Scarlet fever was long believed as the cause of blindness to Mary Ingalls, the sweet sister of Laura Ingalls Wilder, author of "Little House" books.
But according to medical experts, it was not the scarlet fever that snatched off her vision. After analyzing her historical documents, biographical records and other material, doctors have found her suffering from another disease that causes swelling in the brain and upper spinal cord.
During the late 1800s, this illness was better called as "brain fever".
Researchers also explained that in previous decades, scarlet fever was considered quite extensive and fearing. But at the same time, it was often misdiagnosed for many other illnesses related to fever, etc.
In a number of Wilder's letters and unpublished memoir, she has mentioned her sister sick due to "some sort of spinal sickness". During a registry at an Iowa College that was carried out for blind students, it was once again "brain fever" that was stated responsible for destroying Mary's eyesight.
Scarlet fever is generally diagnosed by a red rash which was not mentioned in case of Mary Ingalls. This red rash is due to the germ that causes strep throat. Today, this could be easily treated with antibiotics but during 1800s, no such treatment was available.