Treating hepatitis C in former medical experiment chimpanzees

Kyoto, Japan -- As close relatives of humans, chimpanzees had sometimes been used in biomedical experiments. They were instrumental in the identification of the hepatitis C virus: the then mysterious pathogen was artificially injected into chimpanzees for study, leading to its eventual identification in 1989. Since then, treatments for humans have advanced and hepatitis C can now be nearly cured with medication. However, the same treatment has not been extended to the chimpanzees.

In 2022, a team of researchers from Kyoto University found that chimpanzees infected with hepatitis C had experienced negative health effects and shorter lifespans. This time, in a collaboration with Kumamoto University, the team was determined to eliminate this virus in chimpanzees residing at Kumamoto Sanctuary, a research facility of Kyoto University’s Wildlife Research Center. The sanctuary is home to several chimpanzees who were once used in medical experiments by multiple organizations in Japan, and is a place where they can spend the rest of their lives being cared for.

"Prioritizing chimpanzee health and welfare is the number one reason for conducting this study," says first author Satoshi Hirata. "We felt that it is our responsibility to do whatever we can to improve their condition."

After the team's first study, eight chimpanzees at the sanctuary with chronic hepatitis C infections were still alive. Two crowdfunding campaigns allowed the researchers to purchase the costly medication developed for humans and administer it to the chimpanzees. Before treatment, the team evaluated their liver conditions with blood tests to determine the treatment regimen and duration. Three chimpanzees received an 8-week course of medication, four received a 12-week course, and one needed a 24-week course. The researchers ground the tablet-form medication into a powder and mixed it into steamed sweet potato balls or juice.

Following the treatment periods and then again 6 months later, the researchers collected blood samples to check for the presence of hepatitis C. The results revealed that the virus was successfully eliminated in six chimpanzees but still detectable in the other two, possibly due to mutations associated with drug resistance. Upon completion of the drug regimen the team also thoroughly examined the chimpanzees' livers and found that three had tumors. Unfortunately, two of them subsequently died of liver cancer. But for the chimpanzees who responded successfully to treatment, liver function and health values improved.

This marks the first instance in which hepatitis C virus has been successfully eliminated in chimpanzees for therapeutic purposes. Demonstrating that these medications originally developed for humans have been effective in eliminating the disease in chimpanzees is a major achievement. On a less positive note, this study also revealed the existence of drug-resistant viruses and the development of liver cancer associated with the virus.

"There are still chimpanzees in Europe and the United States with chronic hepatitis C infections, so I hope this study will serve as a catalyst to improve their welfare," says Hirata.

###

The paper "Direct-acting antiviral therapy and hepatocellular carcinoma in captive chimpanzees with long-standing chronic hepatitis C virus infection" appeared on 20 July 2026 in the Journal of Medical Virology, with doi: 10.1002/jmv.71074

About Kyoto University

Kyoto University is one of Japan and Asia's premier research institutions, founded in 1897 and responsible for producing numerous Nobel laureates and winners of other prestigious international prizes. A broad curriculum across the arts and sciences at undergraduate and graduate levels complements several research centers, facilities, and offices around Japan and the world. For more information, please see: http://www.kyoto-u.ac.jp/en