and beast) would help kill off the virus.
In the end they seem to lead to their extinction themselves. Over thirty years many common mammalian still lived. The virus evolved to allow their hosts to live long enough so it did not die out with them.