Japanese macaques show increased caution after viral outbreak

A study from the University of California San Diego suggests that Japanese macaques develop heightened caution toward potentially contaminated food following exposure to a deadly disease outbreak. Researchers observed this behavior during a natural experiment at a primate sanctuary in southern Texas.

The sanctuary, which houses macaques descended from animals brought from Japan in 1972, experienced an outbreak of simian retrovirus Type II in 2020. This infection, which causes an AIDS-like immunodeficiency, resulted in deaths and severe illness among the population.

In behavioral trials, researchers presented macaques with a choice between food on a clean surface and food on a surface visually marked by feces (sealed under clear epoxy to prevent actual infection). While unexposed control monkeys ate from the marked surface in 79 percent of trials, those that had lived through the outbreak only did so in 47 percent of trials.

According to Federico Rossano, an associate professor at UC San Diego, these findings support the concept of a ‘behavioral immune system,’ where animals change their behavior to avoid infection even without specific knowledge of how a disease is transmitted.