[@shylarah]
Well....this would be horrible and with how it's dealt with id say probably don't use it but there is the lovely subject of prions
Prions are basically defective proteins that when they 'hit' a normal protein they change it to a prion and create chains. These chains basically destroy the brain....it's what causes mad cow
There is no species barrier
There is no vaccine
Nothing can get rid of it

But it is a good example of a thing that can travel anywhere to any being.

Also my thing is that tetanus in particular requires specific environments. Plants and rust and when in a wound it tends to be deep. Requires a series of shots

Hence why I suggested the flu and the cold. Both are viruses and are human related....there is also other various diseases that can be bad like measles chicken pox and so on that are more human related that could be used. I'd say chicken pox would be very interesting to see in a fae realm....measles is too cruel.