Human-to-swine introductions and onward transmission of 2009 H1N1 pandemic influenza viruses in Brazil

Dennis Maletich Junqueira; Caroline Tochetto; Tavis K Anderson; Danielle Gava; Vanessa Haach; Maurício E Cantão; Amy L Vincent Baker; Rejane Schaefer

doi:10.3389/fmicb.2023.1243567

Human-to-swine introductions and onward transmission of 2009 H1N1 pandemic influenza viruses in Brazil

Front Microbiol. 2023 Aug 8:14:1243567. doi: 10.3389/fmicb.2023.1243567. eCollection 2023.

Authors

Dennis Maletich Junqueira¹, Caroline Tochetto², Tavis K Anderson³, Danielle Gava², Vanessa Haach⁴, Maurício E Cantão², Amy L Vincent Baker³, Rejane Schaefer²

Affiliations

¹ Laboratório de Bioinformática e Evolução de Vírus, Departamento de Bioquímica e Biologia Molecular, Centro de Ciências Naturais e Exatas (CCNE), Universidade Federal de Santa Maria (UFSM), Santa Maria, Brazil.
² Embrapa Suínos e Aves, Concórdia, Brazil.
³ Virus and Prion Research Unit, United States Department of Agriculture, National Animal Disease Center, Agricultural Research Service, Ames, IA, United States.
⁴ Laboratório de Virologia, Departamento de Microbiologia, Imunologia e Parasitologia, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil.

Abstract

Introduction: Once established in the human population, the 2009 H1N1 pandemic virus (H1N1pdm09) was repeatedly introduced into swine populations globally with subsequent onward transmission among pigs.

Methods: To identify and characterize human-to-swine H1N1pdm09 introductions in Brazil, we conducted a large-scale phylogenetic analysis of 4,141 H1pdm09 hemagglutinin (HA) and 3,227 N1pdm09 neuraminidase (NA) gene sequences isolated globally from humans and swine between 2009 and 2022.

Results: Phylodynamic analysis revealed that during the period between 2009 and 2011, there was a rapid transmission of the H1N1pdm09 virus from humans to swine in Brazil. Multiple introductions of the virus were observed, but most of them resulted in self-limited infections in swine, with limited onward transmission. Only a few sustained transmission clusters were identified during this period. After 2012, there was a reduction in the number of human-to-swine H1N1pdm09 transmissions in Brazil.

Discussion: The virus underwent continuous antigenic drift, and a balance was established between swine-to-swine transmission and extinction, with minimal sustained onward transmission from humans to swine. These results emphasize the dynamic interplay between human-to-swine transmission, antigenic drift, and the establishment of swine-to-swine transmission in shaping the evolution and persistence of H1N1pdm09 in swine populations.

Keywords: 2009 H1N1; Brazil; influenza A virus; spillover; swine.