New Treatment for Hepatitis C in Former Medical Experiment Chimpanzees

A team at Kyoto University has reported a therapeutic breakthrough against hepatitis C virus (HCV) in captive chimpanzees, a species closely related to humans and historically central to early HCV research. Decades ago, investigators used experimental chimpanzee infections to drive the identification of the virus, which was finally recognized as hepatitis C in 1989. While modern human treatments now achieve near-cure outcomes, similar benefits had not been demonstrated for chimpanzees living with chronic infection.

In 2022, the Kyoto group showed that chimpanzees chronically infected with HCV experienced measurable health deterioration and shortened lifespans. Motivated by welfare responsibilities, the researchers initiated a collaboration with Kumamoto University to eliminate HCV in chimpanzees housed at the Kumamoto Sanctuary, a Kyoto Wildlife Research Center facility.

The sanctuary provides lifelong care for animals that were once used in biomedical experiments by multiple organizations. “Prioritizing chimpanzee health and welfare is the number one reason for conducting this study,” said first author Satoshi Hirata, emphasizing the ethical drive behind the work.

Eight chimpanzees with long-standing chronic HCV infection received direct-acting antiviral (DAA) therapy developed for human use. Before dosing, investigators used blood-based liver assessments to tailor treatment duration and regimen. The animals were assigned to 8-week (three), 12-week (four), or 24-week (one) courses, with the tablet medication ground into powder and administered via steamed sweet potato balls or juice.

To determine whether HCV was cleared, the team collected blood samples during the follow-up period and again six months after completing therapy. Six chimpanzees showed successful elimination of detectable virus, confirming effective suppression and clearance of chronic infection under these conditions.

In the remaining two animals, HCV was still detectable at follow-up. The researchers suggest drug-resistant viral variants and mutations may have reduced antiviral efficacy, highlighting a key limitation of DAA therapy in long-term infections.

After treatment completion, comprehensive post-therapy liver examinations were performed. Tumors were identified in three chimpanzees, and two subsequently died from liver cancer, linking clinical outcomes to viral persistence or disease biology even when therapy is attempted.

Overall, the study represents the first documented instance of HCV elimination in chimpanzees for therapeutic purposes, demonstrating cross-species effectiveness of human DAAs. At the same time, it reveals the presence of drug-resistant HCV and the association of chronic infection with hepatocellular carcinoma risk in this captive population.

The findings were published in the Journal of Medical Virology on 20 July 2026. Hirata added that similar welfare-focused efforts may be needed for additional chronically infected chimpanzees in Europe and the United States.