Loosely wrap it in tin-foil and "bake it" in the oven at 250 degrees for about 2 hours. That will kill just about anything in it.
I would suggest you replace the analog thermometers in your enclosure with digital ones with temperature probes and place them at or under the substrate. 4 inches off of the substrate doesn’t tell you what your snake if feeling at the point of contact with it.
Regards,
Steve