In the fifth book of the Little House series, By the Shores of Silver Lake, Mary Ingalls goes blind due to scarlet fever — but that doesn’t seem to be what really happened:
In the spring of 1879, 14-year-old Mary “was taken suddenly sick with a pain in her head and grew worse quickly. She was delirious with an awful fever. We feared for several days that she would not get well,” Laura wrote. Laura vividly recounted the morning she looked at her sister and saw “one side of her face drawn out of shape.” Their mother Caroline explained Mary had suffered a stroke.
While Mary did slowly regain strength over the following weeks, her vision steadily faded. A doctor delivered the devastating verdict: “The nerves of her eyes had had the worst of the stroke and were dying — nothing could be done.” Charles Ingalls later took Mary to a specialist in Chicago, who confirmed there was no hope of recovery.
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The Pioneer Girl manuscript makes no mention whatsoever of scarlet fever. And in a 1937 letter to her daughter Rose, Laura described Mary’s illness as “spinal meningitis” and “some sort of spinal sickness.” Meanwhile, the pupils’ register at the Iowa College for the Blind, where Mary later studied, listed her cause of blindness plainly as “brain fever.”
After continued analysis, Dr. Tarini published a 2013 study in the journal Pediatrics concluding that the true culprit was almost certainly viral meningoencephalitis — an inflammation of the brain and the membranes surrounding it.
So why blame scarlet fever? Turns out, scarlet fever was a household terror of the era, killing up to 30 percent of the children infected. It was so culturally embedded that it also appeared as a theme in Little Women and Frankenstein.