The same knowledge necessary to manufacturing such diseases is also necessary to knowing how to combat them or attenuate them. Besides; synthetic biology is far more capable of producing "superkillers" than this.
According to the article, they were originally trying biotech methods, but then shifted to straightforward selective breeding, which worked better.
I'm woefully underinformed on this topic, but this doesn't seem good at all:
I feel as though I ought provide more commentary instead of just an article dump, but I feel more strongly than that that what I have to say would be obvious or stupid or both, so.