Why it’s so difficult to trace the origin of COVID-19

That is why scientists support a thorough evidence-based investigation into the origin of COVID-19. However, similar surveys during past epidemics have taken months or years to answer, and in some cases the mystery remains unsolved.

“Science takes time,” says Arinjay Banerjee, a virologist at the University of Saskatchewan, Canada. “It’s a difficult task to go back and confidently identify the source.”

Earlier this year, a team of international World Health Organizations visited Wuhan, China, to evaluate the evidence China provided for the origin of SARS-CoV-2. In a report summarizing their findings, WHO suggested that the virus could be “very likely” to spread from the first infected bats to humans via intermediate host animals.

This was the case of the 2002 SARS-CoV outbreak —The first pandemic of the 21st centuryThe virus spilled from horseshoe-shaped bats in Chinese caves to palm civets sold in the live animal market, where it is likely to infect humans. Similarly, the 2012 MERS-CoV epidemic was suspected to be caused by bats, which later became infected with dromedary and humans.

The WHO report also considered a laboratory leak from the Wuhan Institute of Virology, known for its coronavirus research, to be “very unlikely.” However, the conclusion has sparked a backlash from scientists and governments around the world. They argued that it was too early to rule out laboratory leaks based on the evidence at hand. Other experts warn that political motivation can rush people to conclusions.

“There is a precursor virus somewhere and we need to look for it,” said David Morence, senior epidemiology advisor to Anthony Fauci, director of the National Institute of Allergic Infectious Diseases. It goes from doing due diligence to wasting time and getting hooked. You may have already seen that point. “

Here’s what we know about scientific research into the causes of pandemics and what we still need to do to find a clear answer.

What evidence do virus detectives seek?

Tracking the origin of a virus requires extensive fieldwork, thorough forensics, and considerable luck. The painstaking effort can take years before scientists get the evidence they need to point out the source.

In the case of animal-derived disease, the evidence is usually a genetic match between the viral sequence obtained from the animal and the viral sequence obtained from some of the first identified patients. The match may not be 100% because the virus collects mutations and new genes as it jumps over the host over time. However, after extensive research, scientists have found more than 99% or more complete agreements on some viruses, including the one that caused the two previous coronavirus outbreaks. ..

Palm civet that lives in a tree like a cat. Considered a delicacy, Street market quickly became the focus During the outbreak of Severe Acute Respiratory Syndrome (SARS) in Guangdong Province, China, from 2002 to 2004 Over 8,000 cases and nearly 800 deaths in 29 countries.. Some of the first SARS cases included several infected restaurant chefs dealing with a variety of animals. Blood tests from animal vendors in the region showed a higher prevalence of antibodies to the SARS-related coronavirus compared to healthy controls. The highest level recorded among those who traded primarily on palm civet..

The 2003 paper also included a palm civet nasal swab obtained from the live animal market in Guangdong Province. 99.8 percent match Between the entire genome sequence of SARS-CoV-like virus isolated from civet and the virus from humans. This indicates that the SARS-CoV-like virus has recently infected civets on the market.

However, it became clear that these furry mammals were not the original source, as was the virus. Almost never found in farmed palm civet Before it hits the market, and it’s Not widely circulated in its wild population.. Given that bats carry other zoonotic viruses, researchers suspect that bats are natural reservoirs, and researchers have found bat blood, feces, and throat cotton sticks throughout China and in Hong Kong. Was sampled.

More than a decade later, they identified a horseshoe-shaped bat carrying a strain of virus in a remote cave in Yunnan, southwestern China. Including all genetic parts It is recorded in the viral genome from human patients. The strain that caused the 2002 epidemic Recombinant product Of the various genetic strains found in these bats.

Scientists later used lessons learned from tracking the origin of the SARS virus to investigate the source of the 2012 Middle East Respiratory Syndrome (MERS) coronavirus. Infects more than 2,000 people in 37 countries When Killed nearly 900 people..

The virus First isolated From a 60-year-old businessman who died of severe pneumonia and multiple organ failure in June 2012 at a hospital in Jeddah, Saudi Arabia. Early efforts to track bat-focused sources. In Saudi Arabia, throat swabs, urine, feces, and blood samples from wild bats, including those that occurred in the area where the first patient lived and worked, Coronavirus like MERS in one Egyptian tomb bat fecal sample.. However, without the complete genomic sequence, the role of bats could not be assessed.

in the meantime, Case report It was suggested that some patients were exposed to dromedary or goats. NS 2013 study Antibodies to MERS were found in blood samples collected from retired racing camels in Oman, which were not found in the blood of European sheep, goats, and cows. Similar blood studies conducted in several countries within the Arabian Peninsula, Egypt, and the Canary Islands of Spain also showed the presence of antibodies in camel blood. This indicates that ungulate mammals were once infected with the virus.

However, the strongest evidence of dromedary involvement came from Qatar in October 2013. There, camel herd owners and their colleagues were diagnosed with MERS.Nasal swab test shown Five of the 14 camels on their farm were MERS positive..In addition, the total viral genome sequences obtained from humans and camels 99.5-99.9% identical..

Scientists believe that camels are intermediate hosts and suspect that bats are the original reservoir of MERS-CoV.This is because some bat species, like the South African particolored bat Harbor virus It is related to what causes MERS.But there is still Evolutionary gap Between those bat viruses and human or camel versions.

“We haven’t found a very close virus yet,” said Chantal Reusken, a virologist at the Dutch Institute of Public Health and Environment in the Netherlands.