In Laura Ingalls Wilder’s semi-autobiographical Little House book series, her sister Mary became ill with fever and severe headache. “Far worst of all, [scarlet] fever had settled in Mary’s eyes, and Mary was blind,” the author wrote.
Yet it was viral meningoencephalitis (a viral brain infection) that caused Mary’s illness and subsequent blindness—not scarlet fever, according to the current edition of Pediatrics. The authors based their conclusion on archival records and medical information.
The new diagnosis is reasonable, based on Mary’s symptoms. Encephalitis commonly causes fever and severe headache, and weakness of the face can be the result of inflammation of nerves from the brain (cranial nerves) related to encephalitis. The outcome of viral encephalitis varies widely, ranging from complete recovery to fatality. Patients may recover, but with an isolated long-term injury to the nervous system that causes deafness or blindness.
As the authors of the Pediatrics study point out, scarlet fever in children today is much milder than it was in the 1800’s. Scarlet fever is caused by the bacterium Group A Streptococcus, which causes strep throat. Certain strains produce a toxin that causes the red, rough rash that characterizes scarlet fever.
Generally, children with scarlet fever are no more ill than children who have strep throat without a rash. But in the 1800’s, scarlet fever was frequently fatal. The availability of antibiotics doesn’t explain the change in the disease’s severity because scarlet fever became milder even before that. The reasons for the change in severity remain unknown.