A Japanese macaque eats a banana. Credit: UC San Diego
A new University of California San Diego study suggests that humans may not be alone in changing behavior after experiencing a disease threat.
Researchers found that macaque monkeys who had lived through a deadly disease outbreak became significantly more cautious about food that appeared contaminated, even though they did not know how the disease had spread. The findings suggest that pathogen-avoidance behavior can be shaped by experience.
The research grew out of an unexpected event at a Primate sanctuary in southern Texas. In 2020, staff confirmed the presence of simian retrovirus Type II, which can cause an AIDS-like immunodeficiency, in some of the sanctuary's Japanese macaque groups. The virus, primarily transmitted through bites and scratches, caused severe illness and death in some animals. The sanctuary responded by separating groups and implementing strict testing and quarantine measures. This created an unusual natural experiment—three groups had experienced the outbreak while one had not.
The researchers tested 55 macaques to see how they responded to a choice between food placed on a clean wooden surface and food placed on a surface covered with real macaque feces sealed under a layer of clear epoxy to preserve visual cues while removing the smell and any risk of infection.
The macaques from groups that had experienced the outbreak were far less likely to eat the food from the contaminated surface. They ate from what appeared to be a contaminated surface in just 47% of trials, compared with 79% of trials for monkeys from the group that had never experienced the outbreak.
Importantly, monkeys from outbreak-exposed groups behaved similarly whether or not they themselves had been infected. This suggests the behavioral change was associated with having lived through the outbreak, rather than actually experiencing illness.
The findings shed light about the evolution of disgust. Human disgust is often thought to have an important role in protecting us from pathogens. We recoil from feces, spoiled food and other potential sources of infection, and our sensitivity to those cues can change depending on context.
For now, the research offers a new perspective on how living through disease may change how people behave—even after the peak of threat has passed.
Data from UC San Diego