Appearance of reassortant European avian-origin H1 influenza A viruses of swine in Vietnam

Abstract

Three subtypes-H1N1, H1N2 and H3N2-of influenza A viruses of swine (IAVs-S) are currently endemic in swine worldwide, but there is considerable genotypic diversity among each subtype and limited geographical distribution. Through IAVs-S monitoring in Vietnam, two H1N2 influenza A viruses were isolated from healthy pigs in Ba Ria-Vung Tau Province, Southern Vietnam, on 2 December 2016. BLAST and phylogenetic analyses revealed that their HA and NA genes were derived from those of European avian-like H1N2 IAVs-S that contained avian-origin H1 and human-like N2 genes, and were particularly closely related to those of IAVs-S circulating in the Netherlands, Germany or Denmark. In addition, the internal genes of these Vietnamese isolates were derived from human A(H1N1)pdm09 viruses, suggesting that the Vietnamese H1N2 IAVs-S are reassortants between European H1N2 IAVs-S and human A(H1N1)pdm09v. The appearance of European avian-like H1N2 IAVs-S in Vietnam marks their first transmission outside Europe. Our results and statistical analyses of the number of live pigs imported into Vietnam suggest that the European avian-like H1N2 IAVs-S may have been introduced into Vietnam with their hosts through international trade. These findings highlight the importance of quarantining imported pigs to impede the introduction of new IAVs-S.

Long-term epidemiology and evolution of swine influenza viruses in Vietnam

“…Through continuous surveillance at a central slaughterhouse in Hanoi, which sourced pigs from across the country, we found that only H1N1, H1N2 and H3N2 were present and co-circulating. This is consistent with previous surveillance at the same slaughterhouse in 2013/14 (13,14) and other studies in Vietnam (15,16,17),…”

“…(a) Numbers of swine Influenza viruses isolated from Van Phuc slaughterhouse during 2013–2014 (13, 14) and 2016–2019 (denoted in red), alongside other surveillance studies in Vietnam shown in green (15, 16, 17). (b) Prevalence of swine influenza virus subtypes.…”

“…Additionally, two viruses of the H1N2 subtype collected in December 2016 by Takemae et al . (2018) (17) belong to the Eurasian avian (EA)-like swine H1 HA lineage. The H3-HA phylogeny indicates SwIV in Vietnam belong to either the swine-origin North American TR lineage or the 2003/04 human H3N2-origin SwIV first detected in Vietnam in 2010 ( Fig 2b , Fig S1).…”

The epidemiology of swine influenza

“…H1N1, H1N2 and H3N2 subtypes are cocirculating in pig population in Vietnam, and spill-over infection of human origin influenza viruses to pigs were detected. Notably, some SIV reassortants had infected humans (Takemae et al 2017 ; Baudon et al 2018 ; Takemae et al 2018 ; Baudon et al 2020 ). Similarly, the three subtypes are also prevalent in the pig population of Thailand and A(H1N1)pdm09 and its reassortants are found as the predominate strains in the field (Nonthabenjawan et al 2015 ; Mine et al 2019 ; Nasamran et al 2020 ).…”

Genetic Characterization of Influenza A Viruses in Japanese Swine in 2015 to 2019

“…Classical swine H1N1 IAVs-S were first isolated in North America in 1930 and have been infecting pigs endemically there since the 1970s, currently circulating among pig population worldwide, whereas avian-like H1N1 IAVs-S have stably persisted in Europe since 1979 ( 7 , 8 ). In Asia, avian-like H1N1 IAVs-S was first isolated in China in 1993 ( 7 , 9 , 10 ), and reassortant IAVs-S containing genes derived from avian-like H1N1 IAVs-S have been reported in Thailand ( 11 – 14 ), South Korea ( 15 ), and Vietnam ( 16 ). A/Hong Kong/1968-like H3N2 viruses have been isolated from pigs in Asia and Europe, indicating the worldwide circulation of human-like H3N2 IAVs-S, while some cases of the isolation of avian-like H3N2 IAVs-S were reported in Asia in the 1970s ( 17 – 21 ).…”