To a list of factors besides COVID-19's increased affinity for ACE2 receptors should be added the mutational machinery mentioned in this Chinese report:
The outbreak of COVID-19 has brought great threat to human health. Its causative agent is a severe acute respiratory syndrome-related coronavirus which has been officially named SARS-CoV-2. Here we report the discovery of extremely low CG abundance in its open reading frames. We found that CG...
www.ncbi.nlm.nih.gov
'....We report the discovery of extremely low CG abundance in SARS-CoV-2 open reading frames (ORFs). We found that CG reduction in SARS-Cov-2 is achieved mainly through mutating C/G into A/T and CG is the best target for mutation. Meanwhile, 5'-untranslated region of SARS-CoV-2 has high CG content and is capable of forming an internal ribosome entry site (IRES) to recruit host ribosome for translating its RNA. These features allow SARS-CoV-2 to reproduce efficiently in host cells, because less energy is consumed in disrupting the stem-loops formed by its genomic RNA.
Notably, genomes of cellular orgnisms have very low CG abundance suggesting that mutating C/G into A/T occurs universally in all life forms. Moreover, SRS-CoV-2 has evolved to decrease CG dinucleotide in its open reading frames (ORFs). Moreover, CG is the dinucleotide related to CpG island, mutational hotspot and single nucleotide polymorphism in cellular organisms. After being released into cytoplasm of a host cell, viral RNA is translated immediately to produce viral proteins by using the translational machinery of host cells.
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The stability of the stem-loop structure is dependent on number of hydrogen bonds formed between bases in the stem part. Because C-G and T-A base-pairs are formed through three and two hydrogen bonds, respectively, a viral RNA strand with high numb of C and G bases will form more stable stem-loops than that with high number of T and A bases....We analysed dinucleotide distribution and stability of twenty-four coronavirus species. We found that ORFs of SARS-CoV-2 have an extremely low abundance of CG dinucleotide. The secondary structure of SARS-CoV-2 genomic RNA is less stable than many other coronaviruses. Therefore, it is suggested that SARS-CoV-2 is more efficient in reproduction than other coronaviruses, because less energy is consumed in disrupting the stem-loops formed by its genomic RNA.
In our opinion, it is the lower C/G content in genomic RNA that allows SARS-CoV-2 to reproduce higher numbes of virus particles before triggering the immunoreaction of host cells, because less energy is consumed in replicating each virus particle.'
