The pair-wise receptor sequence similarities ( g S i,1 , g S i,2 , and g S i,3 ) between host-species pairs for each virus family are shown in Table 1 . For logical comparisons, each virus contains at least one infected host (the primary reservoir, designated as "#" in Table 1 ). As shown in Table 1 , the similarity scores for the infected group (g = 1) were high, ranging from 0.790 to 0.988 for 1 S i,1 , from 0.841 to 0.996 for 1 S i,2 , and 0.794 to 0.962 for 1 S i,3 . All pair-wise comparisons in group 1 (human vs. primary reservoir, primary reservoir vs. host, and human vs. host) yielded high similarity scores, indicating a high similarity among receptor sequences. The similarity scores were comparatively low in the non-infection group (g = 2), ranging from 0.092 to 0.440 for 2 S i,1 , from 0.108 to 0.432 for 2 S i,2 , and from 0.130 to 0.416 for 2 S i,3 . For group 2, both the primary host species and non-infected species are listed to illustrate the differences in similarity. In pair-wise comparisons, all the non-infection cases yielded low similarity values, i.e., the receptor sequences differed significantly from each other.