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Oct. 28, 2020, 3:52 p.m. EDT

Even vampire bats practice social distancing when they get sick: study

Animals often isolate to avoid spreading disease in their communities — yet many humans refuse to do so

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By Nicole Lyn Pesce


MarketWatch photo illustration/iStockphoto
Vampire bats self-isolate when they get sick.

While social distancing during a pandemic may feel unnatural to many people, it’s actually quite common in the natural world.

Birds do it, bees do it — and even vampire bats do it.

A new paper published in Behavioral Ecology on Tuesday finds that diseased wild vampire bats spend less time near other bats in their colony — including other sick bats — which slows how quickly the infection spreads through their community.

U.S. researchers noticed that sick vampire bats ( Desmodus rotundus ) kept their distance from other bats in laboratory settings, and they wanted to see whether the bats would also exhibit this behavior in the wild.

So they captured 31 adult female vampire bats from a colony roosting in a hollow tree in Lamanai, Belize. They simulated sickness in the bats by injecting a random half of them with an immune-challenging substance (lipopolysaccharid, or LPS), while the control group of bats was injected with saline. The researchers also attached proximity sensors to the bats, and released them all back into their hollow tree to track any changes in their movements and interactions with other bats.

Their findings: the “sick” bats associated with fewer bats in the group; they spent less time with other bats; and they were less socially-connected to healthy groupmates. “Sick” bats interacted with four fewer bats, on average, compared with the healthy control bats. And “sick” bats spent 25 fewer minutes associating per partner. The healthy bats had a 49% chance of associating with each control bat, but only a 35% chance of associating with each “sick” bat.

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And these limited interactions weren’t just because the “sick” bats were all clustered together; in fact, associations between two “sick” bats were even lower than between a “sick” bat and a control bat. The “sick” bats generally self-isolated to avoid being in close proximity with any other bats. The researchers concluded that this helps “slow the spread of a pathogen that is transmitted at higher probability with higher rates of physical contact (e.g., grooming) or closer proximity.”

Previous studies of vampire bats in captivity have found that bats injected with the same LPS immune-challenging agent to simulate sickness also kept their distance: they slept more, moved less, spent less time grooming neighboring bats or engaging in social grooming, and called out to other bats less frequently. But one study noted that mother bats still interacted with their babies at the same rate, whether they were sick or not, showing that close kin relationships continued in the face of infection, similar to how people will still care for a sick member of their household, or check in on ill relatives.

Read: Social distancing ‘substantially varies’ by income: study

Turns out, social distancing is the animal kingdom’s best line of defense against infectious diseases, since animals don’t have medical treatments or vaccines (not without human intervention, anyway) that people have developed. And social distancing in nature comes in many forms.

Bees and chimpanzees are among the most aggressive. If the foulbrood bacterial disease infects a honeybee colony — which liquefies the honeybee larvae from the inside, yikes — the bees will physically toss diseased members from the hive to protect the rest of the colony. And famed primatologist Jane Goodall observed chimpanzees attacking and ostracizing other chimps who had contracted the highly-contagious polio virus from their troops, National Geographic reports .

Or many species choose to simply avoid members of their community that they can sense are sick. American bullfrog tadpoles in one study actively avoided other tadpoles that they could detect had a deadly yeast infection. Caribbean spiny lobsters can tell whether other lobsters have contracted the Panulirus argus virus, which kills more than half of the young lobsters in infects, by smelling their urine. So studies show that if a lobster doesn’t pass the sniff test, then healthy lobsters will avoid it, even if that means denning by themselves. And while this self-isolation can also leave these highly social animals vulnerable, avoiding the deadly infection outweighs the risk of being alone.

And ants take a two-pronged approach when their colonies become exposed to an infection like the lethal Metarhizium brunneum fungus. Forager ants, which go out in search of food, self-isolate themselves by keeping their distance from the colony while the disease is present — even if they haven’t been infected themselves. Meanwhile, the queen and “nurse” ants responsible for reproduction and protecting the brood, respectively, move further inside the nest and away from the foragers in order to protect these vulnerable members of the population.

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Human society has adopted some of these social distancing measures in dealing with the novel coronavirus pandemic that has infected 43.6 million and killed 1.16 million and counting worldwide, according to Johns Hopkins data.

For example, people have been encouraged to reduce potentially spreading or catching the COVID-19 virus by limiting contact with others through wearing face masks, frequent hand-washing and staying at least six feet away from people who don’t live with them. Especially vulnerable populations such as the elderly and those with pre-existing conditions have been advised to stay home and limit their outside movements to essential errands, like buying food or picking up prescriptions. And schools and non-essential businesses in many areas have been closed temporarily throughout the year, while countries like Spain have put citizens under curfew to curtail surges in infection rates.

But many people across the globe, and certainly across the U.S., have chafed at the measures restricting their movements and activities, even as public health officials have tried to hammer home the message that social distancing is the best weapon we have against the novel coronavirus until we develop treatments and vaccines that are proven to be effective against COVID-19. What’s more, a new study by Imperial College London warns that COVID-19 immunity may only last a few months after infection, further discouraging the idea that a population can develop herd immunity.

Read: Politics around masks, social distancing and vaccines is making America sicker, says former HHS secretary Louis Sullivan

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases for the last three decades, has called for a national mask mandate. And a recent study from the University of Washington’s Institute for Health Metrics and Evaluation suggests that 130,000 American lives could be saved by February if: 95% of people wear masks properly (covering their noses, mouths and chins) in public places; social distancing, handwashing and other non-pharmaceutical precautions are taken; and businesses and schools shut down either partially or completely for six weeks if the daily death is at least 8 deaths per million population.

In the absence of a universal mask mandate, the researchers forecast that approximately 511,000 people total will have died from COVID-19 in the U.S. by February 2021. As of Tuesday afternoon, the U.S. had the highest case tally in the world at 8.7 million, and the highest death toll at 225,765, or about a fifth of the global total.

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