Genomic epidemiology of human parvovirus B19 in Southern Brazil, 2015–2024

BACKGROUND: Human parvovirus B19 (B19V) causes erythema infectiosum and, in severe cases, has been associated with hydrops fetalis and transient aplastic crises. Despite its clinical importance, particularly in vulnerable groups such as pregnant women and immunocompromised individuals, epidemiological and genomic data on B19V remain limited. METHODS AND RESULTS: We investigated 4,118 samples collected from patients with exanthematous illness in Rio Grande do Sul, Southern Brazil, between 2015 and 2024 using serological and molecular testing, and developed an amplicon-based whole-genome sequencing protocol for B19V, generating 47 near-complete genomes. B19V was detected across all age groups, with a higher frequency among females (62.4%), and among adults aged 21-40 years. Viral circulation was detected year-round, with a modest increase in July and a more pronounced peak in September, consistent with Southern Hemisphere winter seasonality. Forty-one genomes from the 46 included in the dated phylogeny clustered in a single well-supported clade containing sequences from other Brazilian states, with Rio Grande do Sul sequences interspersed rather than forming a single lineage derived from one introduction. The remaining five genomes clustered with sequences from other regions of Brazil and Argentina. This phylogenetic pattern reflects sustained endemic circulation through repeated local transmission and is not adequately captured by current genotype-level classification systems. CONCLUSIONS: The findings of this study expand the genomic understanding of B19V in South America and provide important insights into its molecular epidemiology, seasonal patterns, and evolutionary history in Southern Brazil.