Common cold beyond the Ring?

[Bêthberry]

This raises a most interesting question. What is the nature of viruses and bacterial infection in Middle-earth and whence do they arise?

I mean, are they part of the original music and thus part of Eru's plan or are they offspring of Morgoth's thought? Did the doom of men require infection and disease? Decay seems to be part of the negative aspects of Middle-earth--hence Galadriel's effort to maintain Lothlorien free from decay--but aren't bacteria and viruses part of that decay process? Thus, one would assume they belong to Sauron's camp/devising.

Are all illnesses morgul wounds (either lesser or greater)?

Given Elrond's reputation as a healer and Aragorn's 'hands of the King' and Ioreth's remembrance of tribal lore, it would suggest that illness does indeed have a role in the morality of Middle-earth.