Story highlights Kali Hardig, 12, continues to make progress at Arkansas Children's Hospital

Hardig is walking with assistance during therapy sessions, hospital spokesman says

Amoeba causes fatal brain infection, according to the CDC

Parasite generally found in people who swim in warm, fresh water

A 12-year-old Arkansas girl who was infected with a rare brain-eating parasite continues to improve, Arkansas Children's Hospital spokesman Tom Bonner said Sunday.

Kali Hardig is eating, drinking, smiling and talking, Bonner said. She is even walking with assistance during therapy sessions.

When Kali entered the hospital earlier this summer, she was in critical condition, unresponsive and unable to breathe without the assistance of a breathing tube.

A new photo released Sunday shows the dramatic improvement she has made. In the photo, Kali is sitting up in her hospital bed, smiling.

Kali's doctors have been in virtually uncharted territory as they treat her for the rare amoeba, called Naegleria fowleri. Of 128 known cases in the past half-century, just two patients have survived, according to the Centers for Disease Control and Prevention.

Kali is one of two 12-year-olds who recently contracted the amoeba. Zachary Reyna of Florida died last month of the parasite, even after receiving the same experimental drug that was given to Kali. He contracted the amoeba after kneeboarding in a water-filled ditch by his house August 3, his family told CNN affiliate WBBH.

Naegleria fowleri is found in hot springs and warm, fresh water, most often in the southeastern United States.

Between 2001 and 2010, there were 32 reported cases in the United States, the CDC says. Most of the cases occurred in the Southeast.

The amoeba enters the body through the nose and travels to the brain. You cannot be infected with the organism by drinking contaminated water, the CDC says.

"This infection is one of the most severe infections that we know of," Dr. Dirk Haselow of the Arkansas Department of Health told CNN affiliate WMC about Kali's case. "Ninety-nine percent of people who get it die."

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Dr. Sanjiv Pasala, one of Kali's attending physicians, said they immediately started treating her with an antifungal medicine, antibiotics and a new experimental anti-amoeba drug doctors got directly from the CDC. They also reduced the girl's body temperature to 93 degrees. Doctors have used that technique in some brain injury cases to preserve undamaged brain tissue.

Two weeks ago, doctors checked the girl's cerebral spinal fluid and could not find any presence of the amoeba.

Pasala said that while other cases have not met with such favorable results, what may have made a real difference is that the girl's mother got her to the hospital so quickly.

Willow Springs Water Park in Little Rock is the most likely source of Kali's infection, according to a news release from the Arkansas Department of Health. Another case of the same parasite, also called primary amoebic meningoencephalitis, was reported in 2010 and was possibly linked to Willow Springs.

"Based on the occurrence of two cases of this rare infection in association with the same body of water and the unique features of the park, the ADH has asked the owner of Willow Springs to voluntarily close the water park to ensure the health and safety of the public," the news release said.

The first symptoms of primary amoebic meningoencephalitis appear one to seven days after infection, including headache, fever, nausea, vomiting and a stiff neck, according to the CDC.

"Later symptoms include confusion, lack of attention to people and surroundings, loss of balance, seizures and hallucinations," the government agency's website states. "After the start of symptoms, the disease progresses rapidly and usually causes death within one to 12 days."