Bats carry coronaviruses, but why don’t they get sick?

  • Animals
  • Tuesday, 28 Jul 2020

Bats are thought to be the original host for all coronaviruses, including the one now causing so much pain, but the nocturnal flying mammals might hold the key to defeating Covid-19. — Dreamstime/TNS

In stout metal cylinders chilled to -112°F (-80°C), DeeAnn Reeder and Ken Field store the intestines and other tissues from hundreds of bats.

Little brown bats from the caves of Upstate New York and Wisconsin. Amber-eyed fruit bats from Uganda with white “epaulettes” on their shoulders. From each, carefully labelled bits of spleen, lymph nodes, and lungs.

If that gives you the shivers, the two Bucknell University scientists would counsel you to feel a touch of gratitude instead.

These nocturnal flying mammals might hold the key to fighting the coronavirus.

Bats are thought to be the original host for all coronaviruses, including the one now causing so much pain, yet for some reason the animals do not get sick. Reeder and Field think the secret might be locked in their genetic code.

Starting this month, in a level-2 biosafety lab on Bucknell’s Lewisburg campus (in Pennsylvania, the United States), they and colleagues will carefully thaw 240 samples of bat tissue, treat them with a chemical to deactivate any viruses within, then extract and purify any genetic material for analysis on a supercomputer.

These samples do not have the virus that causes Covid-19, which is thought to have originated in bats in China, but they are expected to contain other coronaviruses – in some cases, more than one variety. Yet when the mammals were alive, they were perfectly healthy, with none of the harmful swelling and inflammation that has felled thousands of the sickest human patients worldwide.

“For bats, it’s almost like these coronaviruses are part of their microbiome,” Field said.

“We’re using the bats as a tool to tell us ‘How do you survive?’” said Reeder.

The idea started in late April, when the pair learned the US National Science Foundation was distributing “rapid” grants for research tied to Covid-19. It turned out the agency was not kidding. The scientists submitted their US$200,000 (RM852,000) proposal on May 7, and got the thumbs-up a week later. A lab technician already has been hired, and at least two Bucknell undergraduates will join the effort as well.

Reeder and Field are professors in the university’s biology department, but with very different backgrounds. He’s a lab guy, with expertise in immunology, while she is happiest in the field.

Reeder, an ardent conservationist, has been trekking to Africa every year since 2004, first to South Sudan, more recently Uganda, studying bats, chimpanzees and elephants in their natural habitat. Among other projects, she assembled a team of citizen scientists to analyse the output from automated, remote cameras in a South Sudan game preserve – a half-million images to date.

Bats are her special favourite, because of their unique physiology – they are the only mammals that fly, of course, but that’s just the start – and the fact that they are easy to study. She can catch them in a net, extract a tiny blood sample, and send them on their way. And while she realises many people view the animals with distaste, she is dazzled.

“Some of them are strikingly beautiful, ” she said, placing the “epauletted” fruit bat in that category. “Some of them are so ugly that only their mothers would love them.”

The African bats in the new study were collected for an earlier study of the mammals’ immune response, including a quest to see if they might harbour the Ebola virus. (They did not.) The North American bats in the Bucknell study originally were collected for research on white-nose syndrome, a fungal disease. While bats seem to coexist easily with a wide array of viruses, the fungus has somehow outwitted their immune systems, killing them by the millions.

The scientists euthanise the animals sparingly, preferring to study them alive in the wild. Those that get sacrificed are seen as a precious resource, preserved with liquid nitrogen in case they prove useful for future experiments.

That was the case for the new study. While coronaviruses are not known to infect the lungs of bats, as they do in humans, the microbes can infect the gastrointestinal tracts of both species. So Field and Reeder immediately thought of all their bat intestine samples in storage, and realised that they compare the same organ in the two mammals – ideally figuring out why the virus could inflame one but not the other.

Physicians have sought to quell harmful inflammation in human Covid-19 patients by treating them with steroids. But those are broad-based drugs that can suppress the immune system – an approach that could backfire for someone fighting an infection.

Bats, on the other hand, are thought to employ a more targeted approach, their bodies producing some sort of internal substance that tamps down inflammation without making the animals susceptible to a virus, Field said. The genetic analysis will reveal two things: which viruses are in the bat samples, and which “pathways” have been activated to keep inflammation under control.

If humans share anything like that pathway, the research could guide the way to a treatment.

Then again, bats are very different. One theory for why they can harbour many viruses with no ill effects is called “flight as fever.” They fly for hours at a time at night, expending so much energy that their body temperatures rise several degrees, possibly keeping viruses in check as a result.

In order to fuel these demanding aerial excursions, some bats eat close to their body weight in insects every night, Reeder said.

“It’s like me having 500 quarter-pounders every night, ” she said.

Field, her research partner, is not so sure fever is the answer. He thinks bats may simply have co-evolved with coronaviruses over thousands of years. The viruses engage in self-selection, “finding” a host that allows them to reproduce. If the bats died, the virus could no longer spread.

“Both the pathogen and the host adapt to each other, ” he said. “Then, when the virus jumps from bats to another host that hasn’t had that co-evolutionary history, the immune system responds in a way that’s inappropriate.”

Like what has happened in humans. Scientists still do not know how that jump happened with the new coronavirus, but the thinking is that it passed through an intermediate host. The original theory, that it originated at a live-animal market in Wuhan, has now been discredited, as some of the first Chinese patients had no connection to that market. Reeder speculated that it might have happened at another market.

But she does not blame the bats for spreading disease. She blames humans for interacting with them.

“When spillover happens, it’s always because of human activity, ” Reeder said. “Spillover is a human problem, not a bat problem.”

On occasion, people wary of infectious bats have tried killing the animals, with disastrous results. In one such case, a new colony of the mammals came back, bearing higher levels of the virus in question, she said. And ecologically, getting rid of bats is a disaster, as they play a crucial role in nature by eating insects and distributing seeds.

Bats are our friends, she said. And if Field and Reeder are successful, they just might teach us how to ward off the next pandemic. – Tribune News Service/The Philadelphia Inquirer/Tom Avri

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Bats , coronaviruses , Covid-19


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