Identification, Genetic Analysis, and Pathogenicity of Classical Swine H1N1 and Human-Swine Reassortant H1N1 Influenza Viruses from Pigs in China

Abstract

Swine influenza virus causes a substantial disease burden to swine populations worldwide and poses an imminent threat to the swine industry and humans. Given its importance, we characterized two swine influenza viruses isolated from Shandong, China. The homology and phylogenetic analyses showed that all eight gene segments of A/swine/Shandong/AV1522/2011(H1N1) were closely related to A/Maryland/12/1991(H1N1) circulating in North America. The HA, NA, M, and NS genes of the isolate were also confirmed to have a high homology to A/swine/Hubei/02/2008(H1N1) which appeared in China in 2008, and the virus was clustered into the classical swine lineage. The gene segments of A/swine/Shandong/AV1523/2011(H1N1) were highly homologous to the early human H1N1 and H2N2 influenza viruses, except for the HA gene, and the virus was a reassortant H1N1 virus containing genes from the classical swine (HA) and human (NA, PB2, PB1, PA, NP, M, and NS) lineages. Both the viruses could cause lethal infection and replicate efficiently in the lungs, brains, spleens, and kidneys of mice. Histopathological examinations showed that AV1522 and AV1523 viruses caused a spectrum of marked pneumonia and meningoencephalitis according to the duration of infection, demonstrating a progression of respiratory disease and neurological disease over the course of infection that ultimately resulted in lethality for the infected mice. The changes in the pathogenicity of swine influenza viruses to mammals, accompanied with the continuous reassortment and evolution of the viruses, highlights the importance of ongoing epidemiological investigation.

Special Issue “Emerging Viruses: Surveillance, Prevention, Evolution, and Control”

“…H1N1 swine influenza features are also addressed in this issue. Song et al [10] compare phylogenetic and pathogenic features of two swine influenza H1N1 viruses isolated from Shandong. By phylodynamics analyses, Adam et al [11] suggest an increased selection of influenza H1N1/pdm09 clade 6b residues and other high mortality mutants in India.…”

Influenza A Virus in Pigs in Senegal and Risk Assessment of Avian Influenza Virus (AIV) Emergence and Transmission to Human

“…The FluServer ( , accessed on 14 December 2022) was used to identify key amino acid mutations. The HA cleavage sites of all H1 viruses were characterized as monobasic residue PSIQSR/GLF, while those of the H3 subtype contained the motif PEKQTR/GI at the cleavage site, which is consistent with the characteristics of low pathogenic influenza viruses [ 17 ]. Compared with reference strains A/GuangdongMaonan/SWL1536/2019 (H1N1) and A/Brisbane/02/2018 (H1N1), HA of Senegalese H1 strains had several amino acid substitutions, including V204D, E206Q in 10 isolates and R240Q in 1 isolate.…”

“…They appeared unique in having both α-2,3-linked sialic acid (α-2,3-SA) and α-2,6-linked sialic acid (α-2,6-SA) receptors distributed throughout their respiratory tracts, where avian, swine and human influenza viruses can undergo genetic reassortment (when they infect the same host cell and exchange genetic material), resulting in the creation of novel viruses [ 15 , 16 , 17 ]. Once established in swine, novel reassortant viruses could pose a substantial threat to swine populations and, with introductions and/or reintroductions into humans, could potentially pose outbreak and pandemic risks [ 17 ]. This risk is exemplified by the emergence of the swine-origin A/H1N1pdm09 virus in Mexico and the United States in April 2009 [ 18 , 19 ].…”

Emerging Viruses Besides the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

“…Besides IBV, it is to be noted that the H5N1 highly Pathogenic Avian Influenza (HPAI) virus subtypes from the family Orthomyxoviridae caused several outbreaks in poultry over 60 countries of Asia, Europe, and Africa with 861 confirmed human cases of the avian influenza A(H5N1) virus infection from 16 countries, which denotes the H5N1 HPAI subtype as a significant health threat both to human and poultry [11]. The detailed biology of the influenza viruses, their transmission, epidemiology, pathology, diagnosis, treatment strategies with trial-based vaccines; and the proper prevention and control measures have been well discussed in the range of literature [12][13]. The pandemic potential of H7N9 subtype has been deduced to be of a great global concern; and interestingly, the early H7N9 viruses were noticed to lack the basic hemagglutinin and neuraminidase (HA) cleavage site with a relatively low pathogenicity whereas the subtype analyzed by Wang and colleagues (in 2017) was found to impart high pathogenicity and the replication potential in chickens together with the contact transmission mode [14].…”