Bio-warfare In Middle-earth

[Inziladun]

Originally Posted by William Cloud Hicklin

Long before Pasteur, people had observed that contact with or proximity to infected people, or objects associated with them, led to contagion. Quarantine was used a thousand years before germ theory! (Farther back than that, WRT leprosy). See also the practice of catapulting the corpses of disease victims into a besieged city, and the infamous if distorted tale of Lord Amherst and his smallpox blankets. (Distorted because it didn't and couldn't work; the smallpox virus can't be transferred that way).

With the plagues sent by Morgoth and Sauron though, there doesn't seem to be any physical medium for the sickness to be transferred to their enemies. The illness came "on the wind".
Contagion as we see it requires an index case for transmission.