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The H1N1 swine flu virus is compatible with a bird flu virus that is endemic in poultry in Asia and they can produce hybrid viruses packed with greater killing power, Chinese researchers warned on Monday.

The scientists made 127 hybrid viruses by mixing genes of the H1N1 and the avian H9N2 virus in a laboratory, and eight of the hybrids turned out to be more virulent than either parents when tested in mice.

The H1N1 pandemic of 2009 turned out to be milder than feared and human infections of H9N2 in China in the past are not known to have caused severe disease. But the experts said their hybrid offspring - or "reassortants" - cannot be casually dismissed.

"The main message is that the H1N1 can combine in certain ways with the H9N2 to create reassortants and some of the viruses had an increased pathogenicity comparing with the parent viruses in mice," lead author Jinhua Liu, of the College of Veterinary Medicine at the China Agricultural University in Beijing, wrote in an email to Reuters.

Liu and his colleagues, who published their findings in the Proceedings of the National Academy of Science, warned in their paper: "The possibility of novel pandemic strains being generated from reassortment between avian H9N2 and H1N1/2009 influenza viruses exists."

Flu viruses have eight gene segments and one of the segments is called the PA gene. Interestingly, all eight dangerous hybrids carried the PA gene belonging to the H1N1 parent virus.

The eight hybrid viruses caused severe pneumonia, edema and hemorrhaging in infected mice, the experts wrote.

Liu said their findings underscored the importance of monitoring hybrid viruses that arise from the H9N2 and H1N1.

The H9N2 is prevalent in China and large antibody surveys in the past found that between 13.7 percent and 37.2 percent of people sampled had prior infections by the H9N2.

"We should decrease the chance of infection with the two viruses in a (single) host," Liu wrote in his email.

Experts believe that a classic way for hybrid viruses to form is when different viruses meet and "marry" inside a single host, swapping genes. Humans and animals, such as pigs, can be efficient "mixing vessels."

Some scientists believe the pandemics of 1958 and 1968 occurred in such a fashion, killing up to two million and one million people worldwide, respectively.

SOURCE: bit.ly/eQqHrZ PNAS, online February 28, 2011.

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http://www.pnas.org/content/early/2011/ ... l.pdf+html

High genetic compatibility and increased pathogenicity of reassortants derived from avian H9N2 and pandemic H1N1/2009 influenza viruses
Yipeng Suna,1, Kun Qinb,1, Jingjing Wanga, Juan Pua, Qingdong Tanga, Yanxin Hua, Yuhai Bia,c, Xueli Zhaoa, Hanchun Yanga, Yuelong Shub, and Jinhua Liua,d,2
+ Author Affiliations

aKey Laboratory of Zoonosis of Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing 100193, China;
bChinese National Influenza Center, State Key Laboratory for Molecular Virology and Genetic Engineering, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing 100052, China;
dThe Shandong Animal Disease Control Center, Jinan, Shandong 250022, China; and
cCAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China
Edited by Peter Palese, Mount Sinai School of Medicine, New York, NY, and approved January 28, 2011 (received for review December 21, 2010)

↵1Y. Sun and K.Q. contributed equally to this work.

2To whom correspondence should be addressed. E-mail: ljh@cau.edu.cn.
Abstract
H9N2 influenza viruses have been circulating worldwide in multiple avian species and repeatedly infecting mammals, including pigs and humans, posing a significant threat to public health. The coexistence of H9N2 and pandemic influenza H1N1/2009 viruses in pigs and humans provides an opportunity for these viruses to reassort. To evaluate the potential public risk of the reassortant viruses derived from these viruses, we used reverse genetics to generate 127 H9 reassortants derived from an avian H9N2 and a pandemic H1N1 virus, and evaluated their compatibility, replication ability, and virulence in mice. These hybrid viruses showed high genetic compatibility and more than half replicated to a high titer in vitro. In vivo studies of 73 of 127 reassortants revealed that all viruses were able to infect mice without prior adaptation and 8 reassortants exhibited higher pathogenicity than both parental viruses. All reassortants with higher virulence than parental viruses contained the PA gene from the 2009 pandemic virus, revealing the important role of the PA gene from the H1N1/2009 virus in generating a reassortant virus with high public health risk. Analyses of the polymerase activity of the 16 ribonucleoprotein combinations in vitro suggested that the PA of H1N1/2009 origin also enhanced polymerase activity. Our results indicate that some avian H9-pandemic reassortants could emerge with a potentially higher threat for humans and also highlight the importance of monitoring the H9-pandemic reassortant viruses that may arise, especially those that possess the PA gene of H1N1/2009 origin.

Footnotes
Author contributions: Y. Sun, J.P., and J.L. designed research; Y. Sun, K.Q., J.W., Q.T., Y.H., Y.B., and X.Z. performed research; K.Q. and J.L. contributed new reagents/analytic tools; Y. Sun, K.Q., J.P., Q.T., Y.H., H.Y., Y. Shu, and J.L. analyzed data; and Y. Sun, K.Q., J.W., and J.L. wrote the paper.
The authors declare no conflict of interest.
The sequences reported in this paper have been deposited in the GenBank database [accession nos. GQ373026 (HB08, PB2 gene), GQ373043 (HB08, PB1 gene), GQ373060 (HB08, PA gene), GQ373077 (HB08, HA gene), GQ373094 (HB08, NP gene), GQ373111 (HB08, NA gene), GQ373128 (HB08, M gene), GQ373144 (HB08, NS gene), HQ698624 (BJ09, PB2 gene), HQ698625 (BJ09, PB1 gene), HQ698626 (BJ09, PA gene), HQ698627 (BJ09, HA gene), HQ698628 (BJ09, NP gene), HQ698629 (BJ09, NA gene), HQ698630 (BJ09, M gene), and (BJ09, NS gene)].
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/p ... pplemental.

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Our findings demonstrated that the PA gene from the BJ09
virus may significantly contribute to the pathogenicity of avian–
human reassortants. H9N2 virus that was replaced only by
a single PA gene from pandemic H1N1 virus could substantially
increase its pathogenicity in mice. Although the introduction of
the PA gene from pandemic H1N1/2009 virus into avian H9N2
virus did not necessarily result in a more pathogenic phenotype,
our results revealed that the PA gene of H1N1/2009 origin is
a prerequisite for the emergence of reassortants with increased
pathogenicity. It is known that the PA gene of pandemic H1N1
(2009) virus was of North American avian origin (16, 31). Thus,
the pandemic PA gene may be compatible with the other gene
segments from avian H9N2 viruses as a prerequisite for the increase
of viral pathogenicity. Furthermore, a previous study
found that the introduction of a human influenza PA gene into an
avian polymerase gene could overcome restriction of avian
polymerase in human cells (32). Similarly, in the present study,
the PA gene of pandemic H1N1/2009 origin could increase the
polymerase activity of avian-pandemic RNP, especially for the
HPB2HPB1BPAHNP combination. Therefore, the PA gene of
pandemic H1N1/2009 origin that was adapted to humans might
contribute to the high polymerase activity leading to enhanced
virulence of the reassortants in mice.

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And here's what CIDRAP has to say.....so next time the conspiracy theory people will say the virus came from a lab and quote these articles....

Mar 2, 2011 (CIDRAP News) – Chinese researchers who tested reassortants that combined the 2009 H1N1 virus with H9N2, a subtype that commonly circulates in birds, found that several were more pathogenic then the parent viruses, which they said could pose a pandemic threat.

Their experiments also found that of 127 reassortants between the two viruses, as many as 57.5% had a high ability to replicate, similar to the two parent viruses, which suggests that the two viruses have a high genetic compatibility. The findings appeared in the Proceedings of the National Academy of Sciences. The report was edited by Dr Peter Palese, a well-known virologist at Mount Sinai School of Medicine in New York City.

Though H9N2 is a low-pathogenic virus, it has also been found in pigs, which infectious disease experts have said could be a "mixing vessel" for animal and human flu viruses, producing novel flu viruses with pandemic potential.

Human infections with H9N2 have been reported, and the World Health Organization (WHO) includes the virus alongside H5N1 in its annual recommendations for pandemic flu vaccine candidate viruses.

Unpacking virulence differences
Using reverse genetics, the study group attempted to make all possible 127 reassortants from an avian H9N2 influenza virus and the 2009 H1N1 virus. Then they categorized each into one of four groups based on replication ability.

A total of 73 reassortants showed a high ability to replicate, and the group evaluated the pathogenicity of all of them in mice. Based on those findings, they sorted the viruses into three groups that varied by how sick the mice got. Eight of the reassortants caused more severe disease, based on clinical observation such as ruffled coat, lethargy, and dyspnea, and microscopic signs in lung tissue, which included interstitial pneumonia and bronchopneumonia, edema, hemorrhage, epithelial cell dropout, and infiltration of inflammatory cells.

All eight of the most pathogenic reassortants had the polymerase acid (PA) gene segment from the 2009 H1N1 virus, which the authors suggest is required for the emergence of the most virulent reassortants they tested. Further analysis showed that the basic polymerase 1 (PB1) gene of the 2009 H1N1 virus usually attenuated the pathogenicity of the reassortants, and the neuraminidase of that parent virus typically increased their virulence.

Projecting illness impacts
Though the more virulent reassortants were a major concern, the less pathogenic ones that emerged are also worth noting, the authors state, because they could circulate undetected in mammals, and mutation or further reassortment could also pose a pandemic threat.

Not all of the reassortants that had the PA gene segment from the 2009 H1N1 virus were more virulent that their parent viruses, which the investigators said suggests that other gene segments play a role in pathogenicity.

They said their examination of the sickest mice showed no evidence of systemic spread, but all viruses replicated efficiently in the lungs and showed high polymerase activity. "These results suggested that a high virus load and high polymerase activity were important factors for the virulence of the reassortants in mice," they wrote.

The group concluded that reassortants between H9N2 and pandemic H1N1 could pose a public health threat and that the PA gene segment findings in the most virulent ones could serve as a marker for identifying H9 reassortants that present the greatest risks.

New study plots out H9N2 family tree
In a related development, researchers said that the extensive reassortments that the H9N2 flu virus has undergone shows it has the potential for continued influenza outbreaks in poultry and epidemics in humans.

A group from China that included two scientists from the US Department of Agriculture conducted a sequence analysis of 571 viral genomes from a flu virus database to pinpoint the subtype's genetic and evolutionary characteristics.

They found 74 separate lineages, which showed host and geographic differences. Genotype analysis revealed at least 98 different ones, which fell into seven series according to their hemagglutinin lineages.

Analyses of the internal genes found that H9N2 viruses are closely related to H3, H4, H5, H7, H10, and H14 subtypes.

Because H9N2 viruses have undergone extensive changes that produced many reassortants and genotypes, continued circulation in diverse hosts could lead to future outbreaks in poultry and humans.

They wrote that their analyses offers the world's first full characterization of H9N2's phylogeny and genetic diversity, and they proposed a nomenclature system for identifying all of the subtype's lineages and genotypes that could be helpful for epidemiology, evolution, and ecology studies.

New information from the study suggests that the geographic distribution of H9N2 viruses is larger than earlier studies reported, spanning Asia, the Middle East, Europe, Africa, and North America, the authors wrote. Some North American H9N2 viruses have links to Asia and Europe, which they said suggests that the H9N2 viruses have become more complicated.

The phylogenic analysis suggests that the H9N2 virus is very diverse, with permanent lineages established in Asian poultry and with frequent appearances in pigs, especially in China.

Sun Y, Qin K, Wang J, et al. High genetic compatibility and increased pathogenicity of reassortants derived from avian H9N2 and pandemic H1N1/2009 influenza viruses. Proc Natl Acad Sci 2011 (published online Feb 28) [Abstract]

Dong G, Luo J, Zhang H, et al. Phylogenetic diversity and genotypical complexity of H9N2 influenza A virus revealed by genomic sequence analysis. PLoS One 2011 Feb 28;6(2):[Full text]