Millions who have read Laura Ingalls Wilder’s Little House books are familiar with the trials and tribulations of Laura’s blind sister Mary. In By the Shores of Silver Lake, Laura attributes Mary’s blindness to scarlet fever: “Mary and Carrie and baby Grace and Ma had all had scarlet fever. Far worst of all, the fever had settled in Mary’s eyes and Mary was blind.” (p 1). Herein, we examine the plausibility of scarlet fever as the cause of Mary Ingalls’ blindness by systematically analyzing biographical documents, local newspapers, school registries, and epidemiologic data on blindness and infectious disease in the years when Mary and Laura Ingalls were children. We conclude that Mary’s blindness was probably caused not by scarlet fever but by viral meningoencephalitis.

Mary Ingalls went blind in 1879 at age 14. Between 1840 and 1883, scarlet fever, caused by Streptococcus pyogenes, was one of the...

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