Overview
- A study published Oct. 20, 2026 in Royal Society Open Science found that Japanese macaques from groups that lived through a 2020 simian retrovirus Type II outbreak were far less likely to eat food that looked contaminated than macaques from an unexposed group.
- Researchers tested 55 macaques using fruit placed on a clean surface versus fruit placed on a surface with real macaque feces sealed under clear epoxy so the cue was visible but posed no infection risk.
- Monkeys from outbreak-exposed groups ate from the contaminated-looking surface in 47 percent of trials compared with 79 percent for the unexposed group, and this change appeared whether or not individual animals had been infected.
- A follow-up comparison across rearing backgrounds showed former pet macaques raised by humans were more likely to take contaminated-looking food than sanctuary-reared macaques raised by macaque mothers, pointing to early social learning as a factor.
- The virus spreads by bites and scratches not by contaminated food, so authors say the results show generalised, socially learned pathogen avoidance that may illuminate the evolutionary roots of disgust and could affect how groups respond to future outbreaks.