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Antigenic and genetic characteristics of zoonotic influenza viruses and development of candidate vaccine viruses for pandemic preparedness, September 2013 (WHO, extract)
[Source: World Health Organization, full PDF document: (LINK). Excerpts.]
Weekly epidemiological record, Relev? ?pid?miologique hebdomadaire, 18 october 2013, No. 42, 2013, 88, 449?464, http://www.who.int/wer
Antigenic and genetic characteristics of zoonotic influenza viruses and development of candidate vaccine viruses for pandemic preparedness, September 2013
The development of representative candidate influenza vaccine viruses, coordinated by WHO, remains an essential component of the overall global strategy for pandemic preparedness. Comparisons of the candidate vaccine viruses with respect to antigenicity and their relationship to newly emerging viruses are ongoing and will be reported periodically by WHO.
(1) Influenza A(H5N1)
Since their re-emergence in 2003, highly pathogenic avian influenza A(H5N1) viruses have become enzootic in some countries and continue to cause outbreaks in poultry as well as sporadic human infections. The A(H5N1) viruses have diversified both genetically and antigenically leading to the need for multiple candidate vaccine viruses for pandemic preparedness purposes. This summary provides updates on the characterization of A(H5N1) viruses isolated from birds and humans, and the current status of the development of influenza A(H5N1) candidate vaccine viruses.
Influenza A(H5N1) activity: 19 February ? 23 September 2013
A(H5N1) viruses have been detected in birds in Africa and Asia. Human infections have been reported to the WHO by Cambodia, Egypt, Indonesia, and Viet Nam, countries in which infections have been detected in birds (Table 1).
Antigenic and genetic characteristics of A(H5N1) viruses
The nomenclature for phylogenetic relationships among the haemagglutinin (HA) genes of A(H5N1) viruses is defined in consultation with representatives of the WHO, the Food and Agriculture Organization of the United Nations (FAO), the World Organisation for Animal Health (OIE) and academic institutions. The updated nomenclature report can be found on WHO web site.(1)
Viruses circulating and characterized from 19 February to 23 September 2013 belonged to the following clades.
Clade 1.1 viruses were detected in poultry and humans in Cambodia and Viet Nam. Genetic characterization of the HA genes showed that these viruses were closely related to viruses detected previously in these countries (Figure 1). Some recent clade 1.1 viruses had reduced haemagglutination inhibition (HI) titres to post-infection ferret antisera raised against A/Viet Nam/1203/2004 and/or A/Cambodia/R0405050/2007 from which candidate vaccine viruses have been produced. Conversely, these viruses reacted well with post-infection ferret antisera raised against recent viruses isolated in Cambodia (Table 2). A new A/Cambodia/W0526301/2012-like candidate vaccine virus is proposed.
Clade 2.1.3.2 viruses continue to circulate in Indonesia. The HA gene sequence of a 2013 human virus was very similar to that of the candidate vaccine virus A/Indonesia/NIHRD11771/2011. No antigenic information is available.
Clade 2.2.1 viruses, similar to clade 2.2.1 viruses detected in previous years, were detected in poultry and humans in Egypt. These viruses reacted well with postinfection ferret antisera raised against available candidate vaccine viruses produced from A/Egypt/N03072/2010 and/or A/Egypt/2321-NAMRU3/2007.
Clade 2.3.2.1 viruses fall into 3 HA genetic groups as follows.
A/barn swallow/Hong Kong/D10-1161/2010-like viruses were detected in birds in China and Viet Nam but in reduced numbers compared to recent reporting periods. These viruses were genetically similar to viruses detected previously.
A/Hubei/1/2010-like viruses were detected in birds and/ or environmental samples from Bangladesh, China, India, Nepal, and Viet Nam (Figure 2). While some viruses reacted well with post-infection ferret antisera raised against the available candidate vaccine virus produced from A/Hubei/1/2010, others did not (Table 3). Due to these observations and the widespread distribution of these viruses, a new A/duck/Bangladesh/19097/2013-like candidate vaccine virus is proposed.
A/Hong Kong/6841/2010-like viruses were detected in China, Democratic People?s Republic of Korea, Indonesia (detected in birds illegally imported into Europe), and Viet Nam. Antigenically (Table 4) and genetically (Figure 3) some of these viruses have diverged from available candidate vaccine viruses, hence a new A/duck/Viet Nam/1584/2012-like candidate vaccine virus is proposed.
Clade 2.3.4.2 viruses were isolated from birds and environmental samples in China. The HA genes of these viruses were genetically similar to those of viruses detected previously. Antigenic characterization of these viruses is pending.
Clade 7.2 viruses were detected in China and Viet Nam. Genetically these viruses were similar to viruses characterized previously. These viruses had reduced reactivity to post-infection ferret antisera raised against available candidate vaccine viruses and further analyses are proposed to determine if production of additional candidates is needed.
Influenza A(H5N1) candidate vaccine viruses
Based on the available antigenic, genetic and epidemiologic data, A/duck/Bangladesh/19097/2013-like (clade 2.3.2.1), A/duck/Viet Nam/NCVD-1584/2012-like (clade 2.3.2.1) and A/Cambodia/W0526301/2012-like (clade 1.1) candidate vaccine viruses are proposed. The available and proposed candidate A(H5N1) vaccine viruses are listed in Table 5. On the basis of geographic spread, epidemiology and antigenic and genetic properties of A(H5N1) viruses in particular locations, national authorities may consider the use of one or more of these candidate vaccine viruses for pilot lot vaccine production, clinical trials and other pandemic preparedness purposes.
As the viruses continue to evolve, new A(H5N1) candidate vaccine viruses will be developed and announced as they become available. Institutions that wish to receive these candidate vaccine viruses should contact WHO at gisrs-whohq@who.int or the institutions listed in announcements published on the WHO website.(2)
(2) Influenza A(H9N2)
Influenza A(H9N2) viruses are enzootic in poultry populations in parts of Africa, Asia and the Middle East. The majority of viruses that have been sequenced belong to the G1, chicken/Beijing (Y280/G9), or Eurasian clades. Since 1998, when the first human infection was detected, the isolation of A(H9N2) viruses from humans and swine has been reported infrequently. In all human cases the associated disease symptoms have been mild and there has been no evidence of human-tohuman transmission.
Influenza A(H9N2) activity from 19 February to 23 September 2013
No human cases of A(H9N2) infection have been reported in this period. A(H9N2) viruses continue to be isolated from birds in many regions of the world.
Influenza A(H9N2) candidate vaccine viruses
Based on the current antigenic, genetic and epidemiologic data, no new A(H9N2) candidate vaccine viruses are proposed. The available A(H9N2) candidate vaccine viruses are listed in Table 6. Institutions that wish to receive candidate vaccine viruses should contact WHO at gisrs-whohq@who.int or the institutions listed in announcements published on the WHO website.(2)
(3) Influenza A(H7)
Influenza A(H7) viruses have been detected in poultry populations worldwide with the associated disease ranging from mild to severe. Occasionally, during outbreaks in poultry, human cases have been detected in those with direct poultry exposure. These infections often cause conjunctivitis or mild influenza-likeillness(3), (4) but some H7 infections, notably A(H7N9),(5) can cause severe respiratory disease.
Influenza A(H7N9) activity from February to 23 September 2013
The first instance of A(H7N9) infecting humans was reported to WHO on 31 March 2013. There were 135 human cases including 44 deaths. Geographic distribution of these human cases (and genetically related avian and/ or environmental samples) has been restricted to China. HA gene sequence and HI test comparison of A(H7N9) viruses isolated from humans and poultry suggest limited genetic and antigenic diversity among this group of viruses (Table 7 and Figure 4).
Influenza A(H7N9) candidate vaccine viruses
Based on the current epidemiologic data, A(H7N9) candidate vaccine viruses have been developed. Available A(H7N9) candidate vaccine viruses are shown in Table 8. Institutions that wish to receive candidate vaccine viruses should contact WHO at gisrs-whohq@who.int or the institutions listed in announcements published on the WHO website.(2)
Influenza A(H7N3) activity from 19 February to 23 September 2013
Highly pathogenic A(H7N3) viruses continue to circulate in poultry in Mexico. No human cases have been reported during this period.
Influenza A(H7N7) activity from 19 February to 23 September 2013
Since 14 August 2013 there have been 6 outbreaks of highly pathogenic avian influenza A(H7N7) in poultry in Italy. Three cases of A(H7N7) conjunctivitis were documented in personnel involved in culling operations with one case developing influenza-like illness. All individuals recovered without treatment. Genetically, the A(H7N7) viruses were similar to low pathogenic viruses circulating in wild birds in Europe and those causing sporadic and limited outbreaks in poultry in Central and Northern Europe (Figure 4). Antigenically, the A(H7N7) virus reacted well to post-infection ferret antisera raised against the candidate vaccine viruses A/turkey/Virginia/4529/2002 (H7N2) IBCDC-5 and A/mallard/Netherlands/12/2000 (H7N7) IBCDC-1.
Influenza A(H7) candidate vaccine viruses
Available A(H7) candidate vaccine viruses are shown in Table 9 additional to those available for A(H7N9) described in Table 8. Based on current data, no new A(H7N3) or A(H7N7) candidate vaccine viruses are proposed. Institutions that wish to receive candidate vaccine viruses should contact WHO at gisrs-whohq@who.int or the institutions listed in announcements published on the WHO website.(2)
(4) Influenza A(H3N2) variant (v)(6)
Influenza A(H3N2) viruses are enzootic in swine populations in most regions of the world. Depending on geographic location, the genetic and antigenic characteristics of these viruses differ. Human infections with swine A(H3N2) viruses have been documented in Asia, Europe and North America.(7)
Influenza A(H3N2)v activity from 19 February to 23 September 2013
Eighteen human cases of A(H3N2)v infection were reported in the United States (USA) during this reporting period.(8) These viruses were genetically and antigenically similar to previously characterized A(H3N2)v viruses. All cases had known exposure to swine at agricultural fairs. Similar viruses continue to be isolated from pigs in the USA.
Influenza A(H3N2)v candidate vaccine viruses
Based on the current antigenic, genetic and epidemiologic data, no new A(H3N2)v candidate vaccine viruses are proposed. Available candidate vaccine viruses are shown in Table 10. Institutions that wish to receive candidate vaccine viruses should contact WHO at gisrswhohq@who.int or Centers for Disease Control and Prevention, USA.
(5) Influenza A(H1N1)v
Influenza A(H1N1) viruses circulate in swine populations in many regions of the world. Depending on geographic location, the genetic characteristics of these viruses differ. Human infections with swine A(H1) viruses have been documented for many years.(9) Two human infections with A(H1N1)v viruses have been detected in the USA during the reporting period. These viruses are genetically similar to viruses circulating in swine in the region and to A(H1N1)v viruses detected in previous years.
Influenza A(H1N1)v candidate vaccine viruses
Based on a risk assessment of the antigenic and genetic characteristics of the A(H1N1)v viruses, candidate vaccine viruses are not proposed at this time.
(6) Influenza A(H6N1)
A human infection with A(H6N1) virus was detected in Taiwan, China in May.(10) No human A(H6N1) infections had been detected previously. The virus was genetically similar to viruses isolated from chickens in Taiwan, China but different from A(H6N1) viruses circulating in poultry in other regions of Asia.
Influenza A(H6N1) candidate vaccine viruses
Based on a risk assessment, no candidate vaccine viruses have been proposed at this time.
(...)
________
(1) Updated unified nomenclature system for the highly pathogenic H5N1 avian influenza viruses. Geneva, World Health Organization, 2011 (http://www.who.int/influenza/gisrs_laboratory/h5n1_nomenclature/en/, accessed September 2013).
(2) Candidate vaccine viruses and potency testing reagents for influenza A(H5N1). Available at http://www.who.int/influenza/vaccines/virus/en/, accessed September 2013.
(3) Tweed, SA et al. Human illness from avian influenza H7N3, British Columbia. Emerging Infectious Diseases, 2004, 10(12): 2196?2199.
(4) de Jong MC et al. Intra- and interspecies transmission of H7N7 highly pathogenic avian influenza virus during the avian influenza epidemic in the Netherlands in 2003. Revue scientifique et technique de l?Office international des ?pizooties (OIE), 2009, 28(1):333?340.
(5) Avian influenza A(H7N9) virus. Available at http://www.who.int/influenza/human_animal_interface/influenza_h7n9/en/, accessed September 2013.
(6) Standardization of terminology for the variant A(H3N2) virus recently infecting humans. Available at http://www.who.int/influenza/gisrs_laboratory/terminology_ah3n2v/en/index.html/, accessed September 2013.
(7) Myers KP et al. Cases of swine influenza in humans: a review of the literature. Clinical Infectious Diseases, 2007, 44:1084?1088.
(8) Situation summary on influenza A (H3N2) variant viruses (H3N2v). Available at http://www.cdc.gov/flu/swineflu/h3n2v-situation.htm, accessed September 2013.
(9) Shu B et al. Genetic analysis and antigenic characterization of swine origin influenza viruses isolated from humans in the United States, 1990?2010. Virology, 2012, 422:151.
(10) Yuan, J. et al. Origin and molecular characteristics of a novel 2013 avian influenza A(H6N1) virus causing human infection in Taiwan, 2013. Clinical Infectious Diseases, 2013 [Epub ahead of print].
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Weekly epidemiological record, Relev? ?pid?miologique hebdomadaire, 18 october 2013, No. 42, 2013, 88, 449?464, http://www.who.int/wer
Antigenic and genetic characteristics of zoonotic influenza viruses and development of candidate vaccine viruses for pandemic preparedness, September 2013
The development of representative candidate influenza vaccine viruses, coordinated by WHO, remains an essential component of the overall global strategy for pandemic preparedness. Comparisons of the candidate vaccine viruses with respect to antigenicity and their relationship to newly emerging viruses are ongoing and will be reported periodically by WHO.
(1) Influenza A(H5N1)
Since their re-emergence in 2003, highly pathogenic avian influenza A(H5N1) viruses have become enzootic in some countries and continue to cause outbreaks in poultry as well as sporadic human infections. The A(H5N1) viruses have diversified both genetically and antigenically leading to the need for multiple candidate vaccine viruses for pandemic preparedness purposes. This summary provides updates on the characterization of A(H5N1) viruses isolated from birds and humans, and the current status of the development of influenza A(H5N1) candidate vaccine viruses.
Influenza A(H5N1) activity: 19 February ? 23 September 2013
A(H5N1) viruses have been detected in birds in Africa and Asia. Human infections have been reported to the WHO by Cambodia, Egypt, Indonesia, and Viet Nam, countries in which infections have been detected in birds (Table 1).
Antigenic and genetic characteristics of A(H5N1) viruses
The nomenclature for phylogenetic relationships among the haemagglutinin (HA) genes of A(H5N1) viruses is defined in consultation with representatives of the WHO, the Food and Agriculture Organization of the United Nations (FAO), the World Organisation for Animal Health (OIE) and academic institutions. The updated nomenclature report can be found on WHO web site.(1)
Viruses circulating and characterized from 19 February to 23 September 2013 belonged to the following clades.
Clade 1.1 viruses were detected in poultry and humans in Cambodia and Viet Nam. Genetic characterization of the HA genes showed that these viruses were closely related to viruses detected previously in these countries (Figure 1). Some recent clade 1.1 viruses had reduced haemagglutination inhibition (HI) titres to post-infection ferret antisera raised against A/Viet Nam/1203/2004 and/or A/Cambodia/R0405050/2007 from which candidate vaccine viruses have been produced. Conversely, these viruses reacted well with post-infection ferret antisera raised against recent viruses isolated in Cambodia (Table 2). A new A/Cambodia/W0526301/2012-like candidate vaccine virus is proposed.
Clade 2.1.3.2 viruses continue to circulate in Indonesia. The HA gene sequence of a 2013 human virus was very similar to that of the candidate vaccine virus A/Indonesia/NIHRD11771/2011. No antigenic information is available.
Clade 2.2.1 viruses, similar to clade 2.2.1 viruses detected in previous years, were detected in poultry and humans in Egypt. These viruses reacted well with postinfection ferret antisera raised against available candidate vaccine viruses produced from A/Egypt/N03072/2010 and/or A/Egypt/2321-NAMRU3/2007.
Clade 2.3.2.1 viruses fall into 3 HA genetic groups as follows.
A/barn swallow/Hong Kong/D10-1161/2010-like viruses were detected in birds in China and Viet Nam but in reduced numbers compared to recent reporting periods. These viruses were genetically similar to viruses detected previously.
A/Hubei/1/2010-like viruses were detected in birds and/ or environmental samples from Bangladesh, China, India, Nepal, and Viet Nam (Figure 2). While some viruses reacted well with post-infection ferret antisera raised against the available candidate vaccine virus produced from A/Hubei/1/2010, others did not (Table 3). Due to these observations and the widespread distribution of these viruses, a new A/duck/Bangladesh/19097/2013-like candidate vaccine virus is proposed.
A/Hong Kong/6841/2010-like viruses were detected in China, Democratic People?s Republic of Korea, Indonesia (detected in birds illegally imported into Europe), and Viet Nam. Antigenically (Table 4) and genetically (Figure 3) some of these viruses have diverged from available candidate vaccine viruses, hence a new A/duck/Viet Nam/1584/2012-like candidate vaccine virus is proposed.
Clade 2.3.4.2 viruses were isolated from birds and environmental samples in China. The HA genes of these viruses were genetically similar to those of viruses detected previously. Antigenic characterization of these viruses is pending.
Clade 7.2 viruses were detected in China and Viet Nam. Genetically these viruses were similar to viruses characterized previously. These viruses had reduced reactivity to post-infection ferret antisera raised against available candidate vaccine viruses and further analyses are proposed to determine if production of additional candidates is needed.
Influenza A(H5N1) candidate vaccine viruses
Based on the available antigenic, genetic and epidemiologic data, A/duck/Bangladesh/19097/2013-like (clade 2.3.2.1), A/duck/Viet Nam/NCVD-1584/2012-like (clade 2.3.2.1) and A/Cambodia/W0526301/2012-like (clade 1.1) candidate vaccine viruses are proposed. The available and proposed candidate A(H5N1) vaccine viruses are listed in Table 5. On the basis of geographic spread, epidemiology and antigenic and genetic properties of A(H5N1) viruses in particular locations, national authorities may consider the use of one or more of these candidate vaccine viruses for pilot lot vaccine production, clinical trials and other pandemic preparedness purposes.
As the viruses continue to evolve, new A(H5N1) candidate vaccine viruses will be developed and announced as they become available. Institutions that wish to receive these candidate vaccine viruses should contact WHO at gisrs-whohq@who.int or the institutions listed in announcements published on the WHO website.(2)
(2) Influenza A(H9N2)
Influenza A(H9N2) viruses are enzootic in poultry populations in parts of Africa, Asia and the Middle East. The majority of viruses that have been sequenced belong to the G1, chicken/Beijing (Y280/G9), or Eurasian clades. Since 1998, when the first human infection was detected, the isolation of A(H9N2) viruses from humans and swine has been reported infrequently. In all human cases the associated disease symptoms have been mild and there has been no evidence of human-tohuman transmission.
Influenza A(H9N2) activity from 19 February to 23 September 2013
No human cases of A(H9N2) infection have been reported in this period. A(H9N2) viruses continue to be isolated from birds in many regions of the world.
Influenza A(H9N2) candidate vaccine viruses
Based on the current antigenic, genetic and epidemiologic data, no new A(H9N2) candidate vaccine viruses are proposed. The available A(H9N2) candidate vaccine viruses are listed in Table 6. Institutions that wish to receive candidate vaccine viruses should contact WHO at gisrs-whohq@who.int or the institutions listed in announcements published on the WHO website.(2)
(3) Influenza A(H7)
Influenza A(H7) viruses have been detected in poultry populations worldwide with the associated disease ranging from mild to severe. Occasionally, during outbreaks in poultry, human cases have been detected in those with direct poultry exposure. These infections often cause conjunctivitis or mild influenza-likeillness(3), (4) but some H7 infections, notably A(H7N9),(5) can cause severe respiratory disease.
Influenza A(H7N9) activity from February to 23 September 2013
The first instance of A(H7N9) infecting humans was reported to WHO on 31 March 2013. There were 135 human cases including 44 deaths. Geographic distribution of these human cases (and genetically related avian and/ or environmental samples) has been restricted to China. HA gene sequence and HI test comparison of A(H7N9) viruses isolated from humans and poultry suggest limited genetic and antigenic diversity among this group of viruses (Table 7 and Figure 4).
Influenza A(H7N9) candidate vaccine viruses
Based on the current epidemiologic data, A(H7N9) candidate vaccine viruses have been developed. Available A(H7N9) candidate vaccine viruses are shown in Table 8. Institutions that wish to receive candidate vaccine viruses should contact WHO at gisrs-whohq@who.int or the institutions listed in announcements published on the WHO website.(2)
Influenza A(H7N3) activity from 19 February to 23 September 2013
Highly pathogenic A(H7N3) viruses continue to circulate in poultry in Mexico. No human cases have been reported during this period.
Influenza A(H7N7) activity from 19 February to 23 September 2013
Since 14 August 2013 there have been 6 outbreaks of highly pathogenic avian influenza A(H7N7) in poultry in Italy. Three cases of A(H7N7) conjunctivitis were documented in personnel involved in culling operations with one case developing influenza-like illness. All individuals recovered without treatment. Genetically, the A(H7N7) viruses were similar to low pathogenic viruses circulating in wild birds in Europe and those causing sporadic and limited outbreaks in poultry in Central and Northern Europe (Figure 4). Antigenically, the A(H7N7) virus reacted well to post-infection ferret antisera raised against the candidate vaccine viruses A/turkey/Virginia/4529/2002 (H7N2) IBCDC-5 and A/mallard/Netherlands/12/2000 (H7N7) IBCDC-1.
Influenza A(H7) candidate vaccine viruses
Available A(H7) candidate vaccine viruses are shown in Table 9 additional to those available for A(H7N9) described in Table 8. Based on current data, no new A(H7N3) or A(H7N7) candidate vaccine viruses are proposed. Institutions that wish to receive candidate vaccine viruses should contact WHO at gisrs-whohq@who.int or the institutions listed in announcements published on the WHO website.(2)
(4) Influenza A(H3N2) variant (v)(6)
Influenza A(H3N2) viruses are enzootic in swine populations in most regions of the world. Depending on geographic location, the genetic and antigenic characteristics of these viruses differ. Human infections with swine A(H3N2) viruses have been documented in Asia, Europe and North America.(7)
Influenza A(H3N2)v activity from 19 February to 23 September 2013
Eighteen human cases of A(H3N2)v infection were reported in the United States (USA) during this reporting period.(8) These viruses were genetically and antigenically similar to previously characterized A(H3N2)v viruses. All cases had known exposure to swine at agricultural fairs. Similar viruses continue to be isolated from pigs in the USA.
Influenza A(H3N2)v candidate vaccine viruses
Based on the current antigenic, genetic and epidemiologic data, no new A(H3N2)v candidate vaccine viruses are proposed. Available candidate vaccine viruses are shown in Table 10. Institutions that wish to receive candidate vaccine viruses should contact WHO at gisrswhohq@who.int or Centers for Disease Control and Prevention, USA.
(5) Influenza A(H1N1)v
Influenza A(H1N1) viruses circulate in swine populations in many regions of the world. Depending on geographic location, the genetic characteristics of these viruses differ. Human infections with swine A(H1) viruses have been documented for many years.(9) Two human infections with A(H1N1)v viruses have been detected in the USA during the reporting period. These viruses are genetically similar to viruses circulating in swine in the region and to A(H1N1)v viruses detected in previous years.
Influenza A(H1N1)v candidate vaccine viruses
Based on a risk assessment of the antigenic and genetic characteristics of the A(H1N1)v viruses, candidate vaccine viruses are not proposed at this time.
(6) Influenza A(H6N1)
A human infection with A(H6N1) virus was detected in Taiwan, China in May.(10) No human A(H6N1) infections had been detected previously. The virus was genetically similar to viruses isolated from chickens in Taiwan, China but different from A(H6N1) viruses circulating in poultry in other regions of Asia.
Influenza A(H6N1) candidate vaccine viruses
Based on a risk assessment, no candidate vaccine viruses have been proposed at this time.
(...)
________
(1) Updated unified nomenclature system for the highly pathogenic H5N1 avian influenza viruses. Geneva, World Health Organization, 2011 (http://www.who.int/influenza/gisrs_laboratory/h5n1_nomenclature/en/, accessed September 2013).
(2) Candidate vaccine viruses and potency testing reagents for influenza A(H5N1). Available at http://www.who.int/influenza/vaccines/virus/en/, accessed September 2013.
(3) Tweed, SA et al. Human illness from avian influenza H7N3, British Columbia. Emerging Infectious Diseases, 2004, 10(12): 2196?2199.
(4) de Jong MC et al. Intra- and interspecies transmission of H7N7 highly pathogenic avian influenza virus during the avian influenza epidemic in the Netherlands in 2003. Revue scientifique et technique de l?Office international des ?pizooties (OIE), 2009, 28(1):333?340.
(5) Avian influenza A(H7N9) virus. Available at http://www.who.int/influenza/human_animal_interface/influenza_h7n9/en/, accessed September 2013.
(6) Standardization of terminology for the variant A(H3N2) virus recently infecting humans. Available at http://www.who.int/influenza/gisrs_laboratory/terminology_ah3n2v/en/index.html/, accessed September 2013.
(7) Myers KP et al. Cases of swine influenza in humans: a review of the literature. Clinical Infectious Diseases, 2007, 44:1084?1088.
(8) Situation summary on influenza A (H3N2) variant viruses (H3N2v). Available at http://www.cdc.gov/flu/swineflu/h3n2v-situation.htm, accessed September 2013.
(9) Shu B et al. Genetic analysis and antigenic characterization of swine origin influenza viruses isolated from humans in the United States, 1990?2010. Virology, 2012, 422:151.
(10) Yuan, J. et al. Origin and molecular characteristics of a novel 2013 avian influenza A(H6N1) virus causing human infection in Taiwan, 2013. Clinical Infectious Diseases, 2013 [Epub ahead of print].
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