A gene which helps the spread of SARS-CoV-2, the virus that causes COVID-19, in humans "appears to reduce the infectivity of a similar bat virus," the South China Morning Post has reported, citing a new U.S. government study.

According to the report, Dr Tony Wang and colleagues at the U.S. Food and Drug Administration's vector-borne viral diseases laboratory in Maryland gave raTG13, the closest known relative to SARS-CoV-2, a spike similar to that of Sars-CoV-2. Spikes are proteins that bind the virus to a host cell.

"The most striking finding of this study is that insertion of PRRA into the raTG13 spike protein altered the ability of relevant pseudovirus to utilize ACE2 of three species to gain entry," the researchers said in their paper published as a pre-print on the website BioRxiv.

"Structural and biochemical studies have suggested that SARS-CoV-2 may have been well adapted in human before the outbreak in Wuhan, China," they added in the paper.

The new study "may cast doubt on a theory that the virus originated in a Chinese laboratory," the South China Morning Post reported.