CCTV News:In 2002, SARS was first discovered in Guangdong, China, and gradually spread to Southeast Asia and even the whole world, which triggered a global epidemic of infectious diseases. It has been 15 years since the first SARS case was reported in December 2002. Where is the source of SARS virus? Recently, a scientific research achievement has attracted the attention of the scientific community: experts from Wuhan Institute of Virology, Chinese Academy of Sciences discovered a natural gene bank of bat SARS coronavirus in Yunnan, China, and the research revealed the possible recombination origin of SARS virus.
The SARS epidemic broke out in 2002, and two years later, that is, from 2004, the research team began to pursue the source of the epidemic, which was 13 years. How is the host of the virus source locked in bats? Finding the possible recombinant origin of SARS virus means that the source of SARS virus has been found? Get close to this research team, uncover the secret of the source of SARS virus, and explore the scientific process behind finding the source of SARS virus.
SARS (Severe Acute Respiratory Syndrome), the epidemic situation announced by WHO, showed that from the end of 2002 to August 2003, SARS spread to 32 countries and regions around the world. There were 8422 cases of infection and 916 cases of death worldwide, with an average mortality rate of 10 .8%. In 2004, when the deadly epidemic finally subsided, the research on the traceability of this unknown virus began immediately.
Shi Zhengli, a researcher at Wuhan Institute of Virology, Chinese Academy of Sciences, and the research team of emerging viruses led by her, also started the traceability research of SARS virus at this time. Soon, the researchers detected SARS coronavirus from civet cats in the wild animal market. However, further experiments show that civet cats are the direct source of infection, but they do not seem to be the "initiators".
Hu Ben, Assistant Researcher, Wuhan Institute of Virology, Chinese Academy of Sciences: "The most direct source of infection is it the most fundamental source? This is not necessarily the case. So in order to find the fundamental source of this virus, we need to find its natural host. Finding its source can fundamentally prevent this disease. "
Hu Ben, an assistant researcher, is responsible for the genetic evolution of the virus. The natural host he mentioned must carry the virus for a long time and not get sick by itself. In addition, in the natural state, these natural host animals must have a certain group infection rate. However, by investigating farms and wild civets, the results are surprising. So, where did these deadly viruses come from? Who is its natural host? Some experts put forward a bold idea.
For scholars who study viruses, bats have a special position. Among mammals, it is the second largest group after rodents, and its species account for 20% of the number of mammal species, which is widely distributed in the world. Bats are also natural hosts of many viruses, including Ebola virus, Marburg virus, rabies virus, Hendra virus and Nipah virus. Because of the bat’s special immune system, it rarely shows symptoms when it carries the virus. In the long course of evolution, bats have become the natural hosts of hundreds of viruses.
In the 1990s, there were two kinds of serious zoonotic viral infectious diseases, which broke out in Australia and Southeast Asia respectively, and both originated from the same animal — — Bat. This puts forward a possibility for the research team tracking the source of SARS virus, whether the source of SARS is also bats.
By detecting 408 bats belonging to different families and genera for antibody and nucleic acid monitoring, the target was gradually clear, and finally a coronavirus similar to SARS virus was found in the bat. Juglans bat, named after its horseshoe-shaped nose leaf with complex structure, is an important host of many animal-derived viruses such as rabies. This discovery was published in the international authoritative academic journal Science that year, which attracted much attention.But soon, the question came again. "S gene", also known as spike protein gene, is responsible for the combination of virus and receptor. When a virus infects a cell, it must first combine with the receptor on the cell surface before it can invade the cell and cause infection.
Bats lie in the daytime and come out at night. In the evening, the researchers will go into the bat cave armed to the teeth or set nets at the mouth of the cave to catch bats. When they come back, they will take virus samples overnight on a makeshift workbench in the wild. Despite wearing gloves, the risk of being bitten by bats still exists.Bats carry a variety of virulent viruses, including rabies. Therefore, before each field sampling, the team members will inject rabies vaccine in advance. Wherever they go, they always insist on non-invasive sampling. Minimize the damage to bats and habitats.
These samples were taken back to the laboratory and stored in a freezer at-80 C.Until 2011, the S gene of SARS-like coronavirus, which is more similar to SARS virus, was detected for the first time in a bat cave in Yunnan. In 2013, the laboratory of Wuhan Institute of Virology, Chinese Academy of Sciences, isolated the first live bat SARS-like coronavirus from samples, and the S gene was similar, which enabled this virus to use the same receptor as SARS virus and infect human cells. It was named "WIV1" after the English abbreviation of Wuhan Institute of Virology to show the important value of this discovery.This achievement was published in the November 2013 issue of Nature. The "key" was finally found. But this small cave reveals more secrets than researchers expected.
The successful isolation of WIV1 has made the differences and debates on the origin of SARS virus "tend to be consistent" among scientists all over the world. The goal of this long-term pursuit has become clearer — — SARS coronavirus originated from the bat.After years of hard work, the source of SARS was finally traced, but scientists did not stop, because there were more secrets hidden in this bat cave where S gene was first discovered.
By comparison, the SARS-like coronavirus found in bat cave has the highest similarity with SARS virus, which is highly homologous. Genetically, this means that the most direct ancestor of SARS virus comes from these bat viruses. Experts said that although no virus exactly the same as SARS virus has been found at present, this discovery fully confirmed that SARS virus originated from bats and revealed its possible production mode — — Gene recombination.
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