Swine influenza virus A (H3N2) infection in human, Kansas, USA, 2009.

Clinical Management of Pandemic 2009 Influenza A(H1N1) Infection

Triple-reassortant (tr) viruses of human, avian, and swine origin, including H1N1, H1N2, and H3N2 subtypes, emerged in North American swine herds in 1998 and have become predominant. While sporadic human infections with classical influenza A (H1N1) and with tr-swine influenza viruses have been reported, relatively few have been documented in occupationally exposed swine workers (SW). We conducted a 2-year (2002-2004) prospective cohort study of transmission of influenza viruses between pigs and SW from a single pork production company in Iowa. Respiratory samples were collected and tested for influenza viruses from SW and from pigs under their care through surveillance for influenza-like illnesses (ILI). Serial blood samples from study participants were tested by hemagglutination inhibition (HI) for antibody seroconversion against human and swine influenza viruses (SIV), and antibody seroprevalence was compared to age-matched urban Iowa blood donors. During the first year, 15 of 88 SW had ILI and were sampled; all were culture-negative for influenza. During the second year, 11 of 76 SW had ILI and were sampled; one was culture-positive for a human seasonal H3N2 virus. Among 20 swine herd ILI outbreaks sampled, influenza A virus was detected by rRT-PCR from 17 with 11 trH1N1 and five trH3N2 virus isolates cultured. During both years, HI geometric mean titers were significantly higher among SW compared to blood donor controls for three SIV: classical swine Sw/WI/238/97 (H1N1), tr Sw/IN/9K035/99 (H1N2), and trSw/IA/H02NJ56371/02 (H1N1)] (P < 0·0001). SW had serologic evidence for infection with both swine and human influenza viruses and were exposed to diverse influenza virus strains circulating in pigs. Influenza virus surveillance among pigs and SW should be encouraged to better understand cross-species transmission and diversity of influenza viruses at the human-swine interface.

Enhanced replication of swine influenza viruses in dexamethasone-treated juvenile and layer turkeys

Please cite this paper as: Ngo et al. (2012) Isolation of novel triple‐reassortant swine H3N2 influenza viruses possessing the hemagglutinin and neuraminidase genes of a seasonal influenza virus in Vietnam in 2010. Influenza and Other Respiratory Viruses 6(1), 6–10.Surveillance of swine influenza viruses (SIVs) in 31 pig farms in northern and southern parts of Vietnam was conducted. Six H3N2 influenza A viruses were isolated from a pig farm in southern Vietnam. They were novel genetic reassortants between a triple–reassortant SIV and a human seasonal H3N2 virus. Their hemagglutinin and neuraminidase genes were derived from a human virus circulating around 2004–2006 and the remaining genes from a triple‐reassortant SIV that originated in North America. This is the first report describing the isolation of a novel triple‐reassortant SIV in Vietnam.

BackgroundAmong swine, reassortment of influenza virus genes from birds, pigs, and humans could generate influenza viruses with pandemic potential. Humans with acute infection might also be a source of infection for swine production units. This article describes the study design and methods being used to assess influenza A transmission between swine workers and pigs. We hypothesize that transmission of swine influenza viruses to humans, transmission of human influenza viruses to swine, and reassortment of human and swine influenza A viruses is occurring. The project is part of a Team Grant; all Team Grant studies include active surveillance for influenza among Hutterite swine farmers in Alberta, Canada. This project also includes non-Hutterite swine farms that are experiencing swine respiratory illness.Methods/DesignNurses conduct active surveillance for influenza-like-illness (ILI), visiting participating communally owned and operated Hutterite swine farms twice weekly. Nasopharyngeal swabs and acute and convalescent sera are obtained from persons with any two such symptoms. Swabs are tested for influenza A and B by a real time RT-PCR (reverse transcriptase polymerase chain reaction) at the Alberta Provincial Laboratory for Public Health (ProvLab). Test-positive participants are advised that they have influenza. The occurrence of test-positive swine workers triggers sampling (swabbing, acute and convalescent serology) of the swine herd by veterinarians. Specimens obtained from swine are couriered to St. Jude Children's Research Hospital, Memphis, TN for testing. Veterinarians and herd owners are notified if animal specimens are test-positive for influenza. If swine ILI occurs, veterinarians obtain samples from the pigs; test-positives from the animals trigger nurses to obtain specimens (swabbing, acute and convalescent serology) from the swine workers. ProvLab cultures influenza virus from human specimens, freezes these cultures and human sera, and ships them to St. Jude where sera will be examined for antibodies to swine and human influenza virus strains or reassortants. Full length sequencing of all eight genes from the human and swine influenza isolates will be performed so that detailed comparisons can be performed between them.DiscussionThe declaration of pandemic influenza in June 2009, caused by a novel H1N1 virus that includes avian, swine and human genes, highlights the importance of investigations of human/swine influenza transmission.

The current epizootic of H5N1 highly pathogenic avian influenza (HPAI) in poultry is unprecedented in its virulence, extent and longevity, raising global concern that the virus could mutate into a form easily transmitted between humans and initiate an influenza pandemic. The ability to rapidly and accurately diagnose infections with novel influenza subtypes is crucial to minimizing morbidity and mortality in humans and reducing the potential for a pandemic. However, questions remain about how to ensure validity of the currently available diagnostics, optimize their availability and the potential offered by new technologies. To address these questions, during 19–20 February 2007, more than 40 scientists, clinicians, researchers and industry representatives from around the world came together for the first World Health Organization (WHO) Consultation on Diagnosis of H5N1 Avian Influenza Infections in Humans (summary available at http://www.who.int/csr/disease/avian_influenza/guidelines/diagnosis_consultation/en/index.html). The meeting was co-organized by the WHO Global Influenza Programme (GIP), the International Society for Influenza and other Respiratory Viruses (ISIRV) and the Foundation for Innovative New Diagnostics (FIND). This marked the first time public and private sectors met at length to discuss this important issue. An 'open forum' meeting style was adopted, and substantial time was allotted for discussion. Overall, the consultation addressed: The 'state of the art' for H5N1 diagnostics in humans. Considerations and gaps related to H5N1 diagnostic capacity. Collaborative ways forward and the roles of WHO, private industry and other stakeholders. This meeting summary will present the discussions and recommendations generally agreed by the consultation participants. Diagnostic tests (to identify influenza virus in clinical material, containing cells and secretions and tissues) are based either on growth of virus in culture or by direct detection of virus antigen or RNA. Virus may be amplified in embryonated chicken eggs or mammalian cell culture, and then subjected to further testing for identification. Serological techniques [e.g. haemagglutination inhibition (HI) or microneutralization (MN)] may also be used to identify the presence of antibody in the serum of exposed individuals, providing indirect evidence of infection. These basic techniques can be used for diagnosing infections both in humans and in animals. In general, antigenic or molecular screening is used to first identify influenza virus type (A or B). Then the specific subtype is identified based on either serological reactivity of two viral surface glycoproteins, haemagglutinin (HA) and neuraminidase (NA), or on molecular characterization of the genes coding for these two proteins. There are 16 recognized HA and nine recognized NA subtypes of influenza A viruses. Wild waterfowl are considered the natural reservoir for influenza A viruses, and all HA and NA subtypes of influenza A have been identified in birds. Currently, only two influenza A subtypes (H1N1 and H3N2) are circulating or appearing in humans, causing recurring human seasonal influenza epidemics. Since the start of the current H5N1 HPAI epizootic in 2003, the virus has caused disease in poultry and wild birds in at least 59 countries in Asia, Africa, and Europe (http://www.oie.int). Although to date H5N1 remains an avian virus, it can cross the species barrier, and human infections with the avian H5N1 virus have now been confirmed in 12 countries.† † http://www.who.int/csr/disease/avian_influenza/country/cases_table_2007_07_25/en/index.html In addition to global concern about disease and deaths in humans, there is also concern that the virus will mutate into a form easily transmitted between humans, initiating a pandemic. The ongoing exposure of humans in countries experiencing disease in animals and ensuing global pandemic concern have highlighted some gaps and challenges in human influenza diagnostics. Appropriate clinical management, including timely treatment of human H5N1 cases‡ ‡ http://www.who.int/medicines/publications/WHO_PSM_PAR_2006.6.pdf , as well as plans for containing an emerging influenza pandemic,§ § http://www.who.int/csr/disease/avian_influenza/guidelines/draftprotocol/en/index.html rely on the ability to rapidly and accurately diagnose the virus in humans. Ensuring that effective influenza diagnostic systems are in place globally could be extremely cost effective. For example, it has been shown that although laboratory diagnosis represents a small percentage of medical centre costs, it leverages 60–70% of all critical decisions, e.g. admission, discharge and drug therapy.1Diagnosis of H5N1 in humans is not yet achievable in the vast majority of diagnostic laboratories. One challenge to rapid and accurate diagnosis is the continual evolution of influenza viruses.2 The eight RNA gene segments of influenza A viruses mutate at different rates.3 Specifically, the HA and NA genes, on which diagnostics depend, have high mutation rates compared to the other genes. This rapid evolution in the H5N1 viruses isolated since 1997 has resulted in the emergence of genetically and antigenically distinct lineages (http://www.WHOweblink.org). The circulating H5N1 viruses can currently be grouped into many different clades with four clades including viruses that have infected humans in the following countries:4 Clade 1 Thailand, Vietnam, Cambodia, China Clade 2.1 Indonesia Clade 2.2 China, Iraq, Azerbaijan, Turkey, Egypt, Nigeria, Djibouti Clade 2.3 China, Laos, Vietnam A second major challenge to global diagnostic capability is the availability of healthcare infrastructure to rapidly diagnose H5N1 infection at the initial point of care (POC), as the virus is circulating in many regions that lack existing diagnostic capacity, even for seasonal influenza. In practice, diagnosis of viral infections is conducted in several different environments, each having specific features, and therefore having somewhat different test requirements (Table 1). The third challenge is the uncertainty about the demand for tests for emerging influenza strains over the next months and years. Because the course of the H5N1 epizootic in animals and associated infections in humans cannot be predicted, it is possible that demand will decrease if the epizootic begins to be controlled in animals. It is also possible that demand will increase rapidly if there is suspected human-to-human transmission and the pandemic phase increases. Therefore, questions of stockpiling, reagent/kit shelf life, production times, etc. must be considered. The actual technical 'know how' for influenza diagnosis is fairly advanced, though this has not yet translated into significant innovation in rapid detection in field settings. Improvements are continually being made in both antigenic and molecular techniques for antigen and antibody detection, including development of increasingly simple-to-use tests (e.g. dipstick tests). Simpler techniques are required for routine diagnostic screening and sero-epidemiological studies in the field. Despite technological advances, however, the accuracy of H5N1 diagnoses relies heavily on the quality of the specimens collected and their preparation. If samples are not collected from patients early in the course of their infection and/or from sites where the viral load is high, or if samples are not handled, stored, and transported appropriately, false-negative tests may result irrespective of the validity of the test used. Approaches to collecting, preserving and shipping specimen for the diagnosis of avian influenza A (H5N1) have been summarized in a WHO document previously and are available at http://www.who.int/csr/resources/publications/surveillance/WHO_CDS_EPR_ARO_2006_1/en/. The basic diagnostic approaches, including benefits and constraints, are described below. Virus culture in eggs is traditionally regarded as the gold standard for amplifying and detecting avian influenza viruses. Cell culture can also be used for amplification with several lines (e.g. primary monkey kidney, MDCK, HeLa, MRC-5 or LLC-MK2) available, using tube culture, shell vial or multi-well plates. The cytopathic effect in cell culture to identify positives is not always distinctive; sensitivity of cell lines can vary for different strains, and there can be variation in the relative diagnostic yield from different techniques. Once cultured, virus can be easily detected and identified using techniques such as haemadsorption, antigen detection by immunofluorescence, other immunossays or haemagglutination (http://www.diagnosticdocweblink.org). Increasingly, polymerase chain reaction (PCR) is being used directly on original clinical samples, eliminating this virus isolation step for the purpose of diagnosis (see below). However, virus isolation as part of the diagnostic approach has the additional benefit of providing strains for further characterization, and vaccine development. The need for BSL-3 containment (BSL-3 enhanced or BSL-4 in some countries) for isolation and/or amplification of the HPAI H5N1 viruses constrains the use of virus isolation for diagnosis of this virus in many laboratories. The MN assay remains the gold standard for serological diagnosis of H5N1 infection in humans.4 Other methods include HI with use of horse red blood cells, complement fixation, single-radial haemolysis and enzyme immuno assay. Conventional HI tests that use turkey or chicken RBC have poor sensitivity for the detection of antibodies to avian influenza viruses including H5N1. However, the HI assay using horse red blood cells may be a suitable alternative for sero-diagnosis of some avian viruses (e.g. H5N1) but this may not apply to all avian influenza subtypes, highlighting the fact that significant strain/subtype differences exist. The international body of knowledge for serological diagnosis of H5 subtype infections is growing but information on other subtypes (e.g. H7) is limited. Although the methods for serological diagnosis differ in various laboratories, WHO does provide a set of standard criteria for serological diagnosis of human infection of avian influenza infection, i.e. a person meeting clinical definition of H5N1 case and one of the following:¶ ¶ http://www.who.int/csr/disease/avian_influenza/guidelines/case_definition2006_08_29/en/index.html Serological confirmation with appropriately timed paired sera. Greater than fourfold rise in neutralization antibody titre for H5N1. An MN antibody titre for H5N1 ≥1:80. A positive result using a different serological assay (e.g. A horse RBC HI titre of ≥1:160 or greater or H5-specific western blot positive result). There can be considerable variability in results on consecutive serological testing. Thus, negative and positive controls must always be included and samples/studies with low titre cut-off points should be interpreted with caution. Nonspecific reactivity of samples can be a problem. Modification techniques (e.g. serum adsorption) may be necessary to remove cross-reactive antibodies, especially when human infection with a novel avian subtype (such as H5) is reported. Nonspecific cross reactivity in patients 60–70 years of age can be seen when using the MN test.5 It remains unclear whether the cross-reactivity might be associated with some degree of protection in humans.6 Novel serological assays based on the use of engineered viruses with H5 antigen may allow 'neutralization' of H5N1 viruses to be carried out in a BSL-2 setting.7 As antibody response to H5N1 virus appears only in the second week of illness, serological tests cannot be used to detect early stages of influenza infection. Current serological tests are therefore most useful to identify mild or asymptomatic infections and epidemiologically assess populations at risk of exposure, such as family members and contacts of H5N1 case-patients, healthcare workers or co-workers and individuals exposed to infected domestic or wild birds. However, there is not much sero-epidemiological information being systematically collected globally. Follow-up investigations on specific outbreaks have yielded some data8, 9 but the extent of human exposure to H5N1 remains largely unknown. Immunofluorescence assays (both direct and indirect) can be used for detection of H5N1 antigen in samples, but rely heavily on specimen quality. While rapid, these methods are also dependent on the quality of fluorescence reagents and the expertise of the person interpreting the results of the tests and have inherently low sensitivity. Enzyme immunoassays in a micro-plate format are not widely used for human influenza diagnostics but the immuno-assay principle has been adapted for rapid antigen detection (rapid diagnostic tests) by flow-through or lateral flow devices. Sensitivity and specificity of antigenic tests depend not only on the test technique, but also on factors like type of specimen analysed, quality of specimen and timing of specimen collection (related to viral shedding).10 Based on published data, sensitivities for detection of human influenza H1N1 or H3N2 in rapid diagnostic tests are approximately 70–75% while specificities are approximately 90–99%. It should be noted that sensitivity of such methods for direct detection of H5N1 has been disappointing so far. The analytical sensitivity of currently available antigen detection test kits for influenza A remains too low for reliable use as POC tests for direct detection of H5N1 virus in clinical specimens. But if the sensitivity of such methods can be enhanced, they may become useful for H5N1 rapid testing.11 The use of molecular techniques to identify specific gene sequences provides a sensitive method for diagnosis. Furthermore, their use can potentially reveal the genetic sequence of the virus which is useful for molecular epidemiology and provides other important characteristics of the virus, including antiviral resistance status, occurrence of genetic reassortment or presence of key virulence mutations. While some of this information can be obtained by direct sequencing of PCR-amplified viral cDNA, more detailed molecular analysis typically requires prior virus amplification by culture. PCR is used widely now, with thermocyclers and other requisite equipment available in many national laboratories throughout affected regions although maintenance of the assays requires regular update of generic information. The multiple test steps (extraction, amplification, detection) and reagent preparation are highly sensitive to minor changes and requires experienced personal working within good quality systems. In particular, the amplification reaction of viral nucleic acids makes it susceptible to cross-contamination, unless stringent measures to avoid such contamination are in place.12 'Chip technology', which includes miniaturized approaches to genetic sequence detection may also allow simple, automated, rapid and economical PCR testing on a large scale, but automated systems are still expensive, and availability of a POC chip platform is at least 4 years away. Numerous sophisticated chip approaches to detection are available but all ultimately depend upon binding to specified virus sequences. As the viral mutation rate is high, it is important for all these approaches that constant surveillance of viral genetic sequence variations occurs, allowing adjustments to primers and probes. PCR can also be performed in a multiplex format for a panel of respiratory pathogens that is relevant to the differential diagnosis of AI and viral pneumonia (e.g. influenza B, parainfluenza 1, 2 and 3, respiratory syncytial virus, metapneumovirus, adenovirus, coronaviruses, mycoplasma and chlamydiae). A clinically and/or epidemiologically credible alternative diagnosis is useful in excluding AI. Closed tube real-time (RT) PCR systems that utilize fluorescent detectors are now widely available in a variety of formats including portable ones easily used in the field or for POC analysis. These show promise, but remain expensive for provincial or local laboratories and even though off the shelf reagents are available for detection of H5N1 strains, training of personnel and suitable laboratory environments are still crucial. Other molecular strategies are under development for rapid identification of influenza infections. For example, microarray and proteomic analysis of peripheral blood leucocytes or serum, respectively, may, in future, identify host response markers (e.g. gene response profiles, acute phase proteins, cytokines or other immune regulators) that may provide useful diagnostic signatures characteristic of groups of aetiological agents. During the consultation, a myriad of technical, political, economic and cultural issues were discussed. The following three general points emerged as being key to optimizing H5N1 diagnostics globally. In general, current technologies are adequate for the detection and characterization of diagnostic samples at the reference laboratory level, though advances in speed and miniaturization are occurring. There is however an acute need for field and POC tests that are relatively simple, sensitive and specific enough for use at referral hospitals and primary healthcare facilities. Such tests need to be to detect and between currently circulating strains of both avian influenza and seasonal influenza and enough to genetic changes in the For POC screening the sensitivity should be as high as possible to and tests should be The sensitivity of currently used rapid tests for H5N1 disease is from in the 1997 to in the and sensitivity does not always clinical sensitivity of diagnostic However, the poor clinical sensitivity of current POC tests for detecting H5N1 is not to a poor sensitivity for detecting H5N1 virus to human influenza but the poor analytical sensitivity for detecting influenza viral antigen in Furthermore, the of test also on the of the disease for test sensitivity and the positive for test will be and negative will be when influenza is rapid POC diagnostic with high sensitivity tests must be where it is for and shipping specimens to laboratories in the This may new techniques to be that into the challenges at many POC in affected In general, the ability to rapidly and accurately including human influenza has in though issues remain that the of many techniques. Appropriate collection may be including viral collection and and The specimens for virus detection have been summarized in the relevant WHO load in different clinical specimens in patients with H5N1 disease that are to and that respiratory specimens (e.g. are to be than respiratory specimens. There are with of specimens as well as A chain may be in and of and systems may not have been previously and the may not be may to to lack of and uncertainty of are to expensive when available, and may with a shelf and kits may or protection from which cannot be and may be of high (e.g. become or when may when have an even more shelf for may be In there is specific national to the reagents and There may be a lack of experienced lack of for training and a lack of training There may not be of the various assays and their use and (e.g. including of the different rapid detection While these may be and other emerging disease and public the need for diagnostic for influenza. of equipment is of an than is the lack of infrastructure to including for of the equipment and technical as well as international and may be in some and may not be possible in some laboratories, risk of of samples and risk of human human protection equipment may not be available, or may be used to training or (e.g. of protection level, of to and other equipment may be for the of new tests and reference strains for their quality are on a global level, from industry to assays and diagnostic As an international standard for H5N1 diagnostic test though has not yet been a relatively influenza gene (such as the infections with influenza A subtype can still be identified even in the of ongoing virus However, for identification of virus the reagents in diagnostic tests on either molecular sequences or must be continually to the currently circulating false-negative results can be and kits must therefore be easily to changes to allow detection of emerged strains and reagents should be continually identified by and be available WHO Influenza testing for both genes (e.g. to detect all influenza A strains with subtype specific tests the haemagglutinin of human and avian subtypes, one can avoid false-negative results of variations in the viral However, timely availability of viral and genetic sequence is a major to the and of reference reagents and Thus, ongoing surveillance of H5N1 viruses in animals and humans and global of are ultimately crucial to diagnostic test development and the validity of tests used. The Influenza influenza in countries and a of and laboratories by Currently, the H5N1 controls H5 H5 RNA and H5N1 has that one set and is not suitable for all and some diagnostic have specific Therefore, within Europe it is that different of reference reagents should be available, and primers and must be on each Currently, the WHO for Influenza at the for and in the provides domestic for its PCR influenza including of assays to laboratories and to other public laboratories, and of positive H5N1 to public laboratories in the at The and reagents are also available to international public laboratories. for human diagnostic test differ countries and from and to also vary different countries and some countries more than a to new diagnostic techniques. countries and/or for their although these may be time and expensive to especially for new technologies. International of requirements for could countries by providing both and industry a set of recognized should be based on risk and to public and be and International for including can be by following studies different laboratories. The of WHO International for avian influenza diagnosis should be to and subtype it may not be possible to international for H5N1 reagents and the of may need to be Serological test results are highly between laboratories. In to be to H5N1 results from different assays or laboratories, assays an standard may be more than an response can be and variation could be compared and Currently, the WHO is with including and on a virus neutralization to between laboratories H5 from show that the laboratories using and HI assays to test for H3N2 of the laboratories could not than results in In a of a quality for influenza virus detection and was by for Diagnostics in with the for Diagnostics of and some national reference laboratories. from within various sectors (e.g. reference laboratories, laboratories, and public were from that positives were Other challenges remain in detecting and of influenza virus, in influenza and influenza quality remain crucial to and document adequate and should be An important is the of positive H5N1 clinical samples for test from other for and should be and the various of samples, use of considered. International should be As the of avian influenza infections in humans it is important to that H5N1 remains a disease of animals. Although the for influenza testing are somewhat the and of diagnostic test techniques are for and human In the currently circulating strains in animals are still that will most as the virus has not yet adapted to humans. Therefore, the of of tests and as well as technical personnel in human and diagnostic laboratories should be As diagnosis of AI in animals is made on specimens where viral load is high and a only requires a animals from a to be confirmed as AI for relevant the sensitivity of POC tests is stringent that it is for diagnosis of human infection. surveillance and is to the risk factors for human infection with ongoing of the public sectors with the sectors and studies at the (e.g. birds in where H5N1 has poultry workers and poultry at should be national should not on laboratory but should in the collection of the surveillance in to strategies of and to the and of WHO and the public in to direct its and development for influenza diagnostics in the of the uncertainty of for H5 and influenza diagnostics. is considerable time and in new and diagnostic approaches and technologies for from use of to of methods to large or multiplex assay The public benefits when industry is in to ongoing and can by the required diagnostic analytical sensitivity and other clinical It should also be recognized that for of diagnostic clinical specimens of viral load to be in clinical are important in test and may in fact be to clinical specimens from patients which are a and and may be with multiple specimen should be to from such clinical specimens for test under the WHO International Health will be to rapid detection of human infections with influenza viruses in the now influenza reference laboratories, with of culture and influenza could diagnostic testing where national is The WHO Global Influenza Programme and its of Influenza and can a in this in by providing training and technical and global public benefit from of the following the of local and the for influenza testing at POC and in referral hospitals in regions and at risk development and of rapid, sensitive and specific POC screening tests for H5N1 infections in humans. collection of virus from animals and humans and their to reference laboratories in to be to currently circulating influenza strains and update tests the of reference laboratories in providing technical kits and reference should be between public and and available international of reagents and clinical are to from such specimens for test a global of avian influenza viruses in with development of the international of the of international for H5N1 diagnostic criteria and for all for new and including use of samples requirements a WHO working to the next steps in of reagents global of avian influenza viruses and for of H5N1 diagnostic tests

Despite extensive planning for the next influenza pandemic in humans, nature has once again confounded the influenza experts. The emergence and development of an H1N1 pandemic strain while an H1N1 virus was still circulating in humans is an unprecedented event. Here, we examine the emergence of H1N1 influenza viruses in the USA, Europe, and Asia from the natural aquatic bird reservoir through intermediate hosts including pigs and turkeys to humans. There were some remarkable parallel evolutionary developments in the swine influenza viruses in the Americas and in Eurasia. Classical swine influenza virus in the USA emerged either before or immediately after the Spanish influenza virus emerged in humans in 1918. Over the next 50 plus years this swine influenza virus became increasingly attenuated in pigs but occasionally transmitted to humans causing mild clinical infection but did not consistently spread human to human. The remarkable parallel evolution was the introduction of avian influenza virus genes independently in swine influenza viruses in Europe and the USA, with almost simultaneous acquisition of genes from seasonal human influenza. Influenza in pigs in both Eurasia and America became more aggressive necessitating the production of vaccines, and the incidence of transmission of clinical influenza to humans increased. Eventually the different triple reassortants with gene segments from avian, swine, and human influenza viruses in pigs in Europe and America met and mated and developed into the 2009 pandemic H1N1 influenza that is highly transmissible in people, pigs, and turkeys. Whether this occurred in Mexico or in Asia is currently unknown. The failure of the experts was to not recognize the importance of pigs in the evolution and host range transmission of influenza viruses with pandemic potential.

Genetic correlation between current circulating H1N1 swine and human influenza viruses

no comparative uptake data are available to supplement our evaluation of the intervention.Information relating to the outbreak was placed in 2 Orthodox Jewish newspapers and targeted information for families (in English, Yiddish, and Hebrew) has been disseminated.Finally, all 25 HPTs were alerted to this outbreak and the national Public Health England database (HPZone) has been enhanced to capture notifications from Orthodox Jewish communities.This ongoing outbreak highlights continued health risks in communities with low vaccination coverage.The outbreak has been largely contained within London's Orthodox Jewish communities, with limited spread outside of the city and to just 1 local non-Orthodox Jewish child.Given the mobility of members, the risk for transmission outside of London is relatively high.The outbreak underscores the need for ongoing evidence-based and culturally appropriate health interventions that seek to improve vaccination coverage.

Novel triple-reassortant H1N1 swine influenza viruses in pigs in Tianjin, Northern China

Replication of swine and human influenza viruses in juvenile and layer turkey hens

前言：豬對於禽流感與人流感皆同樣具有敏感性，這使得豬隻在流感病毒八段基因的重組上扮演重要角色。因抗原性的顯著改變，重組出來的病毒有可能會造成全球性的大流行，例如2009年的新流感H1N1。有研究發現，已經出現帶有2009年新流感H1N1基因的新重組豬流感病毒H3N2，且人類感染豬流感病例也有增加的情形，因此，對於豬流感可能造成的威脅，評估人們對它的抗體反應以及疫苗保護效力是其中很重要的一點。此外，本篇亦會評估2009年針對新流感所採取的疫苗政策以及對於後續疫苗效果的影響，作為以後的參考。本篇研究利用血球凝集抑制試驗來測試抗體分布情形，包括三大主題：(1)台灣地區不同年齡層血清對於不同年代分離的A型豬流感 (H3N2)交叉反應抗體之縱貫性研究 (2) 2009年爆發新型流感疫情後不同疫苗施打狀況對新型流感抗體持續力之影響 (3) 2010年疫苗株與前一年不同對於學童抗體免疫效果之評估。 結果：(1) 研究所用之豬流感病毒包括A/Swine/Taiwan ex USA/28-9/2010 (HA與2005人流感相似)、 A/Swine/Taichung/50-1/2004、A/Swine/Yunlin/113-3/2010與A/Swine/Obihiro/10/1985 (後面三株HA與1980年代的人流感相似)。人類血清則是於2008-2010年期間收集，且依據前述病毒的HA相似性分成三個年齡層：1980年前出生、1981-1999年出生與2000年後出生。結果發現，針對台灣本土的病毒株，GMT與血清保護率有隨著年齡層提高而增加的趨勢 (三個年齡層的分佈分別為GMT: 5, 5.485, 10.315; seroprotection rate: 0, 3.14, 23.59 %)。然而成年人的抗體卻有逐年減少的情形 (GMT: 14.42 and 5.8; seroprotection rate: 38.83 and 2.68 %, from 2008 to 2010, respectively)。 (2) 依據2009年疫苗施打記錄將國小學童分成兩個族群：只有打2009新流感疫苗的以及2009新流感和季節流感疫苗都有打的人，年齡層則分成一到三年級 (打兩劑新流感疫苗)和四到六年級 (只打一劑新流感疫苗)。結果發現，只有打新流感疫苗的高年級到了2010疫苗施打前時，血清保護率只剩下64.71 %，此時低年級尚有82.76的保護率。兩族群相比，則在2010疫苗施打前的時間點，高年級group1 (64.71 %)的血清保護率顯著的低於group 2 (91.30 %)。 (3) 根據2009與2010年疫苗記錄將國小學童分成四個族群：連續兩年都有打疫苗、只有2010有打、只有2009有打以及兩年都沒打的人。結果發現，對於連續兩年疫苗株都一樣的H1N1，重複施打者的GMT與血清保護率顯著較高，不過相同情形的B型流感則沒有顯著差異。此外對於疫苗株有變的H3N2，重複施打者的抗體反應反而比較低。 結論：本篇研究發現，長期下來不論小孩或成人對於豬流感病毒皆不具有足夠的交叉保護抗體，製造針對新重組病毒的疫苗是有其必要性存在。此外，對於國小學童來說，重複施打相同疫苗可促進抗體產生，若是不同疫苗則需要小心評估。

Swine influenza is a highly contagious respiratory viral infection of pigs that has become enzootic in areas densely populated with pigs. Like other influenza A viruses, swine influenza virus (SIV) is genetically unstable and able to accumulate antigenic drifts and/or antigenic shifts. The pig is susceptible to both avian and human influenza viruses and can serve as an intermediate host in influenza virus ecology. Zoonotic agents may emerge in pigs following the modification of an established swine strain, adaptation of a strain of avian origin to the mammalian host, or reassortment between human and avian influenza viruses. Three different subtypes, H1N1, H3N2 and H1N2, are at present circulating in Europe. They differ from those found in North America and Asia and various lineages can be distinguished within each subtype. To date, European SIVs have not produced a global outbreak of influenza in humans but sporadic cases of SIV infection have been reported. This review presents a historical record of the genetic and antigenic evolution of SIVs in Europe. Our present understanding of the transmission of European SIVs from pigs to other animal species and to humans, together with the factors that limit inter-species transmission, is described.

Influenza A virus is characterized by a genome composed of eight single-stranded, negative sense RNA segments, which allow for reassortment between different strains when they co-infect the same host cell. Reassortment is an important driving force for the evolution of influenza viruses. The ability of reassortment allows influenza virus to endlessly reinvent itself and pose a constant threat to the health of humans and other animals. Of the four human influenza pandemics since the beginning of the last century, three of them were caused by reassortant viruses bearing genes of avian, human or swine influenza virus origin. In the past decade, great efforts have been made to understand the transmissibility of influenza viruses. The use of reverse genetics technology has made it substantially easier to generate reassortant viruses and evaluate the contribution of individual virus gene on virus transmissibility in animal models such as ferrets and guinea pigs. H5, H7, and H9 avian influenza viruses represent the top three subtypes that are candidates to cause the next human influenza pandemic. Many studies have been conducted to determine whether the transmission of these avian influenza viruses could be enhanced by acquisition of gene segments from human influenza viruses. Moreover, the 2009 pdmH1N1 viruses and the triple reassortant swine influenza viruses were extensively studied to identify the gene segments that contribute to their transmissibility. These studies have greatly deepened our understanding of the transmissibility of reassortant influenza viruses, which, in turn, has improved our ability to be prepared for reassortant influenza virus with enhanced transmissibility and pandemic potential.

Avian Influenza Virus Infections in Humans