Can stress spread like a virus? What Animals Tell Us.

Other researchers are now investigating whether this risk of infection can be observed in the entire animal kingdom.

Scientists hope to learn if stress could go away through channels completely distinct from screeches, squeaks, and raised hackles. What they learn could inform the treatment of animals and shed light on the nature of stress in humans.

The researchers “are trying to understand how these processes can occur simultaneously in different taxa in birds, humans, fish and mice, so that the same phenomenon occurs in very different species that have evolved at very different levels,” says Jens Pruessner , psychology professor at McGill University in Montreal.

You have probably experienced a stress contagion. A friend stops by and spends a few minutes complaining about his work or his partner. Although these are not your problems, you suddenly find yourself breathing faster and feeling a little nervous.

That’s because, as you overheard, your body gave you a quick shot of adrenaline and cortisol — hormones that mobilize energy stores to run, fight, and complete projects on schedule. Stacks of research show that frequent bursts of stress are damaging to the body and reproduction over time.

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Neuroscientist Jaideep Bains studies how stress affects the brain.

In 2014, Bains began studying how stress is transmitted from individual to individual in mice in his lab at the University of Calgary. He found that a stressed mouse releases a pheromone from its anal glands, which is then sniffed by a nearby mouse.

“It kinda makes sense, doesn’t it?” said Bains. “If you think what a mouse would do – it could be out in the field and be chased by a predator and return to the nest.

“A voice signal would probably attract attention, but a silent chemical signal that’s only heard by those very close to you would be a great way to let others know there’s a hazard,” Bains added.

Bains found that neural connections in a mouse that smells stress pheromones change to become identical to the mouse that first experienced the stressor. So the brain of a mouse that smelled a stressed mouse looks like it also sensed a stressor.

Next, “we asked … if a stressed mouse could transfer the information to a second mouse, and if the Mouse could then take it Another Mouse,” said Bains. “And it works wonderfully. The third mouse shows the same changes in its brain.”

This also affects people. Like mice, we sense the fears of others.

“We really see ourselves as individuals having their own experiences,” Bains said. “And we don’t think much about how other people’s experiences and what they’re going through might also shape us.”

Measuring stress in wildlife is difficult outside of a neuroscience lab. Scientists are considered predators by most species, and their mere presence triggers a stress response. Animals leave traces of stress hormones in their feces and feathers, but these aren’t real-time samples. And capturing animals to test their blood hormones is itself a stressful process for animals. However, new technologies make the work easier.

Hanja Brandl from the University of Konstanz in Germany is studying guinea fowl in Kenya using small implanted heart rate loggers combined with solar GPS trackers to observe how stress is transmitted from bird to bird. Findings from similar studies suggest that stressed birds have higher heart rates and, among other things, tend to stay closer to their flocks.

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Brandl and her colleagues also use video camera traps — cameras triggered by animal movement — and machine learning in other studies.

“Knowing who goes where and how often they are fed can indicate stress,” says Brandl.

Machine learning is also giving scientists better data from hours of video. Before deep learning algorithms, Brandl had to stare at videos for long periods of time, evaluating sometimes ambiguous behavior. Now the algorithms pick up tiny nuances.

“By giving the computer thousands and sometimes millions of data points, I’m basically letting the computer decide,” she says.

Scientists have also observed these groups work together to relieve stress in anxious individual members. For example, vampire bats calm down members of their social network by sharing food.

The research is already having an impact on animal husbandry. Studies have shown that calves recover faster after dehorning when allowed to return to their social group, and that chicks benefit from being close to their mother hen after experiencing a mild stressor.

“It’s very understandable. … It’s like a kid having a little accident on the playground. And you’ll definitely be fine with your mother,” says Brandl.

Brandl wrote a review article in the Proceedings of the Royal Society B earlier this year calling for further studies on the transmission of stress in animals.

“Further insights from the study of animal social systems are needed to elucidate the mechanisms and consequences of stress transmission,” she writes. “Identifying the extent to which stress transmission modulates animal collectives represents an important research avenue.”

“Right now we’re just taking the first steps and trying to understand how important the transmission of stress really is,” says Brandl. But with more study and more discoveries, “we can really fine-tune any actions that improve animal welfare in captivity and in the wild.”

Bishop Sand is an audio producer at the Washington Post.