Diabetes is a noun and it's singular just as Aids is a noun and it's singular.

Is there anyway to make Diabetes or Aids plural though?

Good question, mbrown:

Diabetes and AIDS are nouns like sand and water - they're singular because they're "entities". There aren't "many waters in the sea" - there's a lot of water.

"Entity" style nouns (sand, water, diabetes, AIDS) can be made plural by giving them units (cases of diabetes, grains of sand, gallons of water). And the distinction between the singular entity and the plural units is not only useful for subject-verb agreement, but also for some single-plural idioms:

Singular vs. Plural
Much vs. Many (there is too much water in the pool vs. there are too many gallons of water)
Amount vs. Number (the amount of pollution in the air has grown vs. the number of toxins in the water has reached a dangerous level)
Less vs. Fewer (your car uses less gas than mine does vs. this tank holds fewer gallons of gas than that one does)

One way to think about this distinction is to ask "could I count this"? You can't count diabetes (it's just an entity, so it's singular), but you can count the number of diabetes patients (they're individuals, so they're plural).