Sure it is worms and not fungus? I occasionally have white fungus grow on my adult marms, but it doesn't harm them.
Either way, this is a great general cure for almost anything exterior, including shell rot:
Take out of aquarium
40g salt w/o iodine to 1 gallon water.
Soak 20-30 minutes
Rinse with freshwater
Put into tank.
Provided the "parasites" are not there anymore, the cray will be fine by next molt.