Transcript for The source of COVID-19: What we know
On December 31 Tony in nineteen. Seafood market and Wuhan China which shut down after officials reported that it was connected to an outbreak of viral pneumonia in the city. Now over a year into the Covert nineteen and I battle is still known about where the virus came. Have to have a really good situational awareness to the put out the embers before you end up with a wildfire. The World Health Organization took a group of seventeen international experts to Wuhan. To work with the Chinese collaborators on an in depth search for cope with nineteen origins members of the group are now sharing details on their findings. At that gathering. We'll lose disparate bits of information. Had their investigation change what we know about the virus. How long can eat for yet definitive answers on how outbreaks are. Chris I understand where this iris came. So that we can't understand how it is not future outbreaks going to oratory. Not about being your -- it's just about understanding. It so that we know how to do better in the future. Since the first discovery of a mystery virus annually between nineteen. Researchers have been trying to pin down exactly work have in nineteen came from. Their search begins with the seafood market in Wuhan China with the shutdown on December 31 after doctors can I get as a link between number of mystery cases of pneumonia and city. As researchers try to juggle contact tracing environmental testing and the challenges of an outbreak. The virus speaking to spread across the globe. On January 13 the first known case of coveted eighteen was reported outside China. Two more countries report their first series in the next few days and more would follow. Many initial cases where people who recently traveled from China this outbreak grew local transmission became more common. I marks 100 countries and territories reported at least one case of corporate 200 countries and territories reported at least one case April. By early tween tween run. Or 100 million cases were reported across more than 200 in twenty countries and territories. The look back on exactly what have been in China ballot and not very clear. Huge show. I hear people in pairs figure out what she's on rock. The teel time to do an outbreak investigation. Is wrong that Tanya right stuff but I think we've got to remember that. This wasn't incredibly difficult period for the victim who hung didn't mean tens of thousands of kinds. Earlier academic researchers say that they determined that the virus likely hats in the attic margins immediately to jump from animals to people. Not a disease outbreak is happy to wait you have humans in contact with an animal. It's an infected. With the virus could be. Canceling an. Eating meat and could be carrying that animal for our market and do not outbreaks happen anywhere. That are more in depth investigation would be needed to understand how the virus made its way into the human population. Investigations like this can take years to complete. Her best analogy that is. Almost. 2003. SARS lines. Stars align merged at best as weak and help old. Running back team in China then went to an intermediary animal and man T he'll. Took several years an investigation. After that r.s one out great eating get to that. A year after the first cases were reported. The Debbi HL appointee to keep a virologist. Epidemiologist. And the largest to investigate the origin of the pirates will hunt. A report detailing their findings offer some leads about where a virus may have come from but it's also been plagued with Khartoum. RC there have been allegations. That Chinese authorities were not tired weak or funny how certain rocky it was Al. Or the last war the best and most thorough investigation. And a and here's in the early months. And where we can go. The team visited several locations in Wuhan that could offer clues about the origin of cup in nineteen. One of the locations with Quan on seafood market. Market and move on which was associated with the first known cluster of cases. What markets like this all meat fruits and vegetables and artists such a low class resource for their surrounding communities. Some markets also installs itself armed wild camels. Early environmental testing in the market countries is the virus on some surfaces. Investigators determined three likely Pakistani merchants for how the virus could make its way into the market and other market place. That three Erie that they had narrowed this down tube. All have to do way back ask our calls are. Even. Researchers feel pretty confident about that because of what they know about the way east corona viruses circulate in populations and because of prior experience with corona virus coming from. Theory number Warren. Add it to an intermediary. Which then gives it to her purse although they don't know for sure what Erie animal it. Theory number two that either directly to her. This could happen because I'm out there hunting logging market in each here with that area. The third possibility is that it started fast but then somehow got into an animal that rose in for food. And then transported longer distance. And that means that the act Meehan or that intermediary reservoir. Could potentially he farther away. The World Health Organization says that researchers in China have tested 50000 samples from 300 different species but none have been positive for XR Scobey to. Tested while. Life that was coming from while croissants and in the market and it looks like those animals some of those animals work of the time that should carry corona virus is not a smoking jungle it's a clue. This morning and something that was don't we don't act the outbreak in the war room in the nose wheels that is where we operate and those who send. Despite early this cluster of cases having an association with the market a large portion of cases appeared to have no connection at all. In order to better understand where else the virus was circulating. Another location they visited it was who they provincial hospital and integrate cheneys and western medicine for some of the first case of Covert were treated. Here and several other hospitals it is it in the area they look to early sequencing data from the virus. Our state dancing Israeli type the genetic material in the Abbas and determinant structure it's like contact tracing that using molecular biology. Like most fire says SARS closely to mutates over time. And it's genetic makeup can change as it's passed between people. If two people have a strain of the virus to have the scene sequence image that they likely caught the virus from a common source. If they're sequences are different in is that they're likely caught the virus from different place as they may have a common source further back in history that viruses life. But it's genetic sequence has changed as it's been passed to give her people. The more different sequences there are more likely it is that the virus had more time to circulate and has passed through more places. If anything in Wuhan in December was exactly the same state that's been in constant thing they call cancels the spinoffs. Always had a thing Wuhan in December was already. The spirit of a couple of different mind variants of the box. And that again suggests there may be divisive things that can I think a little bit longer than they would realize. The team also said that the multiple early sequences found likely means that one on seafood market was not the primary source. We nodded in the first. 170 cases in this and a little of them had exposure to them not. The mother was sitting in and thought that probably not the actual source of the whole right again this. One of the final locations and visited with the Wuhan institute of hydrology. This lab and several others in the CE with a target of a politically charged theory that the pirates have accidentally leaked from a lap. Researchers have stated that prior genomic sequencing showed that the virus had natural origin it's. The ideas on terrorism bank. It was not. Visiting each ER is something toxic and perhaps as scientists went out and you'll collect it is in. Riot act laboratory. Was accident and introduced. Egypt and China. Let leaks do look at it and fortunately it rid. We did discuss with them did lot of security measures in song. What we're doing around stuff pill and had they gone back and check this out they didn't find anything. While these laughs we're studying viruses. In some backward ones. The teen says that they found it highly unlikely that the virus had leaked from any of these facility east. The most closely related debt for our school all right TG citizen. Is and you actually genetic sequences and a law bars. High altitude policy alliance in the cheek and had the latest from something like that. Not ruled anything out we cannot rule anything sense count rule things out like that although it did find is that the lab to skate was extremely unlikely. In their report the team concluded that most likely pathway transmission was from back to an intermediary animal. We noted that there is a whole range of corona viruses and that a number of these abortive move to cross into humans such as sounds. A range of viruses. That are related to south Kennedy 2 or evening found the net is still not close enough today's apparent. Boss in July this is suggestion and very closely related viruses and. However the team says that they if not fully ruled out any here case. This for more actively laying ground work for future science research and her eight years and months content. They're giving us and that got us focus our T in this particular direction. Is most likely. So police to happen now is the next steps tracing back the first cases. What the markets to negotiate happens traced back to the supporters of the market and see if they have a mutual spikes of antibodies I don't is that we know. Susceptible and we should look at whether we have concentrations. If this can't get it hasn't hide anything it should have driven this point it in action anywhere is actually an infection every hair. So we need to really think disease surveillance. As population increases. Encroached. Upon in areas where wild animals. As we continue to have printed teens we will see more viruses just being friendly animals to humans. And we're going to see more disease emergency facts.
This transcript has been automatically generated and may not be 100% accurate.