How long have you had the monitor?
What size enclosure is it in?
What are the temps? The humidity?
What other inhabitants are you worried about?
Have you had the sav checked by a Vet? If so have they checked for parasites?
Rule out any husbandry or internal parasite issues.
As for diseases that can pass through a collection - there are some. If he's still not thriving after you've double checked his set up and cleared him on the internal parasites, then you can begin to worry about other potential pathogens.