(I made an account to comment on this ^^') The bubonic plague has a vaccine made for it, antibiotics can easily treat it, there are some recent cases (although we haven't seen epidemics or pandemics of it), buboes are much larger than a simple rash and, if I recall correctly, pox of any kind is caused by viruses. In short - I doubt Yersinia Pestis is involved in avia pox.