From late May to early August 1934, Dr. Sawyer again visited yellow fever control operations in Brazil. This included a ten-day trip to the Mato Grosso region to check on several puzzling outbreaks of yellow fever in rural areas, and led to the recognition (by Dr. Fred Soper and others) of a new infection pattern: jungle yellow fever. In this letter, Sawyer described a shorter tour through the interior of several northeastern Brazilian states.. NOTE: The original letter is written on onionskin paper.
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