Tracing the Zoonotic Origins of a Rare Human G5P[6] Rotavirus in Brazil

The porcine origin rotavirus A (RVA) G5 genotype is notable for its unique and sustained human circulation in Brazil, primarily as G5P[8] during the 1980s-2000s. This study aimed to characterize and investigate the full genome of a rare G5P[6] strain detected in 2013 (RVA/Human-wt/BRA/IAL-R406/2013/G5P[6]) to elucidate its evolutionary origin throughout RT-PCR, sequencing, and phylogenetic analysis. Whole-genome assessment revealed an atypical G5-P[6]-I1-R1-C1-M1-A8-N1-T7-E1-H1 constellation. The IAL-R406 VP7 (classified in Lineage I) was closely related to G5 strains that have circulated in both humans and pigs in Brazil for nearly three decades, showing no evidence of recent variant introduction. The VP4 P[6] (assigned as Lineage I) was genetically similar to Paraguayan and Argentinian G4P[6] porcine-like strains, indicating a regional swine reservoir and zoonotic RVA spillover in South America. The remaining nine segments support the animal-human reassortant origin of IAL-R406, showing broad similarity to porcine-like human and porcine strains described worldwide, with additional relationships to bovine (Republic of Korea, USA), feline-like human (Brazil), equine (UK), simian (Caribbean), wild boar/fox (Croatia), and classical human (Japan, USA) strains. In particular, the NSP1-A8 and NSP3-T7 genotypes, extremely rare in humans yet widespread in animals, especially swine, strongly indicate interspecies reassortment, likely resulting from porcine-to-human transmission. Together, these findings reinforce swine as a persistent reservoir for zoonotic RVA infections and highlight the importance of a One Health approach integrating human and animal surveillance to better understand RVA cross-species transmission and evolution.