When a new zoonotic outbreak occurs, scientists rush to trace the species the infection originated from. Often the infection jumps from its initial animal carrier to an intermediate host species, which then transmits the virus to humans. Identifying intermediate host species enable risk-mitigating public health policies to be implemented and gives researchers a better understanding of the disease evolution and pathogenesis.
The going hypothesis is that the current outbreak started in bats, then moved to another species. While many of the earliest cases in Wuhan were linked to the Huanan Seafood market—which sold seafood and wildlife, including snakes and birds—not every case has a link to it. The wide variety of animal produce available at the market, and structural similarities of ACE2 receptors in many “suspect species” means scientists are still not confident about the transmission chain of SARS-CoV-2.
The authors propose—based on structural similarities between the viral RBD and host ACE2—that pangolins, snakes, and turtles could be possible intermediate hosts of SARS-CoV-2.
The authors note that further research is needed to confirm these findings, while other experts have discredited the idea put forth by a different group of researchers in January that snakes are SARS-CoV-2 hosts.