I always thought that the "pox viruses" are the largest and most complex viruses known for centuries. The characteristic "pocks" produced by variola virus (Smallpox) gave their name to all forms of infectious disease "a dose of the pox". Smallpox first appeared in China and the Far East at least 2000 years ago: The Pharaoh Ramses V died of smallpox in 1157 B.C. The disease reached Europe in 710 A.D. and was transferred to America by Hernando Cortez in 1520 - 3.5 million Aztecs died in the next 2 years.

In the cities of 18th century Europe, smallpox reached plague proportions and was a feared scourge - highly infectious. Five reigning European monarchs died from smallpox during the 18th century.

I suggest to visit the following site for viruses and history of virology.

click here