https://www.dailymail.co.uk/health/article-12969105/chinese-scientists-lab-coronavirus-kill-rate-mice.html
According to the study, carried out by the Beijing University of Chemical Technology, the virus was discovered in 2017 prior to the Covid outbreak.
It was discovered in Malaysia in pangolins - scaly mammals that are known harborers of coronaviruses and were heavily speculated to be the intermediate host that passed Covid from bats to humans.
The researchers cloned the virus and stored multiple copes in the Beijing lab, where it continued to evolve.
It is unclear when the newly surfaced study was conducted. But the researchers said it was possible the virus had undergone a 'virulence-enhancing mutation' in storage, which made it more deadly.
For the new research, eight mice were infected with the virus, eight were infected with an inactivated virus and eight were used as a control group.
All mice infected with the virus died. They succumbed to the infection between seven and eight days after being infected.
Symptoms included their eyes turning completely white, rapid weight loss and fatigue.
Researchers found 'significant amounts' of the virus in the rodents' brains, lungs, noses, eyes and windpipes.