Abstract
Swine are an important intermediate host for emergence of pandemic influenza. Vietnam is the largest swine producer in South East Asia. Systematic virological and serological surveillance of swine influenza viruses was carried out in Northern Vietnam from May 2013 to June 2014 with monthly sampling of pigs in local and large collective slaughterhouses and in a live pig market. Influenza A seroprevalence in the local slaughterhouses and in the large collective slaughterhouse was 48.7% and 29.1%, respectively. Seventy-seven influenza A viruses were isolated, all from the large collective slaughterhouse. Genetic analysis revealed six virus genotypes including H1N1 2009 pandemic (H1N1pdm09) viruses, H1N2 with H1 of human origin, H3N2 and H1N1pdm09 reassortants, and triple-reassortant H3N2 viruses. Phylogenetic analysis of swine and human H1N1pdm09 viruses showed evidence of repeated spill-over from humans to swine rather than the establishment of H1N1pdm09 as long-term distinct lineage in swine. Surveillance at the large collective slaughterhouse proved to be the most efficient, cost-effective, and sustainable method of surveillance for swine influenza viruses in Vietnam.
Highlights
Introduction The2009 H1N1 influenza A pandemic virus (H1N1pdm09) emerged in Mexico as a reassortant virus originating in swine[1,2]
88% of the pigs originated from the Red River Delta (RRD) (40% from Hanoi, 18% from Ha Nam), 8% from Northern provinces and 4% from Central provinces
A total of 77 swine influenza viruses (SIV) of H1N1, H1N2, and H3N2 subtypes were isolated in the collective slaughterhouse, an isolation rate similar to that reported from surveillance in farms in Southern and Northern Vietnam[28] and other studies across Asia[37]
Summary
2009 H1N1 influenza A pandemic virus (H1N1pdm09) emerged in Mexico as a reassortant virus originating in swine[1,2] This re-enforced the concept that swine are a “mixing vessel” for avian and human viruses and an intermediate host for pandemic emergence and highlighted the importance of influenza surveillance in swine[3,4]. H9N2, H5N1, and H7N9 are frequently detected influenza subtypes in Baudon et al Emerging Microbes & Infections (2018)7:123 poultry, often raised in close proximity to swine, raising concerns of generating novel reassortants with endemic swine viruses because of the potential role of swine as a “mixing vessel” for the avian and human influenza virus gene pools[14,15]. Disease surveillance systems are often costly and there is a need to develop cost-effective and sustainable surveillance especially in resource scarce countries[23,24]
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