The American journalist who contracted Ebola while working in Liberia is showing signs of improvement, The Nebraska Medical Center said in a news release Friday.

“[Ashoka] Mukpo’s condition is slightly improved,” Dr. Phil Smith, medical director of the biocontainment unit at The Nebraska Medical Center, said in the news release. “He’s been taking in some fluids and drinking Gatorade. But everyone needs to be reminded that this is still a very serious illness we’re dealing with and no one has a lot of experience treating it.”

Mukpo, 33, is being treated with brincidofovir, the experimental drug by biopharmaceutical company Chimerix, the hospital confirmed Tuesday. 

Mukpo also received a blood transfusion Wednesday from Dr. Kent Brantly, an Ebola survivor who previously donated blood to Dr. Richard Sacra, a Massachusetts doctor who has since recovered from the virus.  

The World Health Organization (WHO) has urged medics to use “convalescent therapies” such as blood transfusions from recovered Ebola patients to treat Ebola patients.

Mukpo’s father, Dr. Mitchell Levy, said on Friday that he was “cautiously optimistic” about his son’s recovery.

“We definitely aren’t out of the woods, but it’s nice to see even a small amount of improvement,” Levy said. He noted that he was grateful for the team of 40 medical professionals caring for his son.

Mukpo previously told his father he wasn’t sure how he contracted Ebola, but that he thought it may have occurred while he was spray-washing something and contamination splashed back on him.

Thomas E. Duncan, the first Ebola patient diagnosed in the U.S., had also been treated with brincidofovir. Duncan, 44, died Wednesday morning.

The drug, which comes in tablet form, is currently undergoing additional tests in laboratory animals infected with Ebola. According to a statement from Chimerix, it was approved by the FDA for use in human Ebola patients on Monday.

The Associated Press and Reuters contributed to this report.