Let's hope there is none. But the white fungus that appears from inside the wood has many species, and some are safe while others are highly toxic. It seems to be more prevalent with the blond branchy woods like spiderwood, grapewood, though I have no idea how "accurate" these names might be. After I had an issue with a piece of whatever it was, I stopped buying any wood except the dark brown Malaysian Driftwood; I have never had fungus with this (and I have a lot of it) nor heard of fungus with it.
In my case, within a day of adding the wood to the tank the water became a bit hazy, much like a bacterial bloom, so I though t little of it. But then I spotted that all of the cories were respirating very rapidly. And the wood has this sort of slime on parts of it. I did a 75% water change and took out the wood and scrubbed it under the tap. Fish seemed OK, cloudiness was gone, so next day I put the wood back, and by the end of the day, same issues. This time I did the same but took the wood out and let it completely dry for a few months, then put it in another aquarium. It took about a week before I noticed respiration problems, and patches of this fungus on the rear side of the wood where I couldn't see it. Tossed the wood.
I happened to know a microbiologist thrugh another forum at the time, and I mentioned this and also posted about it. Other members reported similar experiences with "grapewood" and the microbiolgist said this was common with some types of wood but it would take analysis by a microbiologist to identify the fungus species. Her advice was to not use the wood or any similar type.
A couple weeks after this, I happened to be in one of my local stores where the owner knew me very well, and I overheard another customer describing similar problems. I caught the owner's eye and she asked me to join the conversation, and it turned out this customer lost all his cories overnight to similar cloudiness and patches of fungus.