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Selective Pressure of SARS-CoV-2 Spillover into Pets

The SARS-CoV-2 pandemic is a complicated and crucial topic in modern day biology. The future development of the pandemic depends on the evolution of new variants. Previous coronaviruses have a strong history of animal reservoirs and zoonotic spillover, and one leading theory on the emergence of SARS-CoV-2 is by zoonotic spillover from bats. In this study, we construct phylogenetic trees and calculate dN/dS ratios for sequences of SARS-CoV-2 in humans, domestic cats, and domestic dogs. We explore the possibilities of SARS-CoV-2 evolution within animal hosts via comparison of phylogenies and quantifying selective pressure of the various hosts. We find that the phylogenies of structural genes compared to non-structural genes were consistent with each other, suggesting minimal intraspecies evolution. Instead, we found the viral strains were clustered by geographical location and date of sample collection, suggesting that  as the virus spilled over it was not under selective pressure. Analysis of dN/dS ratios reveals no significant selective pressure across both structural and non-structural genes. These results suggest that SARS-CoV-2 may not be evolving differently in domestic cats and dogs than in humans, and further studies are necessary to explore other animal species.

Annalise Cramer '23
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