Macaques showed increased food aversion after viral outbreak, study finds.

A team of scientists led by UC San Diego cognitive researcher Stephan Kaufhold found that macaques who lived through a viral outbreak at a Texas sanctuary became markedly more averse to eating food placed on simulated feces, the study published in Royal Society Open Science shows. The researchers offered 100‑plus monkeys a choice between a grape on a clean wooden block and a grape perched on a piece of macaque poop encased in epoxy; monkeys that had been exposed to the virus ate the “dirty” grape in only 47 % of trials, compared with 79 % of those that had not.

The experiment was prompted by the wave of germ‑avoidance behavior that swept the United States during the early months of COVID‑19, when people scrubbed groceries, quarantined mail and shunned any surface they thought might carry the virus. Scientists have long known that many animals instinctively steer clear of feces and other disease‑laden material, but it was unclear whether that avoidance could be sharpened after a disease outbreak. In 2020, the sanctuary’s macaques were hit by an SRV infection—an HIV‑like virus that can kill within weeks or cause chronic immune failure—prompting staff to separate the group into individuals who had seen the disease and those who had not.

To test the monkeys’ willingness to take a risk, Kaufhold’s team presented each animal with the two grapes in almost 200 trials between 2022 and 2024. The “clean” grape was always placed on an unmarked piece of wood, while the “dirty” grape sat on a glossy, epoxy‑coated pile of macaque feces designed to look unappetizing but not pose a health hazard. The stark contrast in choices suggests that the experience of a deadly outbreak heightened the monkeys’ disgust response, making them less likely to gamble on a potential source of infection.

The findings hint that disease‑avoidance instincts are not fixed but can be shaped by recent experience, a lesson that may inform how humans and wildlife respond to future epidemics. If animals can learn to be more cautious after an outbreak, similar behavioral shifts could be encouraged in people through targeted public‑health messaging, potentially reducing the spread of new pathogens.