The exact evolutionary patterns of human G4P rotavirus strains remain to be elucidated. Such strains possess unique and strain-specific genotype constellations, raising the question of whether G4P strains are primarily transmitted via independent interspecies transmission or human-to-human transmission after interspecies transmission. Two G4P rotavirus strains were identified in fecal specimens from hospitalized patients with severe diarrhea in Thailand, namely, DU2014-259 (RVA/Human-wt/THA/DU2014-259/2014/G4P) and PK2015-1-0001 (RVA/Human-wt/THA/PK2015-1-0001/2015/G4P). Here, we analyzed the full genomes of the two human G4P strains, which provided the opportunity to study and confirm their evolutionary origin. On whole genome analysis, both strains exhibited a unique Wa-like genotype constellation of G4-P-I1-R1-C1-M1-A8-N1-T1-E1-H1. The NSP1 genotype A8 is commonly found in porcine rotavirus strains. Furthermore, on phylogenetic analysis, each of the 11 genes of strains DU2014-259 and PK2015-1-0001 appeared to be of porcine origin. On the other hand, the two study strains consistently formed distinct clusters for nine of the 11 gene segments (VP4, VP6, VP1-VP3, and NSP2-NSP5), strongly indicating the occurrence of independent porcine-to-human interspecies transmission events. Our observations provide important insights into the origin of zoonotic G4P strains, and into the dynamic interaction between porcine and human rotavirus strains.
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