An orthopoxvirus, variola major, gave rise to immunology. Somewhere in Asia centuries ago someone must have made an extraordinary intellectual leap. Presumably, based upon the observation that people who had recovered from smallpox (caused by variola major) never suffered from the disease again, an ancient lateral thinker decided to test the proposition that exposure of a naive subject to scabs from the rash of smallpox sufferers might prevent or alleviate later naturally acquired disease.
Even now, we do not fully understand why deliberate cutaneous or inhalation infection with virulent variola major from scabs should cause infection with much lower mortality than naturally acquired smallpox. However, this first experiment in immunology was so successful that the practice became widespread in India and China for centuries before it reached Europe.
Arno Mullbacher is leader in molecular immunology and virology, John Curtin School of Medical Research, Australian National University