As genomic nucleotide composition is strongly associated with codon usage bias in viruses, we examined the codon usage in the genomes of the novel bat SaV and other SaVs given their different nucleotide composition. The bat SaV genome was found to have significantly greater codon usage bias than the other SaV genomes, as measured by their effective number of codons (N c ) ( Figure 4 ). Adjusting N c for background nucleotide composition (N c 9) did not significantly affect the observed difference in codon usage bias.