4 scenarios about the origin of the SARS-CoV-2 virus

Direct animal-to-human transmission, animal-to-human transmission through an intermediate host, transmission through frozen food, and laboratory leakage are the four hypotheses about the origin of SARS-CoV-2. reported in the WHO report.
Investigations into the origins of the SARS-CoV-2 virus that causes the Covid-19 pandemic are continuing. The SARS-CoV-2 virus has so far infected more than 172 million people globally and caused more than 3 million deaths.

On May 26, the Biden administration directed US intelligence officials to take a closer look origin of SARS-CoV-2 , including theories such as animal-to-human transmission and lab leaks. The SARS-CoV-2 virus has so far infected more than 172 million people globally and caused more than 3 million deaths. (Photo courtesy: AFP) To date, the most comprehensive look at the origins of Covid-19 is a report by the World Health Organization (WHO) published on March 30 by an international team of researchers who traveled to China to Investigate the origin of the SARS-CoV-2 virus. However, weeks later, many countries around the world have expressed concern that investigators have not had access to adequate data, while scientists say the report clearly shows how the virus develope. “The quick and obvious answer is not possible, as it normally takes years to trace the source of the virus. But in this case, I think we have enough evidence to make some hypotheses about SARS-CoV-2,” said Angela Rasmussen, a virologist at the Center for Global Health Science and Security at the Center for Disease Control and Prevention. Georgetown University Health, said. In the WHO report, the team found that it is possible that SARS-CoV-2 was transmitted from one animal to another before it was transmitted to humans. They also looked at evidence supporting the hypothesis that the virus was transmitted directly to humans from the original host animal, or that the virus spread through the frozen food supply chain. In addition, the research team said that the possibility that SARS-CoV-2 leaked from a laboratory in Wuhan (China) is “very unlikely”. Below are the evidences for each of the four hypotheses about the origin of SARS-CoV-2 that the WHO report makes. 1. Direct animal-to-human transmission WHO assesses direct transmission of SARS-CoV-2 from animals to humans as a “probable” possibility. The SARS-CoV-2 virus originated in an animal, possibly a bat, and then spread to humans. The WHO report provides evidence that the majority of coronaviruses that infect humans come from animals, including the virus that caused the 2003 SARS outbreak. Bats are thought to be the most likely animal to cause it. epidemics of Covid-19 because they are hosts of a virus that is genetically related to SARS- CoV-2. The WHO report acknowledges the possibility that SARS-CoV-2 spread to humans from pangolins or ferrets. However, David Robertson, a virologist at the University of Glasgow, said that the WHO team of scientists had sampled many animals other than bats for study, and the analysis showed that bats are a natural reservoir for the virus. SARS-CoV-2. 2. Transmission from animals to humans through an intermediate host According to WHO, the possibility of SARS-CoV-2 transmission from animals to humans through an intermediate host is very high. In the event that SARS-CoV-2 was not transmitted directly from bats to humans, the scientists believe the most likely hypothesis is that the virus first spread through another animal species, such as a ferret or ferret. pangolin. Unlike bats, these animals are in constant contact with humans, especially if they are raised on farms or during the illegal wildlife trade. If SARS-CoV-2 was initially transmitted to another animal, that could also explain how the virus adapted to harm humans, although Robertson said the virus probably won’t change much. Genome analyzes show that SARS-CoV-2 is a virus specifically adapted to humans, which explains why it can be easily transmitted between pangolins, ferrets, cats and other species. other animals. The WHO report indicates that this is the route that previous corona viruses have taken to infect humans. For example, the SARS virus is believed to have passed from bats to civets before causing an epidemic in humans in 2002. Meanwhile, the virus that causes MERS has been found in camels throughout the Middle East. Daniel Lucey, an infectious diseases specialist at Georgetown University Medical Center, said that the similarities between SARS-CoV-2 and coronavirus families like SARS and MERS are a compelling argument that the strain type This virus can be transmitted in the same way. However, if this hypothesis is correct, it remains unclear what the intermediate host for the transmission of the virus from animals to humans is. The WHO team analyzed samples from thousands of domestic animals across China, all of which tested negative for SARS-CoV-2. Mr. Lucey said that the WHO team did not adequately examine mink raised in China, one of the suspected intermediate hosts. 3. Transmission through frozen food WHO assesses the possibility that SARS-CoV-2 transmission through frozen food is probable. Another theory is that the virus can be transmitted to humans through the cold supply chain, the supply chain that distributes frozen food. In this case, the virus may have originated outside of China but spread into the country through the surface of the food packaging or in the food itself. This hypothesis gained interest in the summer of 2020 after several outbreaks in China. Since then, there has been some evidence that pathogens can survive longer at cold temperatures. However, while cold supply chains may play a role in new outbreaks, scientists say there is little reason to think that is the source of the pandemic. There is no direct evidence that SARS-CoV-2 causes food-borne outbreaks, while Rasmussen noted that SARS-CoV-2 is rarely spread through surfaces. . “It is not an impossibility. This possibility cannot be ruled out. But I think the current evidence is not enough to show that,” Ms. Rasmussen said. 4. Leaks from the lab According to WHO, the possibility of the SARS-CoV-2 virus leaking from the laboratory is extremely unlikely. The most controversial theory about the origin of SARS-CoV-2 is that the virus leaked from a laboratory in Wuhan, where scientists studied coronaviruses in bats. WHO scientists point out that there is little evidence that the virus leaked from the laboratory. An employee works at the laboratory of the Wuhan Institute of Virology (China). Photo: AFP There are 2 possibilities of the SARS-CoV-2 lab leak hypothesis, that is, a researcher was accidentally infected in the laboratory or the researchers intentionally invented a corona virus strain to create SARS. -CoV-2. However, the researchers completely rejected the second possibility that SARS-CoV-2 was created by genetic evidence that the virus arose spontaneously. WHO focuses on the possibility that the virus accidentally escaped from a laboratory where wildlife samples are being studied. Although there have been laboratory leaks in the past, the WHO report indicates that these are very rare. According to the WHO report, there is no record of any laboratory in Wuhan working on a virus closely related to SARS-CoV-2 before the first cases of Covid-19 were diagnosed. diagnosed in December 2019, nor have any laboratory staff reported symptoms of Covid-19. An article by the Wall Street Journal on May 23 stated that three researchers from China’s Wuhan Institute of Virology became ill in November 2019 and were hospitalized with “symptoms consistent with both Covid-19. -19 and seasonal flu. However, Chinese Foreign Ministry spokesman Zhao Lijian on May 25 denied this information. When the WHO report was released in April, Mr. Lucey believed the hypothesis was plausible, although less likely than animal-to-human transmission due to the lack of evidence. Lucey pointed out that there was no forensic investigation of the Wuhan labs. “There really isn’t any way to prove or disprove the lab leak theory based on what is presented in this report,” Ms. Rasmussen said, noting that, to address the issue, A forensic examination of the laboratory is required to find the origin of SARS-COV-2. According to expert Robertson, supporters of the virus lab leak hypothesis argue that SARS-CoV-2 has spread too quickly and effectively in humans to become a virus of natural origin. But if SARS-CoV-2 is a “smart” virus, according to genomic studies, Robertson said, it is not surprising that it infects humans so quickly and so strongly.