Nucleotide sequence analysis of the HA1 coding portion of the haemagglutinin gene of swine H1N1 influenza viruses.

The nucleotide and deduced amino acid sequences coding for the HA1 portion of the haemagglutinin (HA) genes of three swine influenza viruses were determined and compared with published HA sequence data for human H1N1 influenza viruses. Sequence differences between the classic swine influenza HAs sw37 (A/swine/29/37) and NJ76 (A/New Jersey/11/76) were randomly distributed in the molecule without being confined to antigenic sites. In contrast, sequence differences between the HAs of sw37 and the antigenically atypical strains sw38 (A/swine/Northern Ireland/38) and sw39 (A/swine/Cambridge/39) were clustered in hypervariable regions, similar to the pattern of changes that was present between sw37 and the human strains PR834 (A/PR/8/34) and WSN33 (A/WSN/33). Sequence homologies of the European swine influenza strains (sw38, sw39) were higher with the HAs of the human strains (PR834, WSN33) than with the classic swine influenza HAs (sw37, NJ76). Phylogenetic analysis showed that the HA genes of these two European swine influenza strains emerged from a different evolutionary lineage of H1 HAs than the HAs of classic swine influenza strains.     

Characterization of the pathogenicity of members of the newly established H9N2 influenza virus lineages in Asia

The reported transmission of avian H9N2 influenza viruses to humans and the isolation of these viruses from Hong Kong poultry markets lend urgency to studies of their ecology and pathogenicity. We found that H9N2 viruses from North America differ from those of Asia. The North American viruses, which infect primarily domestic turkeys, replicated poorly in inoculated chickens. Phylogenetic analysis of the hemagglutinin and nucleoprotein genes indicated that the Asian H9N2 influenza viruses could be divided into three sublineages. Initial biological characterization of at least one virus from each lineage was done in animals. Early isolates of one lineage (A/Chicken/Beijing/1/94, H9N2) caused as high as 80% mortality rates in inoculated chickens, whereas all other strains were nonpathogenic. Sequence analysis showed that some isolates, including the pathogenic isolate, had one additional basic amino acid (A-R/K-S-S-R-) at the hemagglutinin cleavage site. Later isolates of the same lineage (A/Chicken/Hong Kong/G9/97, H9N2) that contains the PB1 and PB2 genes similar to Hong Kong/97 H5N1 viruses replicated in chickens, ducks, mice, and pigs but were pathogenic only in mice. A/Quail/Hong Kong/G1/97 (H9N2), from a second lineage that possesses the replicative complex similar to Hong Kong/97 H5N1 virus, replicated in chickens and ducks without producing disease signs, was pathogenic in mice, and spread to the brain without adaptation. Examples of the third Asian H9N2 sublineage (A/Chicken/Korea/323/96, Duck/Hong Kong/Y439/97) replicated in chickens, ducks, and mice without producing disease signs. The available evidence supports the notion of differences in pathogenicity of H9N2 viruses in the different lineages and suggests that viruses possessing genome segments similar to 1997 H5N1-like viruses are potentially pathogenic in mammals.     

Evolutionary pathways of the PA genes of influenza A viruses

Nucleotide sequences of the PA genes of influenza A viruses, isolated from a variety of host species, were analyzed to determine the evolutionary pathways of these genes and the host specificity of the genes. Results of maximum parsimony analysis of the nucleotide sequences indicate at least five lineages for the PA genes. Those from human strains represent a single lineage, whereas the avian genes appear to have evolved as two lineages--one comprising genes from many kinds of birds (e.g., chickens, turkeys, shorebirds, and ducks) and the other comprising only genes from gulls. H3N2 swine influenza virus PA genes are closely related to the currently circulating duck virus PA gene. By contrast, the H1N1 swine and equine virus PA genes appear to have evolved along independent lineages. Comparison of predicted amino acid sequences disclosed 10 amino acid substitutions in the PA proteins of all avian and H3N2 swine viruses that distinguished them from human viruses. The H1N1 swine viruses seem to be chimeras between human and avian viruses and they contain 8 amino acids not shared by other viruses. The equine viruses also appear to show their own amino acid substitutions. These findings indicate that the PA genes of influenza A viruses have evolved in different pathways defined by apparently unique amino acid substitutions and host specificities. They also indicate that influenza A viruses have been transmitted from avian to mammalian species.     

Genetic evolution of swine influenza A (H3N2) viruses in China from 1970 to 2006

Pigs are susceptible to both human and avian influenza viruses and have been proposed to be intermediate hosts, or mixing vessels, for the generation of pandemic influenza viruses through reassortment or adaptation to the mammalian host. In this study, we summarize and report for the first time the coexistence of wholly human-like H3N2 viruses, double-reassortant H3N2 viruses, and triple-reassortant H3N2 viruses in pigs in China by analyzing the eight genes of swine influenza A (H3N2) viruses found in China from 1970 to 2006. In 1970, the first wholly human-like H3N2 (Hong Kong/68-like) viruses were isolated from pigs in Taiwan, and then in the next years Victoria/75-like, Sydney/97-like, New York/99-like, and Moscow/99-like swine H3N2 viruses were regularly isolated in China. In the 1980s, two triple-reassortant viruses were isolated from pigs. Recently, the double-reassortant viruses containing genes from the human (HA and NA) and avian (PB2, PB1, PA, NP, M, and NS) lineages and the triple-reassortant viruses containing genes from the human (HA and NA), classical swine (NP), and avian (PB2, PB1, PA, M, and NS) lineages emerged in pigs in China. The coexistence of wholly human-like and reassortant viruses provides further evidence that pigs serve as intermediate hosts, or mixing vessels, and emphasizes the importance of reinforcing swine influenza virus surveillance in China.     

Genetic Conservation of Hemagglutinin Gene of H9 Influenza Virus in Chicken Population in Mainland China

The hemagglutinin (HA) genes of 12 H9N2 influenza virus strains isolated from chickens in Mainland China during the period 1995–2002 were genetically analyzed. All the isolates possessed the same amino acid motif -R-S-S-R/G-L- at the cleavage site of HA. Except for the conserved amino acids, as is the case in the other avian influenza viruses, located in the receptor binding site, all of the 12 isolates possessed N at amino acid position 183; A, T, or V at position 190; K at position 137, whereas the representative strains of the other lineage (except Dk/HK/Y280/97-like lineage) virus of H9N2 viruses had H, E, and R at these positions respectively. These could be considered as the partial molecular markers of the H9 viruses isolated from chickens in Mainland China. Phylogenetic analyses showed HA genes of these isolates belonged to that of A/duck/Hong Kong/Y280/97-like virus lineage. No A/quail/Hong Kong/Gl/97-like virus was found in chicken, population since the outbreak of H9N2 influenza in Mainland China in 1992. The available evidence indicates that HA genes of H9 influenza virus circulating in Mainland China during the past years were well conserved.     

Potency of an inactivated influenza vaccine prepared from A/duck/Hong Kong/960/1980 (H6N2) against a challenge with A/duck/Vietnam/OIE-0033/2012 (H6N2) in mice

H6 influenza viruses are prevalent in domestic and wild birds in Eurasian countries and have been isolated from pigs and a human. To prepare for an influenza pandemic, we have established an influenza virus library consisting of more than 1,300 influenza virus strains, including 144 combinations of 16 hemagglutinin and 9 neuraminidase subtypes. H6 viruses in the library were classified into Early, Group II, Group III, and W312 sublineages and the North America lineage on the basis of their phylogenetic features. Chicken antisera to A/duck/Hong Kong/960/1980 (H6N2) of the Early sublineage broadly reacted with viruses of different sublineages in a hemagglutinin inhibition test. A whole inactivated virus particle vaccine was prepared from A/duck/Hong Kong/960/1980 (H6N2) which was stocked in the influenza virus library. The potency of this vaccine against A/duck/Vietnam/OIE-0033/2012 (H6N2), which belongs to a different sublineage, was evaluated in mice. The test vaccine was sufficiently potent to induce an immune response that reduced the impact of disease caused by a challenge with A/duck/Vietnam/OIE-0033/2012 (H6N2) in mice. The present results indicate that the whole inactivated virus particle vaccine prepared from a virus strain in the influenza virus library is useful as a vaccine against pandemic influenza.     

Studies on the origin of pandemic influenza: III. Evidence implicating duck and equine influenza viruses as possible progenitors of the Hong Kong strain of human influenza

Two strains of influenza virus isolated from horses and ducks in 1963, A/equine/Miami/1/63 (Heq2 Neq2) and A/duck/Ukraine/1/63 (Hav7 Neq2) were found to possess hemagglutinin subunits which cross-reacted in hemagglutination-inhibition and immunodiffusion tests with those of the Hong Kong strain of human influenza A/Hong Kong/1/68 (H3 N2).Peptide maps of the heavy polypeptide chains from the hemagglutinin subunits of these three strains showed a number of differences, but maps of the light chains were almost identical, indicating that the light polypeptide chains from the hemagglutinin subunits of these animal, avian and human viruses had practically the same amino acid sequence.One explanation of these results is that the three viruses arose, by genetic recombination, from a common ancestor.     

我国猪群中H9N2亚型毒株HA和NA基因特性的研究

目的 了解我国内地从猪中分离到H9N2亚型毒株HA和NA基因来源及它们使猪致病的原因。方法 用PCR扩增目的基因，与P^GEM-T Easy Vector4℃过夜连接，重组质粒转化DH-10β细菌，筛选阳性菌落，酶切鉴定，测序。然后，进行进化树分析。结果 两株猪H9N2毒株HA蛋白分子上第226位上氨基酸为L，这与从人和猪所分离出的H9N2毒株相同，其连接肽属对禽致病的毒株，但它们的序列为R-L-S-R，而不是R-S-S-R；其NA蛋白茎区第62～64位存在掉失，这与A／Shaoguarn/408／98，A／Swine／Hong Kong／9／98及A／Duck／Hong Kong／y280／97(H9N2)毒株相同；HA与NA基因进化树分析表明，两株猪H9N2毒株的HA基因接近于A／Chicken／Hong Kong／G23／97和A／Chicken／Hong Kong／G9／97．而NA基因接近于A／Shaoguan／408／98毒株。结论 两株猪H9N2亚型毒株的HA和NA基因可能性最大来自禽H9N2毒株。由于其HA蛋白分子上连接肽氨基酸序列发生替换，可能造成了它们对猪具有致病性。禽H9N2毒株NA蛋白茎区氨基酸掉失，造成了它们能直接感染猪。     

Genetic analysis of avian influenza A viruses isolated from domestic waterfowl in live-bird markets of Hanoi, Vietnam, preceding fatal H5N1 human infections in 2004

The first known cases of human infection with highly pathogenic avian influenza (HPAI) H5N1 viruses in Vietnam occurred in late 2003. However, HPAI H5N1 and low-pathogenic avian influenza (LPAI) H5N2 and H9N3 viruses were isolated from domestic waterfowl during live-bird market (LBM) surveillance in Vietnam in 2001 and 2003. To understand the possible role of these early viruses in the genesis of H5N1 strains infecting people, we performed sequencing and molecular characterization. Phylogenetic analysis revealed that the hemagglutinin (HA) genes of two geese HPAI H5N1 strains belonged to clade 3, and their surface glycoprotein and replication complex genes were most closely related (98.5–99.7% homologous) to A/duck/Guangxi/22/01 (H5N1) virus, detected contemporarily in southern China, whilst the M and NS genes were derived from an A/duck/Hong Kong/2986.1/00 (H5N1)-like virus. The H5 HA gene of the duck HPAI H5N1 strain belonged to clade 5 and acquired a gene constellation from A/quail/Shantou/3846/02 (H5N1), A/teal/China/2978.1/02 (H5N1) and A/partridge/Shantou/2286/03 (H5N1)-like viruses. The phylogenetic analysis further indicated that all eight gene segments of goose and duck HPAI H5N1 and LPAI H5N2 viruses were distinct from those of H5N1 clade-1 viruses known to have caused fatal human infections in Vietnam since late 2003. The duck H9N3 isolates derived genes from aquatic-bird influenza viruses, and their H9 HA belonged to the Korean lineage. The PB2 gene of A/duck/Vietnam/340/01 (H9N3) virus had lysine at position 627. Based on the molecular characterization of specific amino acid residues in the surface and relevant internal protein-coding genes, the Vietnamese H5N1 and H9N3 virus isolates indicated specificity to avian cell surface receptor and susceptibility for currently licensed anti-influenza A virus chemotherapeutics. Our findings suggest that the H5N1 and H5N2 viruses that circulated among geese and ducks in LBMs in Hanoi, Vietnam, during 2001 and 2003 were not the immediate ancestors of the clade-1 viruses associated with fatal human infections in Vietnam. The clade-1 HPAI H5N1 viruses were independently introduced into Vietnam.     

Further genetic evidence for maintenance of early Hong Kong-like influenza A(H3N2) strains in swine until 1976

The oligonucleotide map of the whole RNA of A/swine/Hong Kong/3/76 (H3N2) virus showed a relationship to, but considerable differences from, the maps of human isolates of influenza A(H3N2) with which this isolate antigenically cross-reacted. Comparison of the individual oligonucleotide spots of whole virus RNAs confirmed previous results of antigenic analysis that A/swine/Hong Kong/3/76 virus was more similar to an early A/Hong Kong/68 virus than to later H3N2 viruses which circulated in man during 1976. On the other hand, another swine isolate, A/swine/Hong Kong/4/76, showed a quite similar oligonucleotide map to that of the contemporary prevalent A/Victoria/75-like viruses to which this strain was reported to be antigenically similar. Comparison of oligonucleotide maps of individual RNA segments indicated that all genes of the A/swine/Hong Kong/3/76 virus were derived from a human H3N2 virus. The findings provide biochemical evidence that A/swine/Hong Kong/3/76 virus represents a 1968 Hong Kong-like virus that underwent genetic mutation without extensive change of its antigenicity during maintenance in the swine population.     

Phylogenetic Analysis of Hemagglutinin and Neuraminidase Genes of H9N2 Viruses Isolated from Migratory Ducks

Genetic analysis indicated that the pandemic influenza strains derived from wild aquatic birds harbor viruses of 15 hemagglutinin (HA) and 9 neuraminidase (NA) antigenic subtypes. Surveillance studies have shown that H9N2 subtype viruses are worldwide in domestic poultry and could infect mammalian species, including humans. Here, we genetically analyzed the HA and NA genes of five H9N2 viruses isolated from the migratory ducks in Hokkaido, Japan, the flyway of migration from Siberia during 1997–2000. The results showed that HA and NA genes of these viruses belong to the same lineages, respectively. Compared with those of A/quail/Hong Kong/G1/97-like and A/duck/Hong Kong/Y280/97-like viruses, HA and NA of the migratory duck isolates had a close relationship with those of H9N2 viruses isolated from the chicken in Korea, indicating that the Korea H9N2 viruses might be derived from the migratory ducks. The NA genes of the five isolates were located in the same cluster as those of N2 viruses, which had caused a human pandemic in 1968, indicating that the NA genes of the previous pandemic strains are still circulating in waterfowl reservoirs. The present results further emphasize the importance of carrying out molecular epidemiological surveillance of H9N2 viruses in wild ducks to obtain more information for the future human influenza pandemics preparedness.     

Origin of the hemagglutinin gene of H3N2 influenza viruses from pigs in China

Influenza viruses of the H3N2 subtype similar to Aichi/2/68 and Victoria/3/75 persist in pigs many years after their antigenic counterparts have disappeared from humans (Shortridge et al. (1977). Science 19, 1454-1455). To provide information on the mechanism of conservation of these influenza viruses in pigs, the hemagglutinin (HA) of four isolates from swine derived from Taiwan and Southern China were analyzed antigenically and genetically. The reactivity pattern of these viruses with a panel of monoclonal antibodies indicates that the HAs of these swine viruses were antigenically closely related to duck H3 and early human H3 viruses. Sequence analysis of the H3 genes from three swine viruses revealed that the swine H3 genes are more closely related to the duck genes than to early human H3 virus (A/Aichi/2/68). The degree of sequence homology of these genes is extremely high (more than 96.5%). Furthermore, the deduced amino acid sequence of the three swine HAs at residues 226 to 228 in the proposed receptor-binding site is Gln-Ser-Gly and is common with the majority of avian influenza viruses. These findings indicate that these H3 viruses may have been introduced into pigs from ducks. The HA gene of the fourth swine influenza virus from Southern China was genetically equally related to avian and early human H3 strains although the sequence through the receptor-binding pocket (226-228) was typical of a human H3 virus, suggesting that either this swine HA gene was derived from ducks or an early human H3 virus was introduced into the pig population where the virus accumulated substantial mutations. The present strains revealed genetic heterogeneity of swine H3 influenza viruses in nature.     

Genome-sequenee Analysis of the Pathogenic H5N1 Avian Influenza A Virus Isolated in China in 2004

Analysis of the sequences of the genome of the avian influenza A/chicken/Hubei/327/2004 (H5N1) virus, isolated from a poultry farm during the outbreak of avian influenza (AI) in Hubei Province, central China, in the spring of 2004, revealed that the hemagglutinin (HA) gene of the virus was genetically similar to those of the H5 highly pathogenic avian influenza virus (HPAI). Notably, the neuraminidase gene of the virus had a 20-amino acid deletion in the stalk region and a 5-amino acid deletion in the NS gene which belonged to allele B. Furthermore, the internal genes (PB2, PA, NP, M2) of the A/chicken/Hubei/327/2004 virus with the particular amino acid residues were more closely related to H5N1 viruses of 2000–2003 isolated in Hong Kong and the AIV of Thailand and Vietnam in 2004, but less likely to evolve from the viruses of Hong Kong 1997. Finally, our results demonstrated that the influenza A/chicken/Hubei/327/2004 (H5N1) virus was similar to those of the AI viruses isolated from Hong Kong (2000–2003), Vietnam, and Thailand rather than the viruses from the 1997 lineage of Hong Kong and with closest genetic relatives to the influenza A/Chicken/Hong Kong/61.9/02 (H5N1) virus. These data suggest that the influenza A/chicken/Hubei/327/2004 (H5N1) virus which circulated in central China derived its internal gene from a virus similar to the influenza A/Chicken/Hong Kong/61.9/02 (H5N1) virus.     

Swine infection with H9N2 influenza viruses in China in 2004

In 2004, H9N2 influenza A viruses were isolated from pigs with respiratory syndrome in commercial swine farms in Henan province, China. Antigenic and genetic characterization were performed for seven swine H9N2 influenza viruses. The hemagglutinin antigenicity of swine H9N2 viruses was similar to those of avian H9N2 viruses of A/duck/Hong Kong/Y280/1997 (Dk/HK/Y280/97)-like sublineage prevalent in China. It is noteworthy that the neuraminidase of these isolates had no deletions in the stalk, which was seldom observed in those viruses of Dk/HK/Y280/97-like sublineage. Genetic analysis revealed that all seven isolates had an -R-S-S-R- motif at the HA cleavage site, which was the same as those of Dk/HK/Y280/97-like viruses established in avian population in China. Phylogenetic analyses showed that the seven swine H9N2 viruses were completely derived from avian influenza viruses of Dk/HK/Y280/97-like sublineage. The present results indicated that avian-to-pig interspecies transmission of H9N2 viruses continued to exist in China through 2004; therefore, surveillance of swine influenza should be given a high priority. Yan-Long Cong, Chun-Feng Wang and Chun-Mei Yan have contributed equally to this work. (i) All the authors have agreed to its submission and are responsible for its contents and (ii) all the authors have agreed that Yanlong Cong may act on their behalf regarding any subsequent processing of the paper.     

Characterization of a 1980-swine recombinant influenza virus possessing H1 hemagglutinin and N2 neuraminidase similar to that of the earliest Hong Kong (H3N2) virus

A recombinant (H1N2, formerly Hsw 1N2), A/swine/Ehime/1/80 was found to possess antigenic, biological and genomic characteristics different from those of a previous A/swine/Kanagawa/2/78 (H1N2) strain. Five monoclonal antibodies to A/NJ/8/76 definitely differentiated the hemagglutinin molecules of the former virus from the latter, showing that these viruses differed, at least, at two antigenic determinants. Neuraminidase-inhibition tests with monoclonal antibodies to different H2N2 and H3N2 viruses revealed that the A/swine/Ehime/1/80 strain contained a neuraminidase very similar to that of the late human Asian (H2N2) and the earliest Hong Kong (H3N2) viruses. Growth comparison of swine and human isolates indicated that A/swine/Ehime/1/80 and A/swine/Shizuoka/1/78 (H1N1) failed to grow at 42 degrees C, while A/swine/Kanagawa/2/78 and its possible parental virus, A/swine/Kanagawa/4/78 (H1N1) replicated efficiently at this stringent temperature. These results revealed that the viruses having growth characteristics similar to those of avian influenza virus were present in the swine population. RNA analysis by oligonucleotide mapping suggested that A/swine/Ehime/1/80 may be a recombinant between A/swine/Shizuoka/1/78-like and A/Aichi/2/68 (H3N2)-like viruses. To further determine the gene constellation of this recombinant virus, DNA-RNA hybridization was performed by using DNA segments complementary for swine (H1N1) virus RNA and the entire RNAs of three viruses. The molecular hybridization could define the genomic composition of the recombinant, indicating that only the neuraminidase gene of this virus is derived from the earliest Hong Kong (H3N2)-like virus and remaining seven genes from swine (H1N1) virus.     

Characterization of a swine-like reassortant H1N2 influenza virus isolated from a wild duck in the United States

An H1N2 influenza virus (A/Duck/North Carolina/91347/01) (Dk/NC) was isolated from a wild duck in the United States in 2001. Genetic analyses showed that this duck virus has the same human/classical swine/avian reassortant genotype as the H1N2 viruses that have been isolated from pigs and turkeys in the US since 1999. Phylogenetic analyses of each gene segment further confirmed that the Dk/NC virus is closely related to the domestic animal H1N2 isolates. In particular, Dk/NC is most closely related to a swine H1N2 virus also isolated in North Carolina. These two viruses and a phylogenetically-defined subset of additional swine H1N2 viruses share a common mutation in the Sb antigenic site on the hemagglutinin protein. The recovery of Dk/NC from a wild bird raises concerns for further widespread distribution of these H1N2 viruses via waterfowl migration.     

Genetic characterization of H3N2 influenza viruses isolated from pigs in North America, 1977-1999: evidence for wholly human and reassortant virus genotypes

Since 1998, H3N2 viruses have caused epizootics of respiratory disease in pigs throughout the major swine production regions of the U.S. These outbreaks are remarkable because swine influenza in North America had previously been caused almost exclusively by H1N1 viruses. We sequenced the full-length protein coding regions of all eight RNA segments from four H3N2 viruses that we isolated from pigs in the Midwestern U.S. between March 1998 and March 1999, as well as from H3N2 viruses recovered from a piglet in Canada in January 1997 and from a pig in Colorado in 1977. Phylogenetic analyses demonstrated that the 1977 Colorado and 1997 Ontario isolates are wholly human influenza viruses. However, the viruses isolated since 1998 from pigs in the Midwestern U.S. are reassortant viruses containing hemagglutinin, neuraminidase and PB1 polymerase genes from human influenza viruses, matrix, non-structural and nucleoprotein genes from classical swine viruses, and PA and PB2 polymerase genes from avian viruses. The HA proteins of the Midwestern reassortant swine viruses can be differentiated from those of the 1995 lineage of human H3 viruses by 12 amino acid mutations in HA1. In contrast, the Sw/ONT/97 virus, which did not spread from pig-to-pig, lacks 11 of these changes.     

H5N1 influenza viruses isolated from geese in Southeastern China: evidence for genetic reassortment and interspecies transmission to ducks

The H5N1 viruses (H5N1/97) associated with the "bird-flu" incident in the Hong Kong SAR have not been isolated since the slaughter of poultry in December 1997 brought that outbreak to an end. Recent evidence points to this virus as having arisen through a reassortment of a number of precursor avian viruses and a virus related to Goose/Guangdong/1/96 (H5N1) (Gs/Gd/96) was the likely donor of the H5 hemagglutinin. We characterize the Goose/Guangdong/1/96-like viruses isolated from geese and ducks imported into Hong Kong in the year 2000. Antigenically and genetically, these recent H5N1 viruses fall into two groups, one mainly associated with geese, and the other, recently transmitted to ducks. Further, viruses isolated from a goose and a duck in December 2000 have acquired NS, PA, M, and PB2 genes from the aquatic avian influenza gene pool through reassortment. For pandemic preparedness, it is important to monitor whether these reassortant viruses have the capacity for interspecies transmission to terrestrial poultry or mammals.     

Genetic characterization of H1 avian influenza viruses isolated from migratory birds and domestic ducks in Korea

H1 avian influenza viruses (AIVs) isolated from migratory birds and domestic ducks from 2003 to 2007 were analyzed to determine their genetic relationship. Phylogenic analysis with nucleotide sequences of all eight gene segments showed that 13 H1 AIVs from migratory birds and domestic ducks belonged to Eurasian avian lineages and were closely related to each other. Compared with H1 influenza viruses of swine or human origin in Korea, there was no evidence of reassortment among the human, swine, and avian hosts. Our results show that H1 AIVs isolated in Korea from 2003 to 2007 were genetically stable. However, continued surveillance is needed considering the role of migratory birds and domestic duck as a source of AIVs.     

Genetic characterization of the pathogenic influenza A/Goose/Guangdong/1/96 (H5N1) virus: similarity of its hemagglutinin gene to those of H5N1 viruses from the 1997 outbreaks in Hong Kong.

Analysis of the sequences of all eight RNA segments of the influenza A/G oose/Guangdong/1/96 (H5N1) virus, isolated from a sick goose during an outbreak in Guangdong province, China, in 1996, revealed that the hemagglutinin (HA) gene of the virus was genetically similar to those of the H5N1 viruses isolated in Hong Kong in 1997. However, the remaining genes showed greater similarity to other avian influenza viruses. Notably, the neuraminidase gene did no have the 19-amino-acid deletion in the stalk region seen in the H5N1 Hong Kong viruses and the NS gene belonged to allele B, while that of the H5N1 Hong Kong viruses belonged to allele A. These data suggest that the H5N1 viruses isolated from the Hong Kong outbreaks derived their HA genes from a virus similar to the A/Goose/Guangdong/1/96 virus or shared a progenitor with this goose pathogen.