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Pathogenesis of swine influenza virus (Thai isolates) in weanling pigs: an experimental trial
Donruethai Sreta, Roongtham Kedkovid, Sophon Tuamsang, Pravina Kitikoon, Roongroje Thanawongnuwech
Virology Journal , 2009, DOI: 10.1186/1743-422x-6-34
Abstract: The study found that all pigs in the infected groups developed typical signs of flu-like symptoms on 1–4 days post- infection (dpi). The H1N1-infected pigs had greater lung lesion scores than those of the H3N2-infected pigs. Histopathological lesions related to swine influenza-induced lesions consisting of epithelial cells damage, airway plugging and peribronchial and perivascular mononuclear cell infiltration were present in both infected groups. Immunofluorescence and immunohistochemistry using nucleoprotein specific monoclonal antibodies revealed positive staining cells in lung sections of both infected groups at 2 and 4 dpi. Virus shedding was detected at 2 dpi from both infected groups as demonstrated by RT-PCR and virus isolation.The results demonstrated that both SIV subtypes were able to induce flu-like symptoms and lung lesions in weanling pigs. However the severity of the diseases with regards to lung lesions both gross and microscopic lesions was greater in the H1N1-infected pigs. Based on phylogenetic analysis, haemagglutinin gene of subtype H1N1 from Thailand clustered with the classical H1 SIV sequences and neuraminidase gene clustered with virus of avian origin, whereas, both genes of H3N2 subtype clustered with H3N2 human-like SIV from the 1970s.Swine influenza is an acute, highly contagious, respiratory disease caused by type A influenza virus infection. Currently, 16 haemagglutinin (HA) subtypes and 9 neuraminidase (NA) subtypes are identified. Three main subtypes currently circulating in the pig population are classical swine influenza virus (SIV) and reassortant viruses of H1N1, H3N2 and H1N2 [1]. However, pigs can also be infected with other subtypes of influenza A viruses. Pig plays a substantially important role in the ecology of influenza A virus [2] since they can act as a 'mixing vessel'. When co-infections among human, avian or swine influenza viruses occur within a specific host, any new subtype can be produced by antigenic reassortment [
Reassortment Patterns in Swine Influenza Viruses  [PDF]
Hossein Khiabanian, Vladimir Trifonov, Raul Rabadan
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0007366
Abstract: Three human influenza pandemics occurred in the twentieth century, in 1918, 1957, and 1968. Influenza pandemic strains are the results of emerging viruses from non-human reservoirs to which humans have little or no immunity. At least two of these pandemic strains, in 1957 and in 1968, were the results of reassortments between human and avian viruses. Also, many cases of swine influenza viruses have reportedly infected humans, in particular, the recent H1N1 influenza virus of swine origin, isolated in Mexico and the United States. Pigs are documented to allow productive replication of human, avian, and swine influenza viruses. Thus it has been conjectured that pigs are the “mixing vessel” that create the avian-human reassortant strains, causing the human pandemics. Hence, studying the process and patterns of viral reassortment, especially in pigs, is a key to better understanding of human influenza pandemics. In the last few years, databases containing sequences of influenza A viruses, including swine viruses, collected since 1918 from diverse geographical locations, have been developed and made publicly available. In this paper, we study an ensemble of swine influenza viruses to analyze the reassortment phenomena through several statistical techniques. The reassortment patterns in swine viruses prove to be similar to the previous results found in human viruses, both in vitro and in vivo, that the surface glycoprotein coding segments reassort most often. Moreover, we find that one of the polymerase segments (PB1), reassorted in the strains responsible for the last two human pandemics, also reassorts frequently.
Pandemic Influenza A Viruses Escape from Restriction by Human MxA through Adaptive Mutations in the Nucleoprotein  [PDF]
Benjamin M?nz equal contributor,Dominik Dornfeld equal contributor,Veronika G?tz,Roland Zell,Petra Zimmermann,Otto Haller,Georg Kochs ,Martin Schwemmle
PLOS Pathogens , 2013, DOI: 10.1371/journal.ppat.1003279
Abstract: The interferon-induced dynamin-like MxA GTPase restricts the replication of influenza A viruses. We identified adaptive mutations in the nucleoprotein (NP) of pandemic strains A/Brevig Mission/1/1918 (1918) and A/Hamburg/4/2009 (pH1N1) that confer MxA resistance. These resistance-associated amino acids in NP differ between the two strains but form a similar discrete surface-exposed cluster in the body domain of NP, indicating that MxA resistance evolved independently. The 1918 cluster was conserved in all descendent strains of seasonal influenza viruses. Introduction of this cluster into the NP of the MxA-sensitive influenza virus A/Thailand/1(KAN-1)/04 (H5N1) resulted in a gain of MxA resistance coupled with a decrease in viral replication fitness. Conversely, introduction of MxA-sensitive amino acids into pH1N1 NP enhanced viral growth in Mx-negative cells. We conclude that human MxA represents a barrier against zoonotic introduction of avian influenza viruses and that adaptive mutations in the viral NP should be carefully monitored.
Swine influenza virus infection in different age groups of pigs in farrow-to-finish farms in Thailand
Nobuhiro Takemae, Sujira Parchariyanon, Ruttapong Ruttanapumma, Yasuaki Hiromoto, Tsuyoshi Hayashi, Yuko Uchida, Takehiko Saito
Virology Journal , 2011, DOI: 10.1186/1743-422x-8-537
Abstract: We conducted longitudinal monitoring in 6 farrow-to-finish farms in the central region of Thailand from 2008 to 2009. Nasal swabs and serum samples were collected periodically from clinically healthy pigs consisting of sows, fattening pigs, weaned piglets and pigs transferred from other farms. A total of 731 nasal swabs were subjected to virus isolation and 641 serum samples were subjected to detection of SIV antibodies against H1 and H3 subtypes using the hemagglutination inhibition test and ELISA. Twelve SIVs were isolated in this study and eleven were from piglets aged 4 and 8 weeks. Phylogenetical analysis revealed that SIVs isolated from different farms shared a common ancestor. Antibodies against SIVs were detected in fattening pigs on farms with no SIV isolation in the respective periods studied. These observations suggested that piglets aged 8 weeks or younger could be a main target for SIV isolation. Farm-to-farm transmission was suggested for farms where pigs from other farms are introduced periodically. In addition, antibodies against SIVs detected in fattening pigs could be a marker for SIV infection in a farm.The present study provided important information on SIV surveillance that will enable better understanding of SIV ecology in farrow-to-finish farms.Swine influenza virus (SIV) is one of the pathogens that cause respiratory diseases accompanied with coughing and sneezing in pigs [1]. This virus is considered an important pathogen not only from the viewpoint of animal health but also from that of public health [1-3]. Pigs can play the role of a 'mixing vessel' producing a novel influenza virus by genetic reassortment [4] as they have dual susceptibility to both human and avian influenza viruses [5]. Both receptors, namely, the sialic acid linked to galactose by an α2,6 linkage (SAα2,6Gal) for human viruses and an SAα2,3Gal for avian viruses, are expressed on epithelial cells of the tracheal and pulmonary structures of pigs [6,7]. The segmented nature
Efficacy of Influenza Vaccination and Tamiflu? Treatment – Comparative Studies with Eurasian Swine Influenza Viruses in Pigs  [PDF]
Ralf Duerrwald, Michael Schlegel, Katja Bauer, Théophile Vissiennon, Peter Wutzler, Michaela Schmidtke
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0061597
Abstract: Recent epidemiological developments demonstrated that gene segments of swine influenza A viruses can account for antigenic changes as well as reduced drug susceptibility of pandemic influenza A viruses. This raises questions about the efficacy of preventive measures against swine influenza A viruses. Here, the protective effect of vaccination was compared with that of prophylactic Tamiflu? treatment against two Eurasian swine influenza A viruses. 11-week-old pigs were infected by aerosol nebulisation with high doses of influenza virus A/swine/Potsdam/15/1981 (H1N1/1981, heterologous challenge to H1N1 vaccine strain) and A/swine/Bakum/1832/2000 (H1N2/2000, homologous challenge to H1N2 vaccine strain) in two independent trials. In each trial (i) 10 pigs were vaccinated twice with a trivalent vaccine (RESPIPORC? FLU3; 28 and 7 days before infection), (ii) another 10 pigs received 150 mg/day of Tamiflu? for 5 days starting 12 h before infection, and (iii) 12 virus-infected pigs were left unvaccinated and untreated and served as controls. Both viruses replicated efficiently in porcine respiratory organs causing influenza with fever, dyspnoea, and pneumonia. Tamiflu? treatment as well as vaccination prevented clinical signs and significantly reduced virus shedding. Whereas after homologous challenge with H1N2/2000 no infectious virus in lung and hardly any lung inflammation were detected, the virus titre was not and the lung pathology was only partially reduced in H1N1/1981, heterologous challenged pigs. Tamiflu? application did not affect these study parameters. In conclusion, all tested preventive measures provided protection against disease. Vaccination additionally prevented virus replication and histopathological changes in the lung of homologous challenged pigs.
Replication of avian, human and swine influenza viruses in porcine respiratory explants and association with sialic acid distribution
Sjouke GM Van Poucke, John M Nicholls, Hans J Nauwynck, Kristien Van Reeth
Virology Journal , 2010, DOI: 10.1186/1743-422x-7-38
Abstract: Compared to swine and human influenza viruses, replication of the AIVs was limited in all cultures but most strikingly in nasal and tracheal explants. Results of virus titrations were confirmed by quantification of infected cells using immunohistochemistry. By lectin histochemistry we found moderate to abundant expression of the human-like virus receptors in all explant systems but minimal binding of the lectins that identify avian-like receptors, especially in the nasal, tracheal and bronchial epithelium.The species barrier that restricts the transmission of influenza viruses from one host to another remains preserved in our porcine respiratory explants. Therefore this system offers a valuable alternative to study virus and/or host properties required for adaptation or reassortment of influenza viruses. Our results indicate that, based on the expression of Sia receptors alone, the pig is unlikely to be a more appropriate mixing vessel for influenza viruses than humans. We conclude that too little is known on the exact mechanism and on predisposing factors for reassortment to assess the true role of the pig in the emergence of novel influenza viruses.Pigs are important natural hosts for influenza A viruses, which are a major cause of acute respiratory disease. Influenza viruses of H1N1, H3N2 and H1N2 subtypes are enzootic in swine populations worldwide. Most of these swine influenza viruses are the product of genetic reassortment between viruses of human and/or avian and/or swine origin and their phylogeny and evolution are complex [1-3]. The swine influenza viruses circulating in Europe have a different origin and antigenic constellation than their counterparts in North America or Asia and within one region multiple lineages of a given subtype can be present [4,5]. Although natural infections of pigs with avian [6-10] or human influenza viruses [11,12] also occur, these viruses were rarely capable of establishing themselves as a stable lineage in pigs without under
2009 Swine-Origin Influenza A (H1N1) Resembles Previous Influenza Isolates  [PDF]
Carl Kingsford, Niranjan Nagarajan, Steven L. Salzberg
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0006402
Abstract: Background In April 2009, novel swine-origin influenza viruses (S-OIV) were identified in patients from Mexico and the United States. The viruses were genetically characterized as a novel influenza A (H1N1) strain originating in swine, and within a very short time the S-OIV strain spread across the globe via human-to-human contact. Methodology We conducted a comprehensive computational search of all available sequences of the surface proteins of H1N1 swine influenza isolates and found that a similar strain to S-OIV appeared in Thailand in 2000. The earlier isolates caused infections in pigs but only one sequenced human case, A/Thailand/271/2005 (H1N1). Significance Differences between the Thai cases and S-OIV may help shed light on the ability of the current outbreak strain to spread rapidly among humans.
Evolutionary genomics of the pandemic 2009 H1N1 influenza viruses (pH1N 1v)
Yanhua Qu, Ruiying Zhang, Peng Cui, Gang Song, Ziyuan Duan, Fumin Lei
Virology Journal , 2011, DOI: 10.1186/1743-422x-8-250
Abstract: Phylogenetic trees of eight gene segments showed that viruses sampled from human formed a well-supported clade, whereas swine and avian lineages were intermixed together. A new divergence swine sublineage containing gene segments of 2009 H1N1 viruses was characterized, which were closely related with swine viruses collected from USA and South Korea during 2004 to 2007 in six segments (PB2, PB1, PA, HA, NP and NS), and to swine viruses isolated from Thailand during 2004 to 2005 in NA and M. Substitution rates were varied drastically among eight segments and the average substitution rate was generally higher in 2009 H1N1 than in swine and human viruses (F2,23 = 5.972, P < 0.01). Similarly, higher dN/dS substitution ratios were identified in 2009 H1N1 than in swine and human viruses except M2 gene (F2, 25 = 3.779, P < 0.05). The ages of 2009 H1N1 viruses were estimated around 0.1 to 0.5 year, while their common ancestors with closest related swine viruses existed between 9.3 and 17.37 years ago.Our results implied that at least four reassortments or transmissions probably occurred before 2009 H1N1 viruses. Initial reassortment arose in 1976 and avian-like Eurasian swine viruses emerged. The second transmission happened in Asia and North America between 1988 and 1992, and mostly influenced six segments (PB2, PB1, PA, HA, NP and NS). The third reassortment occurred between North American swine and avian viruses during 1998 to 2000, which involved PB2 and PA segments. Recent reassortments occurred among avian-to-swine reassortant, Eurasian and classical swine viruses during 2004 to 2005. South Korea, Thailand and USA, were identified as locations where reassortments most likely happened. The co-circulation of multiple swine sublineages and special lifestyle in Asia might have facilitated mixing of diverse influenza viruses, leading to generate a novel virus strain.In April 2009, a new strain of human H1N1 influenza A viruses was identified in Mexico and USA, which caused
Comparison of Human-Like H1 ( -Cluster) Influenza A Viruses in the Swine Host  [PDF]
Janice R. Ciacci Zanella,Amy L. Vincent,Eraldo L. Zanella,Alessio Lorusso,Crystal L. Loving,Susan L. Brockmeier,Phillip C. Gauger,Bruce H. Janke,Marie R. Gramer
Influenza Research and Treatment , 2012, DOI: 10.1155/2012/329029
Abstract: Influenza A viruses cause acute respiratory disease in swine. Viruses with H1 hemagglutinin genes from the human seasonal lineage ( -cluster) have been isolated from North American swine since 2003. The objective of this work was to study the pathogenesis and transmission of -cluster H1 influenza viruses in swine, comparing three isolates from different phylogenetic subclusters, geographic locations, and years of isolation. Two isolates from the 2 subcluster, A/sw/MN/07002083/07 H1N1 (MN07) and A/sw/IL/00685/05 H1N1 (IL05), and A/sw/TX/01976/08 H1N2 (TX08) from the 1 sub-cluster were evaluated. All isolates caused disease and were transmitted to contact pigs. Respiratory disease was apparent in pigs infected with MN07 and IL05 viruses; however, clinical signs and lung lesions were reduced in severity as compared to TX08. On day 5 following infection MN07-infected pigs had lower virus titers than the TX08 pigs, suggesting that although this H1N1 was successfully transmitted, it may not replicate as efficiently in the upper or lower respiratory tract. MN07 and IL05 H1N1 induced higher serum antibody titers than TX08. Greater serological cross-reactivity was observed for viruses from the same HA phylogenetic sub-cluster; however, antigenic differences between the sub-clusters may have implications for disease control strategies for pigs. 1. Introduction Influenza A viruses are important infectious agents for humans, avian species, and many mammalian species, including swine. In swine, influenza virus causes an acute infection characterized by high morbidity and very low mortality rates [1]. Influenza viruses of the family Orthomyxoviridae have negative-sense single-stranded eight-segmented genome encoding for up to twelve structural and accessory proteins [2]. The triple reassortant internal gene constellation (TRIG) is the common backbone of the swine influenza viruses currently circulating in North America (for a review, see Vincent et al., 2008 [3]). Within the TRIG viruses, a dominant circulating genotype carries the HA and NA encoding genes of the human seasonal viruses of the H1 lineage (hu-like), identified from pigs in American and Canadian herds [4]. The HA genes of these viruses form the δ-cluster in phylogenetic analyses of HA genes from North American influenza A viruses of swine. Contemporary δ-cluster HA genes can be further divided into two sub-clusters, δ1 and δ2 [5]. Phylogenetically, the HA sequences of American and Canadian δ-cluster influenza A viruses appeared to have been derived from at least two independent human-to-pig transmission
Phylogenetic diversity and genotypic complexity of H1N1 subtype swine influenza viruses isolated in Mainland China  [cached]
Liu Yizhi,Wang Jing,Ji Jun,Chang Shuang
Virology Journal , 2012, DOI: 10.1186/1743-422x-9-289
Abstract: Background After the occurrence of 2009 pandemic H1N1, close attention has been paid to the H1N1 subtype swine influenza viruses (H1N1 SIV) by scientific communities in many countries. A large-scale sequence analysis of the NCBI Influenza Virus Resource Database on H1N1 SIVs submitted primarily by scientists in China during 1992 to 2011 was performed. The aims of this study were to elucidate the genetic and evolutionary characteristics of H1N1 SIVs, to identify and unify the lineages and genetic characteristics of the H1N1 SIVs isolated in mainland China. Results Most of the strains were isolated during the period of 2008 to 2010 from Guangdong and Shandong provinces, China. Based on the phylogenetic and genotypic analyses, all of the H1N1 SIV strains can be classified into 8 lineages and 10 genotypes. All strains were of the characteristics of low pathogenic influenza viruses. The viruses of different lineage are characterized with different amino acid residues at the receptor-binding sites. Viruses containing PB2 genes of the classical swine, early seasonal human and recent seasonal human lineage might be more infectious to human. Some genotypes were directly related with human influenza viruses, which include strains that harbored genes derived from human influenza viruses. Conclusions Phylogenetic diversity and complexity existed in H1N1 SIVs isolated in mainland China. These H1N1 SIV strains were closely related to other subtype influenza viruses, especially to human influenza viruses. Moreover, it was shown that, novel lineages and genotypes of H1N1 SIVs emerged recently in mainland China. These findings provided new and essential information for further understanding of the genetic and evolutionary characteristics and monitoring the H1N1 SIVs in mainland China.
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