Shobo the chimpanzee celebrated his cure with a feast of mangoes and other fruits and vegetables. It was a rare moment of joy at Kumamoto Sanctuary in Japan, where Shobo and several other chimpanzees had spent years recovering not just from illness, but from their past lives as medical research subjects.
Chimpanzees share about 98 percent of their DNA with humans, making them close enough to help scientists study diseases. In 1989, researchers deliberately infected chimpanzees with hepatitis C to study the mysterious virus that was sickening people around the world. The experiments helped identify the virus, but the chimpanzees who carried it were left behind when treatments for humans improved.
In 2022, a team from Kyoto University decided that neglect was no longer acceptable. Researchers led by Satoshi Hirata found that the chimpanzees still infected with hepatitis C at Kumamoto Sanctuary were experiencing serious health problems, including shortened lifespans. The sanctuary, part of the university's Wildlife Research Center, cares for chimpanzees formerly used in medical experiments across Japan.
"Prioritizing chimpanzee health and welfare is the number one reason for conducting this study," Hirata said. "We felt that it is our responsibility to do whatever we can to improve their condition."
Eight chimpanzees still carried chronic hepatitis C infections. Modern medications called direct-acting antivirals can now cure hepatitis C in humans with near-perfect success rates, but nobody had tried using them on chimpanzees. The team launched two crowdfunding campaigns to raise money for the expensive drugs, then evaluated each chimpanzee's liver health with blood tests to plan individual treatment schedules.
The researchers ground the tablets into powder and mixed them into steamed sweet potato balls or juice — whatever each chimpanzee would happily eat. Three received eight weeks of medication, four needed twelve weeks, and one required a full twenty-four weeks.
The results, published in the Journal of Medical Virology, brought mixed emotions. Six of the eight chimpanzees were completely cured — the first time hepatitis C had been therapeutically eliminated in chimpanzees. Their liver function improved significantly. But two still had detectable virus due to drug-resistant mutations, and examinations revealed that three had developed liver tumors. Two of those chimpanzees died from liver cancer.
Still, the breakthrough opens a door. "There are still chimpanzees in Europe and the United States with chronic hepatitis C infections," Hirata said. "I hope this study will serve as a catalyst to improve their welfare." At Shobo's celebration, the feast suggested what recovery looks like — mangoes, sweetness, and the quiet dignity of being cared for at last.