Someone else had mentioned the same bug previously and I was confirming that it happened to me. It just seems to fishy that, if pestilence, it would come the same turn as I built the Mercurian Gate and brought Basium into the world.
I tried to compare the effects of Blight with those of Pestilence, but was unable to find any reference material on the two of them.
As I said, my units had just gotten over the Death Damage (about 5 turns) when they got hit with it again. I had not come close to getting over the unhealthy effects in my cities, though, and am sure with 60 unhealthy in a city of 20, for example, all my cities would be pretty much useless for a long time.
If, in fact, it WAS Pestilence which quickly followed Blight, I suppose it is a balance issue rather than a bug and maybe something needs to be added to suppress that event from hitting so soon after the AC event.
I still think it was a Double Blight caused by building the Mercurian Gate, though.
This just happened to me too. It seems that when blight strikes, your units are damaged. I also had this happen twice - Blight occurred, and then a few turns later Basium came into the world, and boom! Blight again.
As for the effects, all but a handfull of my cities shrank to size one and stayed shrunk for at least 20 turns. I do hope this gets fixed - its a real problem.