How was chickenpox first introduced into humans?

Once upon a time,: there was a chicken....Not! The Greeks referred to its latent form as Zoster; the Romans as cingulus, shingles. In the 1600s, an Englishman, Dr. Richard Morton described what he thought a mild form of smallpox as "chicken pox." No one knows why, except maybe his descendants. In 1767, Dr. William Heberden, also English, was the first to demonstrate that chickenpox was different from smallpox.