- A coronavirus that originated in Wuhan, China, has killed 25 people and infected more than 830.
- The coronavirus is a zoonotic disease, meaning it jumps from animals to humans.
- SARS, a coronavirus that killed 774 people in the early 2000s, jumped from bats to civets to people.
- The Wuhan coronavirus is also thought to have originated bats, which may have passed the disease to snakes, which then passed it to humans.
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The coronavirus spreading in China and the SARS outbreak of 2003 have two things in common: Both are from the coronavirus family, and both were passed from animals to humans in a wet market.
Coronaviruses are zoonotic diseases, meaning they spread to people from animals. Because wet markets put people and live and dead animals — dogs, chickens, pigs, snakes, civets, and more — in close contact, it can be easy for a virus to make an inter-species jump.
“Poorly regulated, live-animal markets mixed with illegal wildlife trade offer a unique opportunity for viruses to spill over from wildlife hosts into the human population,” the Wildlife Conservation Society said in a statement on Thursday.
In the case of SARS, and probably this coronavirus outbreak too, bats were the original hosts. They then infected other animals via their poop or saliva, and the unwitting intermediaries transmitted the virus to humans.
“Bats and birds are considered reservoir species for viruses with pandemic potential,” Bart Haagmans, a virologist at the Erasmus Medical Center in Rotterdam, Netherlands, told Business Insider.
In the last 45 years, at least three other pandemics (besides SARS) have been traced back to bats. The creatures were the original source of Ebola, which has killed 13,500 people in multiple outbreaks since 1976; Middle Eastern Respiratory Syndrome (MERS) which can be found in 28 countries; and the Nipah virus, which has a 78% fatality rate.
The coronavirus might have jumped from bats to snakes to people
Not all coronaviruses are deadly — the ones endemic to humans, like the common cold, are often considered inconsequential. The coronaviruses that pose a pandemic risk, however, are those that hang out in animals.
“Because these viruses have not been circulating in humans before, specific immunity to these viruses is absent in humans,” Haagmans said.
The coronavirus that emerged in Wuhan has so far killed 25 people and infected more than 830. Experts haven’t yet confirmed the animal species that enabled it to spread to people, but they have some guesses. Scientists in China compared the genetic code of the Wuhan coronavirus to other coronaviruses and found it to be most similar to two bat coronavirus samples.
“There’s an indication that it’s a bat virus,” Vincent Munster, a scientist at Rocky Mountain Laboratories, told Business Insider.
According to a group of scientists who edit the Journal of Medical Virology, the intermediary species in this case could be the Chinese cobra.
That’s because further genetic analysis showed that the genetic building blocks of the Wuhan coronavirus closely resemble that of snakes. So the researchers think a population of bats could have infected snakes, which passed the virus to humans as they were being sold at the Huanan Wholesale Seafood Market in Wuhan.
But the only way to be sure about where the virus came from is to take DNA samples from animals sold at that market and from wild snakes and bats in the area.
Why bats pose such a threat
Bats harbor a significantly higher proportion of zoonotic viruses than other mammals, according to a 2017 study. Experts think that’s because bats can fly across large geographical ranges, transporting diseases as they go. That makes them an ideal host.
Bats pass along viruses in their poop: If they drop feces onto a piece of fruit that a different animal then eats, the creature can become a carrier.
“We know a fair amount of viruses on the World Health Organization’s Blueprint list of priority diseases have either a direct or indirect link with bats,” Munster said. (The list includes SARS and MERS.)
In March 2019, a study even predicted that bats could be the source of a new coronavirus outbreak in China.
“It is highly likely that future SARS- or MERS-like coronavirus outbreaks will originate from bats, and there is an increased probability that this will occur in China,” the researchers wrote.
That’s because the majority of coronaviruses — both those that circulate in humans and in animals — can be found in China. Plus, the study authors said, “most of the bat hosts of these CoVs [coronaviruses] live near humans in China, potentially transmitting viruses to humans and livestock.”
The bat population from which SARS originated, for example, lived in a cave just over 1 kilometer away from the nearest village.
Similarly, a 2017 study warned that “the risk of spillover into people and emergence of a disease similar to SARS is possible.” The authors identified at least 300 separate strains of coronaviruses still circulating in bats.
How SARS, MERS, and Ebola jumped from bats to people
Here are five viruses that likely came from bats, and how the outbreaks compare.
Researchers traced SARS to a population of horseshoe bats in China’s Yunnan province. Humans caught it from weasel-like mammals called masked palm civets at a wet market in Guangdong.
Between 2002 and 2003, SARS killed 774 people across 29 countries and infected more than 8,000. Patients experienced fevers, headaches, and a type of deadly pneumonia that could cause respiratory failure.
MERS, similarly, passed from bats to dromedary camels in the Middle East. That coronavirus circulated in the camel population undetected for decades before jumping to humans in 2012. So far, 858 people have died in 28 countries from the illness, which comes with fever, cough, and shortness of breath.
In southeast Asia, meanwhile, fruit bats were the original hosts of the deadly Nipah virus, which emerged in Malaysia in 1998, then again in India in 2001. The bats passed it to farmed pigs, which gave it to people. Patients experienced headaches and vomiting; many slipped into a coma and died.
Fruit bats in Africa have played a major role in Ebola outbreaks since 1976. The worst Ebola outbreak in history, however, came from a population of long-fingered bats. More than 11,000 people were killed between 2013 and 2016.
How to prevent zoonotic diseases from spilling over into people
At wet markets, the close proximity of shoppers to stall vendors and live and dead animals creates a prime breeding ground for zoonotic diseases.
On Wednesday, authorities in Wuhan banned the trade of live animals at these markets. Officials closed the seafood market where the coronavirus outbreak is thought to have started on January 1.
Experts support this type of intervention to help prevent the spread of viruses.
“Governments must recognize the global public-health threats of zoonotic diseases,” Christian Walzer, executive director of the Wildlife Conservation Society’s health program, said in a statement. “It is time to close live-animal markets that trade in wildlife, strengthen efforts to combat trafficking of wild animals, and work to change dangerous wildlife-consumption behaviors, especially in cities.”
But according to Eric Toner, a senior scientist at Johns Hopkins University, more animal-to-human disease outbreaks are likely to arise, even without wet markets.
“I thought for a long time that the most likely virus that might cause a new pandemic would be a coronavirus,” Toner told Business Insider. “We’re in an age of epidemics because of globalization, because of encroachment on wild environments.”
The Wuhan coronavirus outbreak isn’t considered a pandemic, however. The World Health Organization has so far not declared it a global public-health emergency, since China has quarantined Wuhan and other nearby cities to stop the virus’ spread.
Aria Bendix contributed reporting to this story.