Macaques shun food that looks contaminated after disease outbreak

Macaques that lived through a deadly disease outbreak became more cautious around food that looked contaminated, according to a study by researchers at the University of California San Diego. The researchers said the animals did not know how the disease had spread, suggesting their food choices shifted after exposure to others becoming sick and dying.

In the study, researchers tested 55 macaques on a choice between food placed on a clean wooden surface and food on a surface covered with macaque feces. The feces sat beneath a clear epoxy layer, which preserved the visual cue while removing its smell and any risk of infection. The test therefore focused on how the food’s appearance affected the animals’ choices.

The research followed an outbreak at a sanctuary. In 2020, staff confirmed simian retrovirus Type II in some groups of Japanese macaques there. The source describes the virus as one that can cause an AIDS-like immunodeficiency. It does not specify how many animals were infected or give a death toll for the outbreak.

Senior author Federico Rossano, an associate professor in the Department of Cognitive Science at UC San Diego’s School of Social Sciences, said that exposure to other animals becoming sick and dying changed the likelihood of behaviors that could lead to sickness.

The researchers described the macaques as more cautious around food that looked contaminated after living through the outbreak. The study’s authors also reported a separate test involving 54 macaques from seven species.

Those animals had varied rearing backgrounds: some were born in sanctuaries or zoos, while others had previously been used in laboratory research or kept as pets. The account does not provide separate results for those animals or explain how their choices compared with those in the outbreak-related test.

The report connects the findings to human food practices during the early COVID-19 pandemic, when many households wiped down groceries before putting them away. Rossano said the research showed a similar behavior in non-human primates.

The study’s described food-choice test examined responses to a visible contamination cue while excluding smell and infection risk; it does not establish that the macaques understood the disease or its route of transmission.