Scientists traveled into the forests of northern Laos in the summer of 2020, half a year into the coronavirus pandemic, to catch bats that might harbor close cousins of the pathogen.

They used mist nets and canvas traps to capture the animals as they emerged from nearby caves at night, collected saliva, urine, and feces samples, and then released them back into the darkness.

The fecal samples were found to contain coronaviruses, which the scientists studied in BSL-3 biosafety labs using specialized protective gear and air filters. Virus researchers are ecstatic about the discovery. Some believe that SARS-CoV-2-like viruses are already infecting people on a regular basis, causing only mild and limited outbreaks. However, they believe that under the right conditions, the pathogens could cause a Covid-19-like pandemic.

According to experts, the findings have significant implications for the contentious debate over Covid’s origins. Some have speculated that SARS-remarkable CoV-2’s ability to infect human cells could not have evolved naturally from an animal. The new findings, however, appear to suggest otherwise.

These bat viruses, along with more than a dozen others discovered in recent months in Laos, Cambodia, China, and Thailand, may also aid researchers in forecasting future pandemics. The viruses’ family trees provide clues as to where potentially dangerous strains might be hiding and which animal scientists should look for them in.

The US government announced a $125 million project last week to identify thousands of wild viruses in Asia, Latin America, and Africa and assess their risk of spillover. Dr. Eloit predicted that there would be many more SARS-CoV-2 relatives to discover.

When SARS-CoV-2 was discovered, its closest known relative was a bat coronavirus discovered in a mine in southern China’s Yunnan Province in 2016. RaTG13, as it is known, has 96 percent of its genome in common with SARS-CoV-2. Scientists believe RaTG13 and SARS-CoV-2 share a common ancestor that infected bats about 40 years ago based on the mutations carried by each virus.

Both viruses infect cells by attaching to their surface with a molecular hook known as the “receptor-binding domain.” RaTG13’s hook, which was designed to attach to bat cells, can only cling to human cells weakly. The hook of SARS-CoV-2, on the other hand, can clasp cells in the human airway, the first step toward a potentially lethal case of Covid-19.

Wildlife virus experts searched their freezers full of old samples from around the world for other close relatives of SARS-CoV-2. They discovered several coronaviruses with similar characteristics in southern China, Cambodia, and Thailand. The majority came from bats, with a few from pangolins, which are scaly mammals. RaTG13 was the closest relative.

They went to northern Laos, about 150 miles from the mine where Chinese researchers discovered RaTG13. They caught 645 bats from 45 different species over the course of six months. Two dozen coronaviruses were found in the bats, three of which were strikingly similar to SARS-CoV-2, particularly in the receptor-binding domain.

11 of the 17 domain key building blocks in RaTG13 are identical to those in SARS-CoV-2. However, as many as 16 viruses from Laos were identical — the closest match to date.

Dr. Eloit hypothesized that one or more of the coronaviruses could infect humans and cause mild disease. In a separate study, he and colleagues collected blood samples from people who collect bat guano for a living in Laos. Although the Laotians showed no signs of having been infected with SARS-CoV-2, they did carry immune markers known as antibodies that appeared to be caused by a similar virus.

The renewed interest in the pandemic’s origins has focused attention on the precautions that researchers take when studying potentially dangerous viruses. According to a USAID spokesman, scientists will be required to provide a biosafety and biosecurity plan, which will include staff training, guidelines on protective equipment to be worn in the field, and safety measures for lab work, in order to receive DEEP VZN grants.

If scientists discover more SARS-CoV-2 close relatives, it does not necessarily imply that they pose a deadly threat. They may not spread to humans or, as some scientists speculate, may cause only minor outbreaks. There are only seven coronaviruses known to have crossed the species barrier and become well-established human pathogens.