Coronavirus: From bats to pangolins, how do viruses reach us?
As the deadly coronavirus sweeps across the globe, killing hundreds, halting cruise ships and prompting border closures, scientists race to find out exactly how the outbreak began.
Now, a new study out of China suggests that endangered pangolins — a scaly anteater — are the most likely link between the coronavirus, bats and humans.
While initial speculation pointed to seafood, snakes and another bat-borne coronavirus from Yunnan province in southwestern China, researchers from the South China Agricultural University have found that a genetic sequence of the virus from pangolins is 99% identical to the coronavirus currently infecting some 31,000 people. That means, before reaching humans, the virus was likely passed from bats to the pangolin, the most illegally traded animal in the world.
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At least 630 people have now died from the fast-moving coronavirus, known as 2019-nCoV, which was first detected in December 2019 at a live animal market in Wuhan, China.
What is it about bats?
It isn’t the first time the world has witnessed an outbreak of a bat-borne virus. Ebola is thought to have originated in bats, as well as two other types of coronavirus — SARS (Severe Acute Respiratory Syndrome) which emerged in Asia in 2003 after moving from bats to civets to humans, and MERS (Middle East Respiratory Syndrome), which has infected around 2,500 people since 2012 after being transferred from camels.
This isn’t necessarily surprising considering the great size and spread of the bat population, says Yan Xiang, a professor of virology at the University of Texas. Bats are the second most common mammal after rodents, making up nearly 20% of all species of mammals — there are more than 1,300 species of bat and some can live up to 40 years.
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But experts believe it’s the bats’ unique immune system that allows it to harbor so many viruses.
Bats are a common source of viruses: Ebola, SARS, MERS, and Nipah can all be traced back to them
While Xiang says scientists “don’t yet have a complete picture” of this system, he points to two key elements of the mammal’s immune response, called “innate immunity” — their high body temperatures and higher levels of interferon, which signals the activation of an antiviral state.
Bats are the only mammal with the ability to fly, which increases their body temperature and metabolic rate, and puts their bodies into a constant state of “fever.” Some scientists believe that bats have suppressed their immune systems to cope, which allows them to tolerate more viruses.
Intermediate species
Although the coronavirus is thought to have originated in bats, this doesn’t mean it was directly passed from bats to humans. Coronaviruses are zoonotic viral diseases, meaning they are passed from animals to humans, and while in the animal, the virus goes through a series of genetic mutations that allows it to infect and multiply inside humans.
Pangolins are the most illegally traded animal in the world, and used in traditional Chinese medicine
Xiang is “convinced” of the link between the coronavirus and pangolins, as suggested by the latest study from the South China Agricultural University researchers, who studied more than 1,000 samples from wild animals.
Although this study is yet to be released, Xiang says the evidence for its claims “already exists” in a paper from October 2019, which published genome sequences of sick pangolins smuggled from Malaysia to China, finding evidence of coronaviruses.
This latest novel coronavirus is likely to be “a hybrid of two very similar coronaviruses,” Xiang says — in this case, a mixture of the coronavirus identified in bats in China’s Yunnan province that showed a 96% similarity with the current coronavirus and the coronavirus found in pangolins.
“The virus was probably unable to infect humans directly through bats, so it had to go through an intermediate animal to further mutate in order to infect humans,” Xiang told DW. The intermediate animal that facilitated the hybrid of the two viruses, Xiang says, is “most probably the pangolin.”
Humans defense mechanisms keep us safe — mostly
While the devastation of such outbreaks is difficult to predict, Stuart Neil, head of virology at King’s College London, says “in the grand scheme of things,” events like this “don’t happen very often.”
“We’re probably exposed to these viruses from other species much more often than we get transfers of new viruses from animals and these sustained epidemics,” he told DW.
The reason for that, Neil says, is “due to our intrinsic defensive mechanisms.” There is no such thing as an inherently deadly virus, he points out, because what may be harmless to one species, as shown by the numerous coronaviruses that circulate in bats, may be deadly to another.
“It’s entirely dependent on the defense mechanisms of the host species and whether they can live in harmony with a virus or not.”
Such epidemics are becoming more likely, though, as humans increasingly encroach on the habitats of wild animals, he warns, saying that “humans are exposed to these viruses because of how they behave and interact with animals.”
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Coronavirus: Timeline of the deadly virus in China and worldwide
Pneumonia-like virus hits Wuhan
On December 31, 2019, China notifies the World Health Organization of a string of respiratory infections in the city of Wuhan, home to some 11 million people. The root virus is unknown and disease experts around the world begin working to identify it. The strain is traced to a seafood market in the city, which is quickly shut down. Some 40 people are initially reported to be infected.
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Coronavirus: Timeline of the deadly virus in China and worldwide
New strain of coronavirus identified
Researchers initially rule out the SARS virus, the deadly respiratory illness that originated in China in 2002, killing nearly 800 people worldwide. On January 7, Chinese scientists announce they’ve identified a new virus. Like SARS and the common cold, it is in the coronavirus family. It is temporarily named 2019-nCoV. Symptoms include fever, coughing, difficulty breathing, and pneumonia.
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Coronavirus: Timeline of the deadly virus in China and worldwide
First death in China
On January 11, China announces the first death from the coronavirus — a 61-year-old man, who had shopped at the Wuhan market, dies from complications with pneumonia.
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Coronavirus: Timeline of the deadly virus in China and worldwide
Virus reaches neighboring countries
In the following days, countries such as Thailand and Japan begin to report cases of infections in people who had visited the same Wuhan market. In China, a second fatality is confirmed in the city. By January 20, three people have died in China and more than 200 are infected.
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Coronavirus: Timeline of the deadly virus in China and worldwide
Transmission unclear
Through mid-January, scientists scramble to find out how the illness is being spread among people. Coronaviruses are zoonotic, meaning they are transmitted from animals to people. Some coronaviruses can be transmitted by coughing and sneezing. Airports around the world begin screening passengers arriving from China. On January 20, officials confirm the virus can be passed directly between humans.
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Coronavirus: Timeline of the deadly virus in China and worldwide
Millions under lockdown
China places Wuhan on quarantine on January 23 in an attempt to limit the spread of the virus. Transportation is suspended and workers attempt to quickly build a new hospital to treat infected patients, which total over 830 by January 24, as the death toll climbs to 26. Officials eventually extend the lockdown to 13 other cities, affecting at least 36 million people.
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Coronavirus: Timeline of the deadly virus in China and worldwide
A global health emergency?
More and more cases are confirmed outside of China, including in South Korea, the US, Nepal, Thailand, Hong Kong, Singapore, Malaysia and Taiwan. As the number of infections rises, the World Health Organization on January 23 determines that it’s “too early” to declare a global public health emergency.
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Coronavirus: Timeline of the deadly virus in China and worldwide
Coronavirus reaches Europe
On January 24, French authorities confirm three cases of the new coronavirus within its borders, marking the disease’s first appearance in Europe. Hours later, Australia confirms four people have been infected with the respiratory virus.
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Coronavirus: Timeline of the deadly virus in China and worldwide
Lunar New Year holiday extended
The Chinese Lunar New Year begins with subdued festivities on January 25. Officials cancel many major events in a bid to contain the outbreak, as millions of Chinese travel and take part in public celebrations. By late January, 17 Chinese cities, home to more than 50 million people, are in lockdown. Lunar New Year holidays are extended by three days to limit population flows.
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Coronavirus: Timeline of the deadly virus in China and worldwide
Borders with Mongolia, Hong Kong, eastern Russia close
Cambodia confirms its first case, while Mongolia shuts its border with China for cars and Russia closes its borders in three regions in the Far East. The cost to global tourism is put in the billions and oil prices also plummet. The death toll rises to 41, with over 1,300 infected worldwide — mostly in China. Scientists hope to have the first coronavirus vaccines ready within three months.
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Coronavirus: Timeline of the deadly virus in China and worldwide
Germany braces for virus
On January 27, German Foreign Minister Heiko Maas says Germany is considering evacuating German nationals from Wuhan. There are no reported cases in Germany yet but officials are preparing to fight the virus. German researchers in Marburg are part of international efforts to work on a possible vaccine for the coronavirus. The death toll in China reaches 81, with 2,700 affected worldwide.
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Coronavirus: Timeline of the deadly virus in China and worldwide
First cases confirmed in Germany
On January 27, Germany announces its first known case of the virus — a 33-year-old in Bavaria who contracted it during a workplace training with a visiting Chinese colleague. He is put under quarantine and observation at a Munich hospital. The following day, three of his colleagues are confirmed infected. The death toll in China reaches 132, with around 6,000 infected worldwide.
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Coronavirus: Timeline of the deadly virus in China and worldwide
International evacuations begin
On January 28, Japan and the US are the first countries to evacuate some of their citizens from Wuhan. Four of the Japanese passengers are taken to the hospital with fevers on arrival. Australia and New Zealand say they will also send planes to bring their citizens home. Global cases mount to nearly 6,000 infections, more than the 2002-03 SARS outbreak that killed roughly 800 people.
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Coronavirus: Timeline of the deadly virus in China and worldwide
WHO declares global health emergency
On January 30, the UN’s World Health Organization (WHO) declared coronavirus a public health emergency of international concern in a bid to protect countries with “weaker health systems.” However, WHO Secretary-General Tedros Adhanom Ghebreyesus did not recommend trade and travel restrictions, saying these would be “an unnecessary disruption.”
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Coronavirus: Timeline of the deadly virus in China and worldwide
Wuhan evacuees arrive in Germany
On February 1, 124 people including 102 Germans arrived at Frankfurt airport after being evacuated from Wuhan, the epicenter of the virus, on a German Air Force flight. The evacuees were taken to military barracks in Germersheim where they were set to be quarantined for 14 days. At least two of the evacuees were said to be infected with the new virus.
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Coronavirus: Timeline of the deadly virus in China and worldwide
First death outside China
The first death linked to the novel coronavirus outside of China was reported in the Philippines on February 2. A 44-year-old Chinese man had traveled from Wuhan to Manila before falling ill and being taken to hospital, where he later died of pneumonia.
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Coronavirus: Timeline of the deadly virus in China and worldwide
New coronavirus hospital in just 10 days
The Huoshenshan (Fire God Mountain) Hospital in Wuhan, built in just over a week, opened on February 3. The hospital aimed to use a mix of both Western and traditional Chinese medicine to treat those infected with the coronavirus.
Article source: https://www.dw.com/en/coronavirus-from-bats-to-pangolins-how-do-viruses-reach-us/a-52291570?maca=en-rss-en-all-1573-rdf