31/01/2020
Coronavirus spread: Why blame bats?
You can’t get sick from your dog or cat. But bats are loaded with virus.
It’s well known that animals act as reservoirs of infection for humans. Don’t worry — your pet dog or cat won’t give you the new virus, (and you won’t give it to them), even if it’s been rescued from China. But birds and pigs are carriers of the deadly flu virus. Rodents gave us plague. AIDS came from chimpanzees.
No one yet knows exactly who gave us the mysterious new coronavirus. But in a lineup of likely suspects behind a fast-spreading disease that has sickened more than 6,000 people in 19 nations, evidence points to the oft-maligned bat.
Unlike vampire bats of lore, they didn’t bite us. These bats were minding their own business when they were likely wrested from their caves and trucked to a live meat market in Wuhan, China, the epicenter of the outbreak. Or maybe they were just foraging for bugs around a farm, infecting livestock — which we then ate.
And now, in two research studies published within the last week, the genome of the new human virus was found to be 96% identical to the genome of a bat coronavirus.
While we haven’t found the precise variant that caused the outbreak in humans, “the hypothesis that the virus has originated from bats is very likely,” according to a team from the National and Kapodistrian University of Athens, Greece. Chinese investigators reached the same conclusion.
It’s well known that animals act as reservoirs of infection for humans. Don’t worry — your pet dog or cat won’t give you the new virus, (and you won’t give it to them), even if it’s been rescued from China. But birds and pigs are carriers of the deadly flu virus. Rodents gave us plague. AIDS came from chimpanzees.
While bats are implicated in many awful human viruses, from Ebola to rabies, they’re connoisseurs of coronaviruses, a large family of pathogens that look like a “crown” under a microscope. And they don’t get sick and die.
“In recent decades there has been a great increase in the number of human infections associated with bat viruses,” said Robert Siegel, professor of microbiology and immunology at Stanford University.
“What is the cause of this increase? The short answer is that we do not know for sure,” he said.
There are many theories. There is new awareness of risk, he said, because our ability to detect viruses has improved dramatically.
“Using current molecular techniques, research that might have taken years can now be done in days,” said Siegel.
But there are also new threats – such as growing densities of people, climate change and increased agriculture in once-wild landscapes — that boost the likelihood of exposure, he added.
Bats gave us another coronavirus, called SARS, which in 2003 spread to 26 countries, sickening more than 8,000 people and killing 774. SARS jumped from Chinese bats to civets – weasel-like animals that are sold in Asian food markets – and then to humans.
Ten years later, bats were the source of MERS, a coronavirus that appeared in Saudi Arabia and spread to 27 countries, causing 2,260 illnesses and 803 deaths.That virus jumped from bats to camels, then to humans.
They’re even behind the common cold. First identified in a child with bronchiolitis in 2004, one type of coronavirus is now blamed for 1 to 9% of the common colds each year — and has most likely circulated in humans for centuries.
We’ve discovered that bats are teeming with as many as 200 types of coronaviruses. One out of every three viruses carried by bats is a coronavirus. The second most numerous mammals after rodents, they live in huge colonies in caves — incubators for infection.
As they fly around, dropping f***s, they spread the virus to other species — then to us. Or, if we eat bats, our exposure is more direct.
“If one of these viruses gets into a wildlife market where the chance of one animal infecting multiple people is much higher, that’s where the risk is highest,” said Peter Daszak, president of EcoHealth Alliance, in the journal The Scientist. His U.S.-based nonprofit organization has been studying the origins of viruses in China for 15 years.
He suspects that the source is the Chinese horseshoe bat, a common species named for the pointy horseshoe-shaped protuberance on its nose. China has a long tradition of eating wildlife, especially in the southern provinces of Guangdong and Guangxi.
All this detective work is important, because it could help us reduce the risk of future outbreaks. If the viral jump to humans was a rare one-time event, the outbreak will be more readily contained and controlled, according to Daszak. But there’s also the risk of ongoing danger through repeated “spillover events.”
Researchers are puzzled why bats don’t appear to get sick from all their viruses. The latest research, published last year, found a gene mutation in their immune system that lets them coexist with many disease-causing viruses.
To be sure, lots of other animals can be infected by coronaviruses.
Dogs get Canine Coronavirus Disease – but it’s not linked to the new human strain, according to VCA Animal Hospitals, a chain of 1,000 veterinary hospitals in the U.S. and Canada. It’s a short-lived intestinal disease, spread by eating p**p.
Cats can also be sickened by a coronaviruses, suffering flu-like symptoms. It’s not the human variety, either.
There have been no reported cases of pets getting the new human virus. And there don’t seem to be any cases of people giving the human virus to their pets.
The first signs of the current outbreak came on Dec. 29 in China, when four workers at a large and sprawling Wuhan food market were admitted to a hospital with pneumonia, according to the Chinese Center for Disease Control and Prevention.
When health officials took specimens from the market, they found evidence of the virus in 33 out of 585 samples taken from people at the market and the stalls where meat was sold.
How did the virus get there? Why did it jump between one species to another? Experts don’t know.
“If you think about a bat cave… people don’t go into the cave much,” EcoHealth’s Daszak told The Scientist. “But if you start hunting bats in the cave, and then you bring them into a market live, then the bats are shedding f***s in the market.”
“Or if a bat… starts foraging for insects around a farm like a pig farm, and pigs get infected, or some of the other animals in the farm, then suddenly you’ve got 100 animals infected, (and) you can infect a lot more people,” he said.
“I wouldn’t be surprised if we find out somewhere in the next few weeks that actually the initial exposure was from another animal — it’s bats, then to another animal, then to people,” he said.
Biologically, how do viruses make the leap from animals to humans? It’s because we share similar receptors on the surface of our cells, said Daszak. Viruses bind to these receptors, causing disease.
If we have the same receptor that the virus uses in bats or in camels or in pigs, then there’s a risk of that virus invading us. For SARS coronavirus, the cell surface receptor is shared with humans and bats. Last week, Chinese research reported that the new virus uses that identical cell surface receptor.
Since the human immune is rarely exposed to bat viruses, it can react in an inappropriate and dangerous fashion, said Stanford’s Siegel. A related hypothesis suggests that dangerous viruses from bats may use an unusual mechanism for getting into cells, which can trigger an exaggerated immune response that worsens symptoms.
“Many factors are involved in the emergence of bat viruses in humans,” he said, “and it is unlikely that this one will be the last.”
https://www.mercurynews.com/2020/01/29/coronavirus-spread-why-point-the-finger-at-bats/?fbclid=IwAR1ZqDyxp7ulq4cNqrJepZ973jh9ofc25VC7twsqKFtno7TZpjIvlsIaVks
In a lineup of likely suspects behind the fast-spreading disease that has sickened more than 6,000 people in 19 nations, evidence points to the bat.
