plants cannot harbor disease... but they can harbor dormant parasites, bacteria and most deffinately will have SNAILS!
potassium promaginate is the best way to disinfect plants ... as for the exact mixture I'm not sure - I just use enough to get a light purple color in the water.
but it will kill everything living on the plant, and the plant itself if your mixture is too strong or you let it soak way too long... I find it penetrates better than bleach, but it can stain your clothes (well, so can bleach).
but potassium doesn't seem to do much to algae - best bet for that is still bleach, as the bleach kills both the plant and the algae, but the plant, being bigger, can take more abuse than the algae.
since your plants just had a very stressful trip through the mail, I wouldn't subject them to bleach - if you have a QT tank that would be good to put them in for a few weeks and see if any critters come crawling out - otherwise, give them a good stiff rinse in cold tap water - the small amount of chlorine in the tap water should help some in disinfecting.