Bats, roadblocks and the origins of coronavirus

The World Health Organization is preparing to visit China next month, after being tasked with investigating the origins of the Covid-19 virus.

In the meantime, the BBC has been to Yunnan province in the south of China where a decade-long project has been taking place to sample the viruses carried by bats.

But, as our China correspondent John Sudworth reports, the Chinese authorities appear to be far less keen on scrutiny.