“Little House on the Prairie” fans know that Mary Ingalls’ blindness was caused by scarlet fever, but the beloved books might have been wrong.

According to a new study, brain infection was the most likely cause of Mary’s blindness in 1879 at the age of 14, the Inquistr wrote. She was one of the main characters in the books that chronicled the lives of Laura Ingalls Wilder and her family during the 1800s.

It was also made into a hit 1970s television show, “Little House on the Prairie,” which stared Melissa Gilbert as Laura and Michael Landon as Charles.

In the "Little House" series, the family believed scarlet fever was to blame for making Mary blind.

But in a study published Monday 4 in the journal Pediatrics, researchers suggest she was a victim of viral meningoencephalitis, which inflames the brain and the membranes that protect the central nervous system.

Co-author Dr. Beth Tarini, a pediatrician and researcher at the University of Michigan, said she always found Ingalls’s blindness perplexing.

“Since I was in medical school, I had wondered about whether scarlet fever could cause blindness because I always remembered Mary’s blindness from reading the 'Little House' stories and knew that scarlet fever was once a deadly disease. I would ask other doctors, but no one could give me a definitive answer, so I started researching it.”

The Associated Press reports that Tarini was determined to settle the question, and after thorough research she found no documents substantiating that scarlet fever was a plausible cause to Ingall’s loss of sight.

Another one of the study’s authors, Sarah S. Allexan, a medical student at the University of Colorado, spoke about what might have really happened.

“Laura’s memoirs were transformed into the 'Little House' novels. Perhaps to make the story more understandable to children, the editors may have revised her writings to identify scarlet fever as Mary’s illness because it was so familiar to people and so many knew how frightening a scarlet fever diagnosis was.”