EDITOR—Besides having intrinsic and historical interest, study of a disease throughout history can sometimes yield clues about its aetiology. For example, studies of written records, paintings, and skeletons suggest that rheumatoid arthritis is a relatively new disease in Europe, not appearing there until after the return of explorers from the New World at the end of the 15th century, but having existed in North America for many thousands of years.1 This raises the possibility that some infectious agent from the New World has a role …