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Friday, 24 January 2020

Snakes are believed to be the cause of reported coronavirus disease in China

Since late December, a new coronavirus respiratory disease has emerged in China. It has already caused several hundred victims. Now, the new strain of coronavirus baptized 2019-nCoV by the WHO, has spread to several other countries. To better understand the virus, virologists must trace its origin and the animal host through which it first passed before infecting humans. A recent study shows that 2019-nCoV was transmitted to humans in the Wuhan market from snakes.

Snakes - Chinese krait and Chinese cobra - may be the initial source of the newly discovered coronavirus that triggered the onset of a deadly infectious respiratory disease in China this winter. The disease was first reported in late December 2019 in Wuhan, a large city in central China, and quickly spread. Since then, sick travelers from Wuhan have infected people in China and other countries, including the United States.

Using samples from the virus isolated from patients, Chinese scientists determined the genetic code of the virus and observed it. The pathogen responsible for this pandemic is a new coronavirus. It belongs to the same family of viruses as the well-known severe acute respiratory syndrome coronavirus SARS-CoV, and the Middle East respiratory syndrome coronavirus (MERS-CoV), which have killed hundreds of people in the past 17 years. The World Health Organization (WHO) has named the new coronavirus “2019-nCoV”.

What is coronavirus?

The name of the coronavirus comes from its shape, which resembles a crown or a solar crown when imaged using an electron microscope. The coronavirus is transmitted by air and mainly infects the upper respiratory and gastrointestinal tracts of mammals and birds.

Although most members of the coronavirus family cause only mild flu-like symptoms during infection, SARS-CoV and MERS-CoV can infect the upper and lower respiratory tract, causing severe respiratory illness and other complications in humans.

The 2019-nCoV coronavirus observed under the electron microscope. Credits: CDC Chine

2019-nCoV causes symptoms similar to those of SARS-CoV and MERS-CoV. People infected with these coronaviruses suffer from a severe inflammatory reaction. Unfortunately, no approved antiviral vaccine or treatment is available for coronavirus infection. A better understanding of the 2019-nCoV life cycle, including the source of the virus, how it is transmitted and how it replicates is necessary to prevent and treat the disease.

2019-nCoV: an initial transmission from animals to humans

SARS and MERS are classified as zoonotic viral diseases, which means that the first infected patients acquired these viruses directly from animals. This was possible because, in the host animal, the virus had acquired a series of genetic mutations which allowed it to infect and multiply inside humans.

These viruses can now be transmitted between humans. Field studies have revealed that the original source of SARS-CoV and MERS-CoV is the bat and that masked palm civets (a mammal native to Asia and Africa) and camels , respectively, are used intermediate hosts between bats and humans.

This graph shows the origins of the different coronaviruses. The initial strains all come from bats. Credits: Science

In the case of this coronavirus epidemic in 2019, reports indicate that most of the patients in the first hospital group were workers or customers of a local wholesale seafood market which also sold processed meats and consumable animals living.

Including poultry, donkeys, sheep, pigs, camels, foxes, badgers, bamboo rats, hedgehogs and reptiles. However, as no one has ever reported finding a coronavirus infecting aquatic animals, it is plausible that the coronavirus may have originated from other animals sold in this market.

A disease transmitted by bats?

The hypothesis that nCoV 2019 comes from an animal on the market is strongly supported by a new publication in the journal Journal of Medical Virology . Virologists have analyzed and compared the genetic sequences of 2019-nCoV and all other known coronaviruses.

Study of the 2019-nCoV genetic code reveals that the new virus is most closely linked to two samples of bat SARS-type coronavirus from China, initially suggesting that, like SARS and MERS, the bald -mouse could also be behind 2019-nCoV.

The authors further found that the DNA coding sequence for the 2019-nCoV peak protein, which forms the crown of the viral particle that recognizes the receptor on a host cell, indicates that the bat virus may have mutated before infecting people. But when the researchers performed a more detailed bioinformatic analysis of the 2019-nCoV sequence, it suggested that this coronavirus could have come from snakes.

2019-nCoV: it would have gone from the bat to the snake

The researchers used an analysis of the protein codes favored by the new coronavirus and compared it to the protein codes of the coronaviruses found in different animal hosts, such as birds, snakes, marmots, hedgehogs, manis, bats and humans. Surprisingly, they found that the 2019-nCoV protein codes are most similar to those used in snakes.

Snakes often hunt bats in the wild. Reports indicate that the snakes were sold in the local seafood market in Wuhan, raising the possibility that 2019-nCoV has passed from the host species - bats - to snakes, and then to humans at the start of this. coronavirus epidemic. However, how the virus could adapt to both cold-blooded and warm-blooded hosts remains a mystery.

The authors of the report and other researchers must verify the origin of the virus by laboratory experiments. The first thing to do is to find the 2019-nCoV sequence in snakes. However, since the epidemic, the seafood market has been disinfected and closed, making it difficult to trace the source animal of the new virus.

DNA sampling from market animals and wild snakes and bats is necessary to confirm the origin of the virus. However, the results reported will also provide information on the development of prevention and treatment protocols.


RESEARCH ARTICLE:  Homologous recombination within the spike glycoprotein of the newly identified coronavirus may boost cross‐species transmission from snake to human

Wei Ji  Wei Wang  Xiaofang Zhao  Junjie Zai  Xingguang Li

First published: 22 January 2020

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