If we want to prevent viral infections or develop drugs that can effectively treat them, those infections have to be investigated and understood. As such, scientists have long been researching viruses found in animals that have the potential to infect humans. Many spillover events, in which a virus has jumped from one host species to another, have led to illness epidemics and pandemics. Scientists have now found that a group of viruses found in bats, which are close relatives of the Middle East respiratory syndrome coronavirus (MERS-CoV), may be only one mutation from gaining the ability to infect human cells. The researchers are warning that these viruses have the potential to cause the next pandemic. The work has been reported in Nature Communications.
This study focused on a group of coronaviruses called merbecoviruses, which includes MERS-CoV, to determine how they infect host cells. Although the majority of merbecoviruses currently pose no direct threat to humans, one subgroup called HKU5 is a concern.
"Merbecoviruses, and HKU5 viruses in particular, really hadn't been looked at much, but our study shows how these viruses infect cells," noted Michael Letko, a virologist at Washington State University. "What we also found is HKU5 viruses may be only a small step away from being able to spillover into humans."
HKU5 merbecoviruses have been found across Africa, Asia, Europe, and the Middle East. They seem to use a viral spike protein to bind to host cells, and they utilize ACE2 to infect those cells (like SARS-CoV-2, which causes COVID-19) However, HKU5 viruses are still only able to bind to a bat ACE2 receptor, and do not bind well to the human version of ACE2. (In Asia, the natural host of HKU5 is the Japanese house bat.)
But genetic mutations that change the HKU5 spike protein could enable it to bind to ACE2 proteins carried by other species, including humans.
A Chinese HKU5 virus has already crossed into minks, so this virus has the potential to make these changes.
"These viruses are so closely related to MERS, so we have to be concerned if they ever infect humans," Letko said. "While there's no evidence they've crossed into people yet, the potential is there, and that makes them worth watching."
MERS is a respiratory illness that can be transmitted to humans from dromedary camels. It has a mortality rate over 30%.
Now, these findings could potentially be used in the design of new vaccines or treatments, noted Leko. However, this project was funded by the National Institutes of Health, and continued efforts on those fronts will require sustained, stable funding.