In 2020, a serious viral outbreak occurred at a monkey sanctuary in Texas. The virus caused illness and death among three groups of macaques. A fourth group escaped infection.
To see whether the outbreak made the monkeys more vigilant, the researchers set up a test. The monkeys could choose between picking food from a clean surface and one covered with macaque feces. To prevent infection or exposure to the smell, the feces were covered with transparent plastic.
The results were clear. Monkeys in groups affected by the virus ate significantly less often from the dirty surface than those in the unaffected group. Even monkeys in the affected groups that had not been sick themselves became more selective.
The study was published in Royal Society Open Science, and the researchers conclude that the same phenomenon exists among humans.