If you suspect driftwood, you can boil it for about 15 minutes, or soak it in a strong bleach solution, then rinse well, soak again in water that has been treated with a chlorene remover and set it out to completely dry before using it.

Generally however, any diseases and/or parasites that would harm fish are themselves aquatic and if the driftwood was completely dry before you bought it, anything aquatic previously living on or in it, is long dead.