Nature Horseshoe bats carry viruses closely related to SARS-CoV-2, but they probably can’t spread in people yet.
Coronavirus hunters looking for the next pandemic threats have focused on China and southeast Asia, where wild bats carry SARS-CoV-2’s closest known relatives.
But a survey of UK bat species suggests that researchers might want to cast a wider net. The trawl turned up new coronaviruses, and some from the same group as SARS-CoV-2.
Laboratory studies with safe versions of these viruses suggest that some share key adaptations with SARS-CoV-2 — but are unlikely to spread in humans without further evolution.
SARS-CoV-2 belongs to a group of coronaviruses called sarbecoviruses, which circulate in bats. But before the pandemic, efforts to find and characterize these viruses focused on Asia. “Europe and the UK had been totally overlooked,” says Vincent Savolainen, an evolutionary geneticist at Imperial College London who led the study, published on 27 June in Nature Communications1.
To help plug this gap, Savolainen and his colleagues teamed up with groups involved in bat rehabilitation and conservation to collect a total of 48 faecal samples from bats representing 16 of the 17 species that breed in the United Kingdom. Genetic sequencing turned up nine coronaviruses, including four sarbecoviruses and one related to the coronavirus responsible for Middle East Respiratory Syndrome, or MERS, which periodically spills over into camels and humans.
Ties that bind — or not
To gauge the threat posed by the UK coronaviruses, the researchers created pseudoviruses: non-replicating forms of HIV that are engineered to carry the spike protein that coronaviruses use to infect cells. One sarbecovirus found in a lesser horseshoe bat (Rhinolophus hipposideros) had a spike protein that was able to infect human cells by attaching to a protein called ACE2, the same receptor used by SARS-CoV-2.
But the UK sarbecovirus’s version of spike didn’t attach nearly as strongly as SARS-CoV-2’s, and pseudoviruses could infect only human cells with unnaturally high levels of ACE2. This makes it unlikely that the virus could readily infect people and spread, the researchers say.
That’s reassuring, but other sarbecoviruses circulating in British bats could be able to bind to human ACE2 more efficiently, says Michael Letko, a molecular virologist at Washington State University in Pullman, who was not involved in the study. A February preprint2 surveyed UK lesser horseshoe bats and found signs that around half were infected with sarbecoviruses. Further adaptations that help these viruses to infect human cells more efficiently might not be hard to come by, Letko says. “Once the virus has its foot in the door, it’s easier to adapt further.”
Tyler Starr, a molecular evolutionary biologist at the University of Utah in Salt Lake City, says that sarbecoviruses identified so far in Europe and in Africa probably represent the tip of the iceberg when it comes to the group’s true diversity and geographical distribution. He wouldn’t be surprised if the next sarbecovirus to spill over into humans came from an unprecedented location or branch of the family tree. “The next pandemic threat could very well be in our own backyard,” adds Letko.