Bats are widely believed to have given the novel coronavirus to humans. But Israeli researchers say they have probably spared us from numerous other diseases, thanks to their largely unnoticed social distancing behavior.
Tel Aviv University scientists have just published peer-reviewed research observing that bats that feel unwell stay “home” in their caves, reducing interaction with other species.
They observed that sick bats also stay away from their peers at the slightest hint of feeling inflammation in their bodies, after making five Egyptian fruit bats sick and following them in a large colony for 72 hours.
The researchers used onboard GPS to track foraging, acceleration sensors to monitor movement, infrared video to record social behavior, and blood samples to measure immune markers.
The researchers concluded that the self-isolating behavior they displayed minimizes the risk of infections “jumping” to humans, directly or via another species.
“We observed that during illness bats choose to stay away from the colony and don’t leave the cave,” said Prof. Yossi Yovel, head of neuroscience at Tel Aviv University. “This suggests that in order to encounter a sick bat, people must actually invade the bats’ natural environment or eliminate their habitats.”
As the coronavirus pandemic prompted lockdowns and social distancing, Yovel’s colleague Maya Weinberg became intrigued by a trait she had noticed among bats.
“They are the most sociable of animals, yet totally defying their character, I had noticed that sick bats often separate themselves from others,” she said.
This is atypical for animals, who have been taught by evolution to try to play down signs of sickness and remain with the group, where they are safer from predators and less likely to go hungry.
To explore the topic she designed her formal experiment, which has now been published in the Annals of the New York Academy of Science. As part of the study, Weinberg and Yovel took five bats and injected them with a pathogen that made them feel unwell.
This is the second study to propose such a theory, coming on the heels of a November study in America that concluded that sick bats “associated with fewer bats, spent less time near others, and were less socially connected.”
Weinberg said that her study addressed certain shortcomings of the previous research, following the bats more closely and measuring their movements to the millimeter.
The Tel Aviv paper comes amid a resurgence of interest in the origins of the coronavirus. The World Health Organization said in March that the virus had probably been transmitted from bats to humans through another animal. This remains the mainstream theory, though a week ago US President Joe Biden ordered an investigation into rival theories, potentially including the possibility of a laboratory accident in China.
“We saw a very clear pattern of the sick bats moving away from the other bats, and actually backing away in reverse gear, as others came close to them,” Weinberg told The Times of Israel. “You can use for bats all the terms we used for humans during the pandemic — social-distancing, self-isolation and quarantine.”
Weinberg and her colleagues wrote in their paper that the sick bats “perched alone and appeared to voluntarily isolate themselves from the group by leaving the social cluster, which is extremely atypical for this species.”
They “ceased foraging outdoors for at least two nights, thus reducing transmission to neighboring colonies,” and their behaviors “demonstrate a strong, integrative immune response that promotes recovery of infected individuals while reducing pathogen transmission inside and outside the roost, including spillover events to other species, such as humans.”