Laura Ingalls Wilder's older sister, Mary Ingalls, did not go blind due to scarlet fever. In a report from UPI, dated Feb. 5, the cause was viral meningoencephalitis. This is contrary to the information published in the “Little House” series of books, as well as the television series “Little House on the Prairie.”
Dr. Beth Tarini spent about 10 years researching the cause of Mary Ingalls' blindness. She learned it was unlikely Mary Ingalls had scarlet fever, seeing a rash was never mentioned in the book series or Laura Ingalls Wilder's memoir, “Pioneer Girl.” Tarini is an assistant professor of pediatrics at the University of Michigan.
Laura Ingalls Wilder's letters described Mary's illness as “some sort of spinal sickness.” Local newspapers reported that Mary Ingalls suffered from severe headaches. It is believed that the headaches were caused by the viral meningoencephalitis.
It is believed that Laura Ingalls Wilder stated the cause of her blindness was due to scarlet fever because it was more “relatable to readers.” Creative license was also used for the “Little House on the Prairie” television series. Mary Ingalls never married. She lived with Charles and Caroline Ingalls, her parents, until her mother passed away. She then moved in with her younger sister, Grace Ingalls Dow.
Although an autopsy of Mary Ingalls' body might reveal the exact cause of her blindness, there has been no mention of taking such action.