It is commonly found in warm freshwater and soil. People get infected when water containing the parasite enters through the nose where it can travel to the brain and destroy brain tissue.
The night Lily Mae fell ill, she complained she had a headache before contracting a fever.
The girl's first cousin, Wendy Scott, told NBC she was seen by a doctor that same night.
"They got it checked out," she said. "There were several viruses going around the school. It was assumed it's a virus because the symptoms are exactly the same, so she went home."
Over the next few days, her condition rapidly deteriorated, the young girl becoming incoherent before being taken to the emergency room.
"She was brought into the emergency room on Tuesday when she woke up unresponsive," Scott said. "She was eyes open, she was there, but she wasn't speaking. Nothing."
According to the Texas Department of State Health Services, the rare brain infection, called primary amoebic meningoencephalitis (PAM), is almost always fatal.