I have never heard of such thing. I know it was not mentioned in any books I've read about Stalingrad and would be a hefty allegation if true. However, I have heard of the source. Kenneth Alibek was a refugee from Russia and has written numerous books about the Soviet weapons program. Even still, he would not have been born during the Second World War and would then would have had to find either sources or heard about such a program second hand.

This would have been a compelling case, however Kenneth Alibek's credibility has been called into question the longer he has been here in America since he left Russia. In an LA Times article they paint him as a man who uses his knowledge to bolster his own pocketbook by selling the threat of biological warfare for his own personal gain. A member of the Bush administration and a former Army General was quoted saying that he "began to think that Ken was more fanciful than precise in some of his recollections."

I am hestitant to believe a single source concerning such a serious allegation. The Russians committed atrocities, however to say they used biological warfare and the source for this has a serious horse in the race to say that they did, seems more "fanciful than precise."

Source: Stalingrad Anthony Beevor Selling the threat of bioterrorism LA Times.