  Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus caused the
novel coronavirus disease-2019 (COVID-19) affecting the whole world. Like
SARS-CoV and MERS-CoV, SARS-CoV-2 are thought to originate in bats and then
spread to humans through intermediate hosts. Identifying intermediate host
species is critical to understanding the evolution and transmission mechanisms
of COVID-19. However, determining which animals are intermediate hosts remains
a key challenge. Virus host-genome similarity (HGS) is an important factor that
reflects the adaptability of virus to host. SARS-CoV-2 may retain beneficial
mutations to increase HGS and evade the host immune system. This study
investigated the HGSs between 399 SARS-CoV-2 strains and 10 hosts of different
species, including bat, mouse, cat, swine, snake, dog, pangolin, chicken, human
and monkey. The results showed that the HGS between SARS-CoV-2 and bat was the
highest, followed by mouse and cat. Human and monkey had the lowest HGS values.
In terms of genetic similarity, mouse and monkey are halfway between bat and
human. Moreover, given that COVID-19 outbreaks tend to be associated with live
poultry and seafood markets, mouse and cat are more likely sources of infection
in these places. However, more experimental data are needed to confirm whether
mouse and cat are true intermediate hosts. These findings suggest that animals
closely related to human life, especially those with high HGS, need to be
closely monitored.
