Genetic and Antigenic Evolution of Influenza A (H3N2) Virus Neuraminidase

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of Influenza A (H3N2) Virus

Neuraminidase

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of the Erasmus Postgraduate School Molecular Medicine. The research presented in ƥĺĿƙ ƥĺĚƙĿƙ ǅîƙ ǶŠîŠČĿîŕŕǋ ƙƭƎƎūƑƥĚē ċǋ îŠ sØ~ɠ×T T ĳƑîŠƥ îŠē sTO ČūŠƥƑîČƥƙ Šūɍ OO¬sȃȇȇȃȁȁȈȁȁȁȂȁ îŠēOO¬sȃȈȃȃȁȂȅȁȁȁȁȉ ɍ GĿŠîŠČĿîŕƙƭƎƎūƑƥĲūƑƥĺĚƎƑĿŠƥĿŠĳūĲƥĺĿƙƥĺĚƙĿƙǅîƙƎƑūǄĿēĚēċǋɇ×ĿƑūČŕĿŠĿČƙĿūƙČĿĚŠČĚƙ ×ɈH¤ĿŠƙƥƑƭŞĚŠƥƙɈè/T¬¬ɈHƑĚĿŠĚƑĿūɠ~ŠĚɈ£TH/s T¬sɇ ȊȈȉɠȊȅɠȇȄȈȆɠȃȉȈɠȊ gîǋɠūƭƥɇ 'îǄĿēēĚHƑūūƥɚƎĚƑƙūūŠŕĿŏŒƎƑūĚĲƙČĺƑĿĲƥɍŠŕɛ ūǄĚƑēĚƙĿĳŠɇ ūƑŠěǄîŠgĚƭǄĚƑĚŠʨeĿŞØĚƙƥĳĚĚƙƥ ĺîƎƥĚƑēĚƙĿĳŠɇ ūƑŠěǄîŠgĚƭǄĚƑĚŠʨeĿŞØĚƙƥĳĚĚƙƥ ¡ƑĿŠƥɇ ¤ĿēēĚƑƎƑĿŠƥɚǅǅǅɍƑĿēēĚƑƎƑĿŠƥɍŠŕɛ ʫeɍɍØĚƙƥĳĚĚƙƥɈȃȁȂȊ ŕŕƑĿĳĺƥƙƑĚƙĚƑǄĚēɍsūƎîƑƥūĲƥĺĿƙƥĺĚƙĿƙŞîǋċĚƑĚƎƑūēƭČĚēūƑƥƑîŠƙŞĿƥƥĚēɈĿŠîŠǋĲūƑŞ ūƑċǋîŠǋŞĚîŠƙɈǅĿƥĺūƭƥƥĺĚƎĚƑŞĿƙƙĿūŠūĲƥĺĚîƭƥĺūƑɍ

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Genetische en antigene evolutie van het ŠĚƭƑîŞĿŠĿēîƙĚǄîŠɚOȄsȃɛĿŠǷƭĚŠǕîǄĿƑƭƙƙĚŠ

Proefschrift

ƥĚƑǄĚƑŒƑĿŏĳĿŠĳǄîŠēĚĳƑîîēǄîŠēūČƥūƑîîŠēĚ Erasmus Universiteit Rotterdam

ūƎĳĚǕîĳǄîŠēĚ ƑĚČƥūƑŞîĳŠĿǶČƭƙ Prof.dr. R.C.M.E. Engels

en volgens besluit van het College voor Promoties.

'ĚūƎĚŠċîƑĚǄĚƑēĚēĿĳĿŠĳǕîŕƎŕîîƥƙǄĿŠēĚŠūƎ ēūŠēĚƑēîĳȈŞîîƑƥȃȁȂȊūŞȂȆɇȄȁƭƭƑ

door

Kim Birgitta Westgeest ĳĚċūƑĚŠƥĚ'ĚŠOîîĳ

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~ǄĚƑĿĳĚŕĚēĚŠɇ ¡ƑūĲɍēƑɍqɍ¡ɍHɍeūūƎŞîŠƙ

¡ƑūĲɍēƑɍHɍGɍ¤ĿŞŞĚŕǕǅîîŠ

¡ƑūĲɍēƑɍ¤ɍØɍOĚŠēƑĿŒƙ

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ĺîƎƥĚƑȂ TŠƥƑūēƭČƥĿūŠ Ȋ ĺîƎƥĚƑȃ HĚŠĚƥĿČĚǄūŕƭƥĿūŠūĲƥĺĚŠĚƭƑîŞĿŠĿēîƙĚūĲĿŠǷƭĚŠǕî

ɚOȄsȃɛǄĿƑƭƙĚƙĲƑūŞȂȊȇȉƥūȃȁȁȊîŠēĿƥƙČūƑƑĚƙƎūŠɠ dence to haemagglutinin evolution.

Journal of General Virology 2012

ȃȆ ĺîƎƥĚƑȄ HĚŠūŞĚǅĿēĚîŠîŕǋƙĿƙūĲƑĚîƙƙūƑƥŞĚŠƥîŠēĚǄūŕƭƥĿūŠūĲ ĺƭŞîŠĿŠǷƭĚŠǕîɚOȄsȃɛǄĿƑƭƙĚƙČĿƑČƭŕîƥĿŠĳċĚƥǅĚĚŠ ȂȊȇȉîŠēȃȁȂȂɍ Journal of Virology 2014 ȅȈ ĺîƎƥĚƑȅ 'ĿƙČūƑēîŠƥîŠƥĿĳĚŠĿČēƑĿĲƥūĲŠĚƭƑîŞĿŠĿēîƙĚîŠēĺîĚŞɠ îĳĳŕƭƥĿŠĿŠĿŠOȂsȂîŠēOȄsȃĿŠǷƭĚŠǕîǄĿƑƭƙĚƙɍ

Proceedings of the National Academy of Sciences 2011

ȈȈ

ĺîƎƥĚƑȆ ŠūƎƥĿŞĿǕĚēĚŠǕǋŞĚɠŕĿŠŒĚēŕĚČƥĿŠîƙƙîǋƥūŞĚîƙƭƑĚ ĿŠǷƭĚŠǕîǄĿƑƭƙŠĚƭƑîŞĿŠĿēîƙĚĿŠĺĿċĿƥĿūŠîŠƥĿċūēǋ titres in human sera.

Journal of Virological Methods 2014

ȊȄ

ĺîƎƥĚƑȇ ~ƎƥĿŞĿǕîƥĿūŠūĲîŠĚŠǕǋŞĚɠŕĿŠŒĚēŕĚČƥĿŠîƙƙîǋƙƭĿƥîċŕĚ ĲūƑƑîƎĿēîŠƥĿĳĚŠĿČČĺîƑîČƥĚƑĿǕîƥĿūŠūĲƥĺĚŠĚƭƑîŞĿŠĿɠ ēîƙĚūĲĺƭŞîŠĿŠǷƭĚŠǕîɚOȄsȃɛǄĿƑƭƙĚƙɍ

Journal of Virological Methods 2015

ȂȂȄ ĺîƎƥĚƑȈ qîƎƎĿŠĳƥĺĚŠƥĿĳĚŠĿČ/ǄūŕƭƥĿūŠūĲƥĺĚsȃsĚƭƑîŞĿŠɠ ĿēîƙĚūĲOƭŞîŠTŠǷƭĚŠǕî×ĿƑƭƙĚƙĲƑūŞȂȊȆȈƥū ȃȁȂȃɍ In preparation ȂȄȄ ĺîƎƥĚƑȉ ¬ƭŞŞîƑĿǕĿŠĳēĿƙČƭƙƙĿūŠ ȂȇȆ ĺîƎƥĚƑȊ References ȂȉȂ ĺîƎƥĚƑȂȁ Nederlandse samenvatting ȃȃȄ ĺîƎƥĚƑȂȂ 'îŠŒǅūūƑēʋċūƭƥƥĺĚîƭƥĺūƑ Curriculum vitae PhD portfolio List of publications ȃȄȄ 242 243 246

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Ts¹¤~'À ¹T~s

TŠǷƭĚŠǕîǄĿƑƭƙĺĿƙƥūƑǋ ¹ĺĚ ǶƑƙƥ ēūČƭŞĚŠƥĚē ĿŠǷƭĚŠǕî ǄĿƑƭƙ ǅîƙ ĿƙūŕîƥĚē ĲƑūŞ ƙǅĿŠĚ ĿŠ ȂȊȄȂȂ_{, and the} ǶƑƙƥ ĺƭŞîŠ ĿƙūŕîƥĚ ǅîƙ ƑĚƎūƑƥĚē ĿŠ ȂȊȄȄȃ_{ɍ OūǅĚǄĚƑɈ ĿŠ ƑĚƥƑūƙƎĚČƥɈ ƥĺĚ ǶƑƙƥ ǄĚƑĿǶĚē} ēĚƙČƑĿƎƥĿūŠ ūĲ ĿŠǷƭĚŠǕî ēîƥĚƙ ċîČŒ ƥū ȂȉȈȉɈ ǅĺĚƑĚ Ŀƥ ǅîƙ ēĚƙČƑĿċĚē îƙ î ČūŠƥîĳĿūƭƙ ēĿƙĚîƙĚ ūĲ ƎūƭŕƥƑǋ îƙƙūČĿîƥĚē ǅĿƥĺ ĺĿĳĺ ŞūƑƥîŕĿƥǋɍ ¹ĺĚ ēĿƙĚîƙĚ ǅîƙ ĿŠĿƥĿîŕŕǋ ČūŠĲƭƙĚē ǅĿƥĺĲūǅŕČĺūŕĚƑîɈîŠēĿƥǅîƙŠūƥƭŠƥĿŕȂȊȆȆƥĺîƥƥĺĚČîƭƙîƥĿǄĚîĳĚŠƥūĲƥĺĿƙēĿƙĚîƙĚǅîƙ ƙĺūǅŠƥūċĚîŠîǄĿîŠĿŠǷƭĚŠǕîǄĿƑƭƙȄ_. TŠǷƭĚŠǕîǄĿƑƭƙƥîǊūŠūŞǋ TŠǷƭĚŠǕî ǄĿƑƭƙĚƙ îƑĚ ŞĚŞċĚƑƙ ūĲ ƥĺĚ Orthomyxoviridae ĲîŞĿŕǋ ČūŞƎƑĿƙĿŠĳ ĚŠǄĚŕūƎĚēɈ ŠĚĳîƥĿǄĚɠƙĚŠƙĚɈ ƙĿŠĳŕĚɠƙƥƑîŠēĚēɈ ƙĚĳŞĚŠƥĚē ¤s ǄĿƑƭƙĚƙȅ_{. The}

ĲîŞĿŕǋ ūĲ Orthomyxoviridae is divided over seven generaȆ_{ɇ ŕƎĺîĿŠǷƭĚŠǕîǄĿƑƭƙɈ}

ĚƥîĿŠǷƭĚŠǕîǄĿƑƭƙɈ'ĚŕƥîĿŠǷƭĚŠǕîǄĿƑƭƙɈHîŞŞîĿŠǷƭĚŠǕîǄĿƑƭƙɈTƙîǄĿƑƭƙɈ£ƭîƑîŠŏîǄĿƑƭƙɈ îŠē¹ĺūĳūƥūǄĿƑƭƙɍŕŕĿŠĲĚČƥĺƭŞîŠƙɈĚǊČĚƎƥ'ĚŕƥîĿŠǷƭĚŠǕîǄĿƑƭƙîŠēTƙîǄĿƑƭƙɍTŠĲĚČƥĿūƭƙ ƙîŕŞūŠîŠîĚŞĿîǄĿƑƭƙɈūĲƥĺĚTƙîǄĿƑƭƙĳĚŠƭƙɈĿƙĲūƭŠēĚǊČŕƭƙĿǄĚŕǋĿŠǶƙĺȇ_{ɈîŠēĿŠǷƭĚŠǕî'}

ǄĿƑƭƙɚT'×ɛɈūĲƥĺĚ'ĚŕƥîĿŠǷƭĚŠǕîǄĿƑƭƙĳĚŠƭƙɈǅîƙĿƙūŕîƥĚēĲƑūŞƙǅĿŠĚîŠēƥĺĚĿƑƎƑĿŞîƑǋ natural reservoir, cattleȈ_{ɍ ¹ĺĚ ĳĚŠƭƙ ¹ĺūĳūƥūǄĿƑƭƙ îƑĚ î ĳƑūƭƎ ūĲ îƑƥĺƑūƎūēɠċūƑŠĚ}

ǄĿƑƭƙĚƙ ǅĺĿČĺ Şîǋ ƎĚƑĿūēĿČîŕŕǋ ĿŠĲĚČƥ ĺƭŞîŠƙȉɈȊ_{ɍ £ƭîƑîŠŏîǄĿƑƭƙ ŞĚŞċĚƑƙ îƎƎĚîƑ ƥū} ƎƑĚēūŞĿŠîŠƥŕǋūČČƭƑĿŠƙūĲƥƥĿČŒƙîŠēîƐƭîƥĿČċĿƑēƙȂȁ_{ɍTŠǷƭĚŠǕîǄĿƑƭƙɚT×ɛîŠēĿŠǷƭĚŠǕî} ǄĿƑƭƙɚT×ɛɈƥĺĚūŠŕǋƙƎĚČĿĚƙūĲƥĺĚŕƎĺîĿŠǷƭĚŠǕîǄĿƑƭƙîŠēĚƥîĿŠǷƭĚŠǕîǄĿƑƭƙĳĚŠĚƑîɈ ƑĚƙƎĚČƥĿǄĚŕǋɈ îƑĚ ƑĚƙƎūŠƙĿċŕĚ ĲūƑ ĚƎĿēĚŞĿČ ĿŠǷƭĚŠǕî ūƭƥċƑĚîŒƙ ĿŠ ĺƭŞîŠƙɍ TŠǷƭĚŠǕî ǄĿƑƭƙ ɚT ×ɛɈ ƥĺĚ ūŠŕǋ ƙƎĚČĿĚƙ ūĲ ƥĺĚ HîŞŞîĿŠǷƭĚŠǕîǄĿƑƭƙ ĳĚŠƭƙɈ Ŀƙ îƙƙūČĿîƥĚē ǅĿƥĺ ƙƎūƑîēĿČîŠēŞĿŕēČūŞŞūŠČūŕēɠŕĿŒĚĿŕŕŠĚƙƙɈîŕƙūĿŠĺƭŞîŠƙȅ_{ɍTŠîēēĿƥĿūŠƥūĺƭŞîŠƙɈT×} ČîŠĿŠĲĚČƥîċƑūîēƑîŠĳĚūĲŞîŞŞîŕĿîŠîŠēîǄĿîŠƙƎĚČĿĚƙɈƭŠŕĿŒĚT×îŠēT ×Ɉîŕƥĺūƭĳĺ îŠ T× ĺîƙ ċĚĚŠ ĿēĚŠƥĿǶĚē ĿŠ ƑîǋɠǶŠŠĚē ǶƙĺȂȂ_{ɍ qūƑĚūǄĚƑɈ T× Ŀƙ ƑĚƙƎūŠƙĿċŕĚ ĲūƑ ƥĺĚ} ŞîŏūƑĿŠǷƭĚŠǕîƎîŠēĚŞĿČƙĿŠĺƭŞîŠƙƥĺƑūƭĳĺūƭƥĺĿƙƥūƑǋȇ_. 'ĿǄĿƙĿūŠĿŠƥūƙƭċƥǋƎĚƙūĲƥĺĚT×ƙƎĚČĿĚƙĿƙċîƙĚēūŠƥĺĚîŠƥĿĳĚŠĿČƎƑūƎĚƑƥĿĚƙūĲ ƥĺĚŞîŏūƑĳŕǋČūƎƑūƥĚĿŠƙɈɪĺîĚŞîĳĳŕƭƥĿŠĿŠɫɚOūƑOɛîŠēɪŠĚƭƑîŞĿŠĿēîƙĚɫɚsūƑsɛȅ_{; the} ƙƭċƥǋƎĚƙîƑĚŕîċĚŕŕĚēǅĿƥĺîŠOŠƭŞċĚƑîŠēîŠsŠƭŞċĚƑȂȃ_{ɍ¹ūēîƥĚɈĚĿĳĺƥĚĚŠO}ȂȄɝȂȆ îŠēĚŕĚǄĚŠsȂȄɈȂȇɈȂȈ_{ƙƭċƥǋƎĚƙĺîǄĚċĚĚŠĲūƭŠēĿŠŠîƥƭƑĚɈūĲǅĺĿČĺƥĺĚċîƥT×ƙƭƑĲîČĚ} ĳŕǋČūƎƑūƥĚĿŠƙɜOȂȈɈOȂȉɈsȂȁɈîŠēsȂȂɜîƑĚƑĚĲĚƑƑĚēƥūîƙOɠŕĿŒĚîŠēsɠŕĿŒĚȂȉ_ɍTŠ îēēĿƥĿūŠƥūƥĺĚƙƭċƥǋƎĚĿŠĲūƑŞîƥĿūŠɈT×ŠūŞĚŠČŕîƥƭƑĚĿŠČŕƭēĚƙƥĺĚĺūƙƥūĲūƑĿĳĿŠɚǅĿƥĺ ƥĺĚĚǊČĚƎƥĿūŠūĲĺƭŞîŠɠūƑĿĳĿŠǄĿƑƭƙĚƙǅĺĚƑĚŠūĺūƙƥūĲūƑĿĳĿŠēĚƙĿĳŠîƥĿūŠĿƙĳĿǄĚŠɛɈ ĳĚūĳƑîƎĺĿČŕūČîƥĿūŠūĲĿŠĿƥĿîŕĿƙūŕîƥĿūŠɈƙƥƑîĿŠŠƭŞċĚƑɈîŠēǋĚîƑūĲĿƙūŕîƥĿūŠȂȊ_{ɍGūƑĚǊîŞƎŕĚɈ}

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ɓēƭČŒɓŕċĚƑƥîɓȄȆɓȈȇɚOȂsȂɛĿƙîŠT×ūĲēƭČŒūƑĿĳĿŠūĲƥĺĚOȂsȂƙƭċƥǋƎĚɈƥĺĚȄȆƥĺ ƙƥƑîĿŠĿƙūŕîƥĚēĿŠŕċĚƑƥîĿŠȂȊȈȇɍ¹ĺĚŞîĿŠƑĚƙĚƑǄūĿƑūĲT×ĿƙǅĿŕēîƐƭîƥĿČċĿƑēƙɈîŠēƥĺĚ OȂɠOȂȇîŠēsȂɠsȊƙƭċƥǋƎĚƙîƑĚĲūƭŠēǅĿƥĺĿŠƥĺĚƙĚƙƎĚČĿĚƙɍŕƥĺūƭĳĺƙĚǄĚƑîŕēĿĲĲĚƑĚŠƥ ƙƭċƥǋƎĚƙĺîǄĚČîƭƙĚēǕūūŠūƥĿČĿŠĲĚČƥĿūŠƙɈƙƭČĺîƙOȆsȂȃȁɈȃȂ_ɈOȆsȃȃȃ_ɈOȈsȃȃȄɈȃȅ_ɈOȈsȄȃȆ_,

OȈsȈȃȇɈȃȈ_ɈOȊsȃȃȉɝȄȁ_{ɈîŠēOȂȁsȈ}ȅ_{ɈūŠŕǋƙƭċƥǋƎĚƙOȂsȂɈOȃsȃɈîŠēOȄsȃĺîǄĚČîƭƙĚē}

ƎîŠēĚŞĿČƙîŠēĚƎĿēĚŞĿČƙĿŠƥĺĚŕîƙƥČĚŠƥƭƑǋȅɈȄȂ_. TŠǷƭĚŠǕîǄĿƑƭƙĿŠĺƭŞîŠƙ ƎƎƑūǊĿŞîƥĚŕǋɈ ȆɝȂȆ ʣ ūĲ ƥĺĚ ǅūƑŕē ƎūƎƭŕîƥĿūŠ Ŀƙ ĿŠĲĚČƥĚē ċǋ ĿŠǷƭĚŠǕî ĚîČĺ ǋĚîƑɈ ƑĚƙƭŕƥĿŠĳĿŠîŠĚƙƥĿŞîƥĚēƥĺƑĚĚƥūǶǄĚŞĿŕŕĿūŠĺūƙƎĿƥîŕĿǕîƥĿūŠƙîŠēȃȊȁɈȁȁȁƥūȇȆȁɈȁȁȁ ēĚîƥĺƙîŠŠƭîŕŕǋȄȃ_{ɍ¹ĺĿƙǋĚîƑŕǋƎĺĚŠūŞĚŠūŠĿƙƑĚĲĚƑƑĚēƥūîƙɪƙĚîƙūŠîŕǷƭɫūƑɪĚƎĿēĚŞĿČ} ĿŠǷƭĚŠǕîɫɍ ¹ĺĚ ČŕĿŠĿČîŕ ƎƑĚƙĚŠƥîƥĿūŠ ūĲ ĚƎĿēĚŞĿČ ĿŠǷƭĚŠǕî Ŀƙ Šūƥ ƙƥƑîĿĳĺƥĲūƑǅîƑē îŠē ēĚƎĚŠēƙūŠƥĺĚŠîƥƭƑĚūĲƥĺĚǄĿƑƭƙîŠēƥĺĚČūŠēĿƥĿūŠūĲƥĺĚƎîƥĿĚŠƥɍTƥŞîǋǄîƑǋĲƑūŞ îƙǋŞƎƥūŞîƥĿČ ƥū î ƎƑĿŞîƑǋ ǄĿƑîŕ ƎŠĚƭŞūŠĿî ūƑ îČƭƥĚ ƑĚƙƎĿƑîƥūƑǋ ēĿƙƥƑĚƙƙ ƙǋŠēƑūŞĚɍ TŠ ĳĚŠĚƑîŕɈ ƥĺĚ ŞîŠĿĲĚƙƥîƥĿūŠƙ ūĲ ƭŠČūŞƎŕĿČîƥĚē ĿŠǷƭĚŠǕî ēƭƑĿŠĳ îŠ ĚƎĿēĚŞĿČ îƑĚ ƑĚŕîƥĿǄĚŕǋŞĿŕēɍ ūŞŞūŠƙǋŞƎƥūŞƙĿŠČŕƭēĚƙūƑĚƥĺƑūîƥɈƑĺĿŠūƑƑĺūĚîɈŞǋîŕĳĿîɈĺĚîēîČĺĚɈ ĲĚǄĚƑĿƙĺŠĚƙƙɈŕūƙƙūĲîƎƎĚƥĿƥĚɈŞîŕîĿƙĚɈîŠēɓūƑǅĚîŒŠĚƙƙɍsūŠĚƥĺĚŕĚƙƙɈƥĺĚîƎƎĚîƑîŠČĚ ūĲ ĲĚǄĚƑ îŠē ēƑǋ Čūƭĳĺ ǅĿƥĺĿŠ ȅȉ ĺ ūĲ ƙǋŞƎƥūŞ ūŠƙĚƥ ƙĿĳŠĿǶČîŠƥŕǋ ēĿƙƥĿŠĳƭĿƙĺ T× ĿŠĲĚČƥĿūŠ ĲƑūŞ ūƥĺĚƑ ǄĿƑîŕ ūƑ ċîČƥĚƑĿîŕ ƎîƥĺūĳĚŠƙ ČîƭƙĿŠĳ ĿŠǷƭĚŠǕîɠŕĿŒĚ ĿŕŕŠĚƙƙɍ TŠ ƑĿƙŒ ĳƑūƭƎƙūŠƥĺĚūƥĺĚƑĺîŠēɈĿŠǷƭĚŠǕîŞîǋŕĚîēƥūĺūƙƎĿƥîŕĿǕîƥĿūŠūƑĚǄĚŠēĚîƥĺɚƑūƭĳĺŕǋ ŠĿŠĚƥĚĚŠĺƭŠēƑĚēîŠēĚĿĳĺƥĺƭŠēƑĚēîŠŠƭîŕČîƙĚƙɈƑĚƙƎĚČƥĿǄĚŕǋɈĿŠƥĺĚsĚƥĺĚƑŕîŠēƙȄȄɈȄȅ_ɛɍ ¡ĚūƎŕĚ ĿŠ ƥĺĚƙĚ ƑĿƙŒ ĳƑūƭƎƙ ĿŠČŕƭēĚ ČĺĿŕēƑĚŠ ċĚŕūǅ ƥĺĚ îĳĚ ūĲ ȃɈ îēƭŕƥƙ ūŕēĚƑ ƥĺîŠ ȇȆ ǋĚîƑƙūĲîĳĚɈîŠēîēƭŕƥƙǅĿƥĺŞĚēĿČîŕČūŠēĿƥĿūŠƙƙƭČĺîƙēĿîċĚƥĚƙɈƑĚƙƎĿƑîƥūƑǋēĿƙĚîƙĚɈ or cardiovascular disease. ¹ĺĚǅūƑŕēǅĿēĚƙƎƑĚîēūĲîŠĚǅĿŠǷƭĚŠǕîǄĿƑƭƙƙƭċƥǋƎĚɈūƑɪƎîŠēĚŞĿČĿŠǷƭĚŠǕîɫɈ ĿƙēĚČŕîƑĚēūŠČĚƥĺĚƑĚĿƙĿŠČƑĚîƙĚēîŠēƙƭƙƥîĿŠĚēĺƭŞîŠɠƥūɠĺƭŞîŠƥƑîŠƙŞĿƙƙĿūŠǅĿƥĺĿŠ the general populationȄȆ_{ɍŕîƑĳĚƎūƑƥĿūŠūĲƥĺĚƎūƎƭŕîƥĿūŠǅĿŕŕċĚĿŞŞƭŠūŕūĳĿČîŕŕǋŠîĿǄĚ}

ƥūǅîƑēƙƥĺĚŠĚǅƙƭċƥǋƎĚɈǅĺĿČĺČîŠŕĚîēƥūƙĚƑĿūƭƙĺĚîŕƥĺƎƑūċŕĚŞƙîŠēĚǄĚŠĲîƥîŕ ūƭƥČūŞĚƙĿŠƥĺĚĳĚŠĚƑîŕƎūƎƭŕîƥĿūŠĿŠČŕƭēĿŠĳîŞūŠĳĺĚîŕƥĺǋɈǋūƭŠĳîēƭŕƥƙȄȇ_{. There were}

ĲūƭƑŞîŏūƑĿŠǷƭĚŠǕîƎîŠēĚŞĿČƙĿŠƥĺĚƎîƙƥČĚŠƥƭƑǋȄȈ_{ɚGĿĳƭƑĚȂɛɇƥĺĚȂȊȂȉƎîŠēĚŞĿČČîƭƙĚē}

ċǋĿŠǷƭĚŠǕîOȂsȂɚɚOȂsȂɛɛǄĿƑƭƙɈƥĺĚȂȊȆȈɠȂȊȆȉƎîŠēĚŞĿČČîƭƙĚēċǋĿŠǷƭĚŠǕî OȃsȃɚɚOȃsȃɛɛǄĿƑƭƙɈƥĺĚȂȊȇȉƎîŠēĚŞĿČČîƭƙĚēċǋĿŠǷƭĚŠǕîOȄsȃɚɚOȄsȃɛɛ ǄĿƑƭƙɈ îŠē ƥĺĚ ȃȁȁȊ OȂsȂ ƎîŠēĚŞĿČ ČîƭƙĚē ċǋ ĿŠǷƭĚŠǕî OȂsȂƎēŞȁȊ ɚɚOȂsȂɛ ƎēŞȁȊɛǄĿƑƭƙɍĲƥĚƑƥĺĚȂȊȂȉƎîŠēĚŞĿČɈƥĺĚɚOȂsȂɛǄĿƑƭƙČîƭƙĚēîŠŠƭîŕĚƎĿēĚŞĿČƙ ƭŠƥĿŕƥĺĚȂȊȆȈɠȂȊȆȉƎîŠēĚŞĿČǅĺĚƑĚĿƥǅîƙƑĚƎŕîČĚēċǋƥĺĚɚOȃsȃɛǄĿƑƭƙǅĺĿČĺƥĺĚŠ

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ċĚČîŞĚƥĺĚƙĚîƙūŠîŕĿŠǷƭĚŠǕîƭŠƥĿŕƥĺĚȂȊȇȉƎîŠēĚŞĿČɍɚOȃsȃɛîŠēɚOȄsȃɛǄĿƑƭƙĚƙ ČūČĿƑČƭŕîƥĚēĲƑūŞȂȊȇȉƭŠƥĿŕȂȊȈȂɈîĲƥĚƑǅĺĿČĺɚOȃsȃɛǄĿƑƭƙĚƙċĚČîŞĚĚǊƥĿŠČƥĿŠƥĺĚ human populationȄȉɈȄȊ_{ɍɚOȄsȃɛǄĿƑƭƙĚƙĺîǄĚċĚĚŠîƙĚƑĿūƭƙČîƭƙĚūĲĿŠǷƭĚŠǕîĚƎĿēĚŞĿČƙ}

ƙĿŠČĚƥĺĚĿƑĿŠƥƑūēƭČƥĿūŠĿŠȂȊȇȉɈǅĿƥĺƙĿĳŠĿǶČîŠƥŞūƑċĿēĿƥǋîŠēŞūƑƥîŕĿƥǋȄȃɈȅȁ_{ɍ¹ĺĚȂȊȈȈ} ɚOȂsȂɛǄĿƑƭƙūƭƥċƑĚîŒɈǅĺĿČĺČŕūƙĚŕǋƑĚƙĚŞċŕĚēǄĿƑƭƙĚƙƥĺîƥĺîēČĿƑČƭŕîƥĚēĿŠƥĺĚĚîƑŕǋ ȂȊȆȁƙȅȂ_{ɈēĿēŠūƥČîƭƙĚîƎîŠēĚŞĿČĲūƑŞîŕŕǋɈċĚČîƭƙĚĿƥǅîƙŠūƥîŠūǄĚŕǄĿƑƭƙƙƭċƥǋƎĚɈ} ŠūƑēĿēĿƥƑĚƎŕîČĚɚOȄsȃɛǄĿƑƭƙĚƙɍTŠƙƥĚîēɈĿƥČūČĿƑČƭŕîƥĚēǅĿƥĺɚOȄsȃɛǄĿƑƭƙĚƙƭŠƥĿŕƥĺĚ ȃȁȁȊOȂsȂƎîŠēĚŞĿČɈǅĺĚŠĿƥǅîƙƑĚƎŕîČĚēċǋƥĺĚɚOȂsȂɛƎēŞȁȊǄĿƑƭƙǅĺĿČĺɈƥūĳĚƥĺĚƑ ǅĿƥĺɚOȄsȃɛǄĿƑƭƙĚƙɈČūŠƥĿŠƭĚƙƥūČîƭƙĚĚƎĿēĚŞĿČƙȄȃ_. TŠǷƭĚŠǕîǄĿƑƭƙĳĚŠūŞĚîŠēĿƥƙĚŠČūēĚēƎƑūƥĚĿŠƙ ¹ĺĚT×ĳĚŠūŞĚĿƙēĿǄĿēĚēĿŠƥūĚĿĳĺƥĳĚŠĚƙĚĳŞĚŠƥƙǄîƑǋĿŠĳĿŠŕĚŠĳƥĺîŠēČūŠƙĿƙƥĿŠĳ ūĲɇ ċîƙĿČ ƎūŕǋŞĚƑîƙĚ ȃ ɚ¡ȃɛɈ ċîƙĿČ ƎūŕǋŞĚƑîƙĚ Ȃ ɚ¡ȂɛɈ îČĿēĿČ ƎūŕǋŞĚƑîƙĚ ɚ¡ɛɈ OɈ ŠƭČŕĚūČîƎƙĿē ƎƑūƥĚĿŠ ɚs¡ɛɈ sɈ ŞîƥƑĿǊ ɚqɛɈ îŠē ŠūŠƙƥƑƭČƥƭƑîŕ ƎƑūƥĚĿŠ ɚs¬ɛɍ ¹ĺĚ ĳĚŠĚ ƙĚĳŞĚŠƥƥĺîƥĚŠČūēĚƙ¡ȂîŕƙūĚŠČūēĚƙîŠsɠƥƑƭŠČîƥĚēĲūƑŞūĲ¡ȂƙƥîƑƥĿŠĳîƥČūēūŠ ȅȁ ɚ¡Ȃɠsȅȁɛȅȃ_{Ɉ îŠē ¡ȂɠĲƑîŞĚ ȃ ɚ¡ȂɠGȃɛ ĚǊƎƑĚƙƙĚē ƥĺƑūƭĳĺ îŠ îŕƥĚƑŠîƥĿǄĚ ūƎĚŠ} ƑĚîēĿŠĳĲƑîŞĚɚ~¤GɛȅȄ_{ɍ¹ĺĚĳĚŠĚƙĚĳŞĚŠƥƥĺîƥĚŠČūēĚƙ¡îŕƙūĚŠČūēĚƙ¡ɠÝƥĺƑūƭĳĺ} A(H1N1) A(H2N2) A(H3N2) A(H1N1)pdm09 A(H1N1) 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year GĿĳƭƑĚȂʯ¤ĚČūƑēĚēƎîŠēĚŞĿČîŠēĚƎĿēĚŞĿČĿŠǷƭĚŠǕîǄĿƑƭƙĚƙūĲƥĺĚƎîƙƥČĚŠƥƭƑǋɍ Horizontal îƑƑūǅƙƙĺūǅƥĺĚƎĚƑĿūēūĲČĿƑČƭŕîƥĿūŠūĲƥĺĚƙƎĚČĿǶČĿŠǷƭĚŠǕîǄĿƑƭƙƙƭċƥǋƎĚîĲƥĚƑƥĺĚƎîŠēĚŞĿČ ūŠƙĚƥ ɚƙūŕĿē ČĿƑČŕĚƙɛɍ ¹ĺĚ ċŕƭĚ îƑƑūǅƙ ƙĺūǅ ƥĺĚ ȂȊȂȉ ƎîŠēĚŞĿČ ČîƭƙĚē ċǋ ĿŠǷƭĚŠǕî OȂsȂ (A(H1N1)) virus and 1977 A(H1N1) virus outbreak. The latter was not a pandemic as these viruses closely resembled viruses that had circulated in the early 1950s. The green arrow shows the 1957-ȂȊȆȉƎîŠēĚŞĿČČîƭƙĚēċǋĿŠǷƭĚŠǕîOȃsȃɚɚOȃsȃɛɛǄĿƑƭƙîŠēƥĺĚƑĚēîƑƑūǅĿŕŕƭƙƥƑîƥĚƙƥĺĚ ȂȊȇȉƎîŠēĚŞĿČČîƭƙĚēċǋĿŠǷƭĚŠǕîOȄsȃɚɚOȄsȃɛɛǄĿƑƭƙɍ¹ĺĚȃȁȁȊOȂsȂƎîŠēĚŞĿČČîƭƙĚē ċǋĿŠǷƭĚŠǕîOȂsȂɚɚOȂsȂɛƎēŞȁȊɛǄĿƑƭƙĿƙĿŠēĿČîƥĚēċǋƥĺĚŕĿĳĺƥċŕƭĚîƑƑūǅɍ ƭƑƑĚŠƥŕǋɈɚOȄsȃɛ and A(H1N1)pdm09 viruses continue to cause epidemics.

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î ƙĚČūŠē ~¤G îČČĚƙƙĚē ǄĿî ƑĿċūƙūŞîŕ ĲƑîŞĚɠƙĺĿĲƥĿŠĳȅȅ_{îŠē ƥǅū sɠƥƑƭŠČîƥĚē ǄĚƑƙĿūŠƙ}

ūĲ¡ɒ¡ɠsȂȆȆîŠē¡ɠsȂȉȃȅȆ_{. The M and NS gene segments each encode a protein}

ĲƑūŞ ƥĺĚ ČūŕŕĿŠĚîƑ ƥƑîŠƙČƑĿƎƥ ɚqȂ îŠē s¬Ȃɛɍ ēēĿƥĿūŠîŕŕǋɈ ƥĺĚǋ ĚîČĺ ĚŠČūēĚ î ƙĚČūŠē ƎƑūƥĚĿŠ ƥĺƑūƭĳĺ Ş¤s ƙƎŕĿČĿŠĳ ɚqȃ îŠē s¬ȃɛɈ ƥĺĚ ŕîƥƥĚƑ ċĚĿŠĳ ċĚƥƥĚƑ ŒŠūǅŠ îƙ ƥĺĚ ŠƭČŕĚîƑĚǊƎūƑƥƎƑūƥĚĿŠɚs/¡ɛȅȇ_. ØĿƥĺĿŠƥĺĚǄĿƑƭƙƎîƑƥĿČŕĚɚGĿĳƭƑĚȃɛɈĚîČĺƙĚĳŞĚŠƥūĲŠĚĳîƥĿǄĚƙĚŠƙĚƙĿŠĳŕĚɠƙƥƑîŠēĚē ǄĿƑîŕ¤sɚǄ¤sɛĲūƑŞƙîƎîŠĺîŠēŕĚƙƥƑƭČƥƭƑĚƥĺƑūƭĳĺČūŞƎŕĚŞĚŠƥîƑĿƥǋūĲƥĺĚȆɫîŠē ȄɫƥĚƑŞĿŠĿɍ¹ĺĚ¤sĿƙƥĿĳĺƥŕǋƎîČŒĚēîƙîǄĿƑîŕƑĿċūŠƭČŕĚūƎƑūƥĚĿŠɚǄ¤s¡ɛċǋs¡îŠē ƥĺĚĺĚƥĚƑūƥƑĿŞĚƑĿČ¤sɠēĚƎĚŠēĚŠƥ¤sƎūŕǋŞĚƑîƙĚČūŞƎŕĚǊĲūƑƥĺĚƎƭƑƎūƙĚƙūĲ¤s GĿĳƭƑĚȃʯ¬ČĺĚŞîƥĿČēĿîĳƑîŞūĲĿŠǷƭĚŠǕîǄĿƑƭƙɍ¹ĺĚĿŠǷƭĚŠǕîǄĿƑƭƙƎîƑƥĿČŕĚČūŠƙĿƙƥƙūĲî

viral envelope and a viral core containing the eight-segmented genome. Three viral proteins are embedded in the host-derived lipid bilayer membrane: trimeric haemagglutinin (HA), tetrameric neuraminidase (NA), and tetrameric matrix protein M2 (ion-channel). Beneath the viral envelope resides the matrix, containing matrix protein M1, which provides rigidity and surrounds the eight viral ribonucleoproteins (vRNPs). The vRNPs are strands of negative sense single-stranded viral RNA (vRNA) molecules coated with nucleocapsid protein (NP) and attached to a heterotrimeric polymerase complex at the 5’ and 3’ termini. This polymerase complex consists of PB2, PB1, and PA. Since the vRNA in the vRNPs has complementary sequences at the 5’ and 3’ termini, the vRNA segments perform base pairing, forming a panhandle structure. Adapted from47_.

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ƥƑîŠƙČƑĿƎƥĿūŠɈƑĚƎŕĿČîƥĿūŠɈîŠēƎîČŒîĳĿŠĳɍ¹ĺĿƙƎūŕǋŞĚƑîƙĚČūŞƎŕĚǊČūŠƙĿƙƥƙūĲ¡ȃɈ¡ȂɈ îŠē¡ɍ¡ȂɠsȅȁŕîČŒƙƥƑîŠƙČƑĿƎƥîƙĚĲƭŠČƥĿūŠċƭƥēūĚƙĿŠƥĚƑîČƥǅĿƥĺƥĺĚƎūŕǋŞĚƑîƙĚ ČūŞƎŕĚǊ ĿŠ ƥĺĚ ČĚŕŕƭŕîƑ ĚŠǄĿƑūŠŞĚŠƥȅȃ_{Ɉ îŠē îŕƥĺūƭĳĺ ¡ɠsȂȆȆ îŠē ¡ɠsȂȉȃ ēū Šūƥ} ƙĺūǅƎūŕǋŞĚƑîƙĚîČƥĿǄĿƥǋɈŞƭƥîŠƥǄĿƑƭƙĚƙŕîČŒĿŠĳƥĺĚsɠƥƑƭŠČîƥĚē¡ƙƑĚƎŕĿČîƥĚǅĿƥĺ ŕūǅĚƑĚĲǶČĿĚŠČǋĿŠČĚŕŕČƭŕƥƭƑĚîŠēĺîǄĚƑĚēƭČĚēƎîƥĺūĳĚŠĿČĿƥǋĿŠŞĿČĚČūŞƎîƑĚēƥūƥĺĚ ǅĿŕēɠƥǋƎĚǄĿƑƭƙȅȆ_{ɍ¡ȂɠGȃɈ¡ɠÝɈîŠēēĿŞĚƑĿČs¬ȂîƑĚƭŠēĚƥĚČƥîċŕĚĿŠƥĺĚǄĿƑîŕƎîƑƥĿČŕĚ} îŠēîƑĚūŠŕǋĲūƭŠēĿŠĿŠĲĚČƥĚēČĚŕŕƙǅĺĚƑĚƥĺĚǋĿŠēƭČĚîƎūƎƥūƙĿƙɚ¡ȂɠGȃɛɈŞūēƭŕîƥĚ ĺūƙƥƑĚƙƎūŠƙĚîŠēǄĿƑîŕǄĿƑƭŕĚŠČĚɚ¡ɠÝɛɈîŕŕūǅĚƙČîƎĚĲƑūŞîŠƥĿǄĿƑîŕŞĚČĺîŠĿƙŞƙɚs¬ȂɛɈ ūƑƑĚĳƭŕîƥĚĳĚŠĚĚǊƎƑĚƙƙĿūŠɚs¬Ȃɛȅȉ_{. Besides the eight vRNPs, NEP is found within the}

ǄĿƑîŕƎîƑƥĿČŕĚîŠēɈîŕūŠĳǅĿƥĺqȂɈēĿƑĚČƥƙƥĺĚŠƭČŕĚîƑĚǊƎūƑƥūĲƥĺĚǄ¤s¡ƙɍqȂƎƑūƥĚĿŠƙ ĲūƑŞîŕîǋĚƑƎƑūǄĿēĿŠĳƑĿĳĿēĿƥǋƥūƥĺĚǄĿƑƭƙƎîƑƥĿČŕĚɈǅĺĿČĺƭŠēĚƑŕĿĚƙƥĺĚĺūƙƥɠēĚƑĿǄĚēŕĿƎĿē ċĿŕîǋĚƑŞĚŞċƑîŠĚɍ¹ĺƑĚĚǄĿƑîŕƎƑūƥĚĿŠƙɜOɈsɈîŠēqȃɜîƑĚĚŞċĚēēĚēĿŠƥĺĚŕĿƎĿē ċĿŕîǋĚƑŞĚŞċƑîŠĚɍOĿƙîĺūŞūƥƑĿŞĚƑĿČƥǋƎĚTĿŠƥĚĳƑîŕŞĚŞċƑîŠĚƎƑūƥĚĿŠūĲǅĺĿČĺĚîČĺ ŞūŠūŞĚƑČūŠƥîĿŠƙîƑĚČĚƎƥūƑċĿŠēĿŠĳƙĿƥĚɚ¤¬ɛɍ¹ĺĚƎƑĚČƭƑƙūƑOŞūŕĚČƭŕĚɜOȁɜĿƙ ƎƑūƥĚūŕǋƥĿČîŕŕǋČŕĚîǄĚēĿŠƥūOȂîŠēOȃƙƭċƭŠĿƥƙȅȊ_{ƥūîČƥĿǄîƥĚǄĿƑƭƙĿŠĲĚČƥĿǄĿƥǋ}ȆȁɈȆȂ_ɍOȂ ĿƙƥĺĚĿŞŞƭŠūĳĚŠĿČƙĚČƥĿūŠūĲƥĺĚOƎƑūƥĚĿŠȆȃɈȆȄ_{ɈîŠēOȃČūŠƥîĿŠƙîĲƭƙĿūŠēūŞîĿŠ}Ȇȅ_. sĿƙîƥĚƥƑîŞĚƑĿČƥǋƎĚTTĿŠƥĚĳƑîŕŞĚŞċƑîŠĚƎƑūƥĚĿŠƎūƙƙĚƙƙĿŠĳƙĿîŕĿēîƙĚîČƥĿǄĿƥǋɍqȃɜî ƥĚƥƑîŞĚƑĿČƥǋƎĚTTTĿŠƥĚĳƑîŕŞĚŞċƑîŠĚƎƑūƥĚĿŠɜĺîƙĿūŠČĺîŠŠĚŕîČƥĿǄĿƥǋîŕŕūǅĿŠĳƎƑūƥūŠƙ ĲƑūŞƥĺĚîČĿēĿǶĚēĚŠēūƙūŞĚƙĿŠƥūƥĺĚǄĿƑƭƙƎîƑƥĿČŕĚƥūƙĚƎîƑîƥĚƥĺĚǄ¤s¡ƙĲƑūŞqȂɍ ¤ĚƎŕĿČîƥĿūŠČǋČŕĚ ¤ĚƙƎĿƑîƥūƑǋ ēƑūƎŕĚƥƙ ūƑ îĚƑūƙūŕƙ ŕūîēĚē ǅĿƥĺ ǄĿƑƭƙ îƑĚ ƑĚŕĚîƙĚē ēƭƑĿŠĳ ċƑĚîƥĺĿŠĳɈ ČūƭĳĺĿŠĳɈ îŠē ƙŠĚĚǕĿŠĳ ċǋ îŠ ĿŠĲĚČƥĚē ĿŠēĿǄĿēƭîŕȆȆɝȆȈ_{. The droplets or aerosols enter}

ƥĺĚ ƑĚƙƎĿƑîƥūƑǋ ƥƑîČƥ ūĲ îŠūƥĺĚƑ ĿŠēĿǄĿēƭîŕ ǅĺĚƑĚ ƥĺĚ T× ċĿŠēƙ ƥū ƥĚƑŞĿŠîŕ ƙĿîŕĿČ îČĿēɠČūŠƥîĿŠĿŠĳƑĚČĚƎƥūƑƙūŠƥĺĚĚƎĿƥĺĚŕĿîŕČĚŕŕƙƭƑĲîČĚƥĺƑūƭĳĺƥĺĚO¤¬Ȇȉ_{, enabling}

ĚŠƥƑîŠČĚ ƥĺƑūƭĳĺ ĿŠƥĚƑŠîŕĿǕîƥĿūŠ ĿŠƥū ĚŠēūƙūŞĚƙ ċǋ ƑĚČĚƎƥūƑ ŞĚēĿîƥĚē ĚŠēūČǋƥūƙĿƙɍ ¹ĺĚ ĿūŠ ČĺîŠŠĚŕ îČƥĿǄĿƥǋ ūĲ qȃ Ŀƙ îČƥĿǄîƥĚēɈ ċǋ ǅĺĿČĺ ĿūŠƙ Ƿūǅ ĲƑūŞ ƥĺĚ îČĿēĿǶĚē endosome to the virion interiorȆȊ_{. The acidic environment triggers a conformational}

ČĺîŠĳĚ ūĲ ƥĺĚ ČŕĚîǄĚē OɈ ĚǊƎūƙĿŠĳ ƥĺĚ ĲƭƙĿūŠ ƎĚƎƥĿēĚ îƥ ƥĺĚ sɠƥĚƑŞĿŠƭƙ ūĲ ƥĺĚ Oȃ ƙƭċƭŠĿƥȇȁ_{. This allows fusion of the viral membrane with the cellular membrane}

ƑĚƙƭŕƥĿŠĳ ĿŠ ƥĺĚ ƑĚŕĚîƙĚ ūĲ ƥĺĚ ĚĿĳĺƥ Ǆ¤s¡ƙ ĿŠƥū ƥĺĚ ČǋƥūƎŕîƙŞɍ ¹ĺĚ ĿŠƥîČƥ Ǆ¤s¡ƙ îƑĚ îČƥĿǄĚŕǋ ĿŞƎūƑƥĚē ĿŠƥū ƥĺĚ ŠƭČŕĚƭƙ ƥĺƑūƭĳĺ ƥĺĚ ŠƭČŕĚîƑ ƎūƑĚɈ ƙĿŠČĚ îŕŕ ƎƑūƥĚĿŠƙ ūĲ ƥĺĚ Ǆ¤s¡ɜ¡ȃɈ ¡ȂɈ ¡Ɉ îŠēɈ ƎîƑƥĿČƭŕîƑŕǋɈ s¡ɜČūŠƥîĿŠ ŠƭČŕĚîƑ ŕūČîŕĿǕîƥĿūŠ ƙĿĳŠîŕƙȇȂ_{ɍ TŠ}

ƥĺĚ ŠƭČŕĚƭƙɈ ƥĺĚ ƎūŕǋŞĚƑîƙĚ ČūŞƎŕĚǊ ƥƑîŠƙČƑĿċĚƙ ƥĺĚ Ǆ¤sƙ ĿŠƥū Ş¤sƙɍ TŠĿƥĿîƥĿūŠ ūĲ ĿŠǷƭĚŠǕî Ş¤s ƑĚƐƭĿƑĚƙ ČîƎƎĚē ƎƑĿŞĚƑƙ ĳĚŠĚƑîƥĚē ĲƑūŞ ƥĺĚ ĺūƙƥ ČĚŕŕƭŕîƑ Ş¤s

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GĿĳƭƑĚȄʯ¹ĺĚƑĚƎŕĿČîƥĿūŠČǋČŕĚūĲĿŠǷƭĚŠǕîǄĿƑƭƙɍ Upon binding to sialic acid receptors on the

ĚƎĿƥĺĚŕĿîŕČĚŕŕƙƭƑĲîČĚǄĿîƥĺĚĺîĚŞîĳĳŕƭƥĿŠĿŠɚOɛĳŕǋČūƎƑūƥĚĿŠɈƥĺĚĿŠǷƭĚŠǕîǄĿƑƭƙĿƙĿŠƥĚƑŠîŕĿǕĚē into endosomes by receptor mediated endocytosis. Hereafter, the ion channel activity of matrix ƎƑūƥĚĿŠȃɚqȃɛĿƙîČƥĿǄîƥĚēɈċǋǅĺĿČĺĿūŠƙǷūǅĲƑūŞƥĺĚĚŠēūƙūŞĚƥūƥĺĚǄĿƑĿūŠĿŠƥĚƑĿūƑɍ¹ĺĚŕūǅ pH in the endosome triggers fusion of the viral and endosomal membranes, releasing the viral ribonucleoproteins (vRNPs) into the cytoplasm. The intact vRNPs are actively imported into the nucleus through the nuclear pore. In the nucleus, the polymerase complex transcribes the viral RNAs (vRNAs) into mRNAs. After synthesis of the mRNAs in the nucleus, the mRNAs are translated within the cytoplasm, yielding viral proteins. Newly formed proteins are either transported back into the nucleus or transported to the cell membrane. The vRNA serves additionally as a template for synthesis of complementary RNA (cRNA). This cRNA is positive stranded and needed as a template for the synthesis of vRNA. The vRNA is exported from the nucleus, together with newly synthesized viral proteins, as vRNP complexes. The vRNPs are then packaged, leading to the assembly of progeny virus. This is realized by means of ‘budding’, in which the lipid membrane of the host cell serves as the viral envelope. The sialic acids are enzymatically removed by neuraminidase (NA), resulting in the release of the virion from the cell. Adapted from70_.

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ċǋƥĺĚČîƎɠēĚƎĚŠēĚŠƥĚŠēūŠƭČŕĚîƙĚîČƥĿǄĿƥǋūĲ¡ȃȇȃ_{ɍĲƥĚƑƙǋŠƥĺĚƙĿƙĿŠƥĺĚŠƭČŕĚƭƙɈ} ƥĺĚŞ¤sƙîƑĚƥƑîŠƙŕîƥĚēǅĿƥĺĿŠƥĺĚČǋƥūƎŕîƙŞɈǋĿĚŕēĿŠĳǄĿƑîŕƎƑūƥĚĿŠƙɍsĚǅŕǋĲūƑŞĚē ƎƑūƥĚĿŠƙîƑĚĚĿƥĺĚƑƥƑîŠƙƎūƑƥĚēċîČŒĿŠƥūƥĺĚŠƭČŕĚƭƙɚ¡ȃɈ¡ȂɈ¡Ɉs¡ɈqȂɈîŠēs/¡ɛ ūƑƥƑîŠƙƎūƑƥĚēƥūƥĺĚČĚŕŕŞĚŞċƑîŠĚɚOɈsɈîŠēqȃɛȅɈȇ_{ɍ¹ĺĚǄ¤sîēēĿƥĿūŠîŕŕǋƙĚƑǄĚƙ} îƙ î ƥĚŞƎŕîƥĚ ĲūƑ ƙǋŠƥĺĚƙĿƙ ūĲ ČūŞƎŕĚŞĚŠƥîƑǋ ¤s ɚČ¤sɛȇ_{ɍ ¹ĺĿƙ Č¤s Ŀƙ ƎūƙĿƥĿǄĚ} ƙƥƑîŠēĚē îŠē ŠĚĚēĚē îƙ î ƥĚŞƎŕîƥĚ ĲūƑ ƥĺĚ ƙǋŠƥĺĚƙĿƙ ūĲ Ǆ¤sȇ_{ɍ s/¡ îŠē qȂ ĚŠîċŕĚ} ƥĺĚĚǊƎūƑƥūĲǄ¤sĲƑūŞƥĺĚŠƭČŕĚƭƙɈƥūĳĚƥĺĚƑǅĿƥĺŠĚǅŕǋƙǋŠƥĺĚƙĿǕĚēǄĿƑîŕƎƑūƥĚĿŠƙɈ îƙ Ǆ¤s¡ ČūŞƎŕĚǊĚƙȅȇɈȇȄɈȇȅ_{ɍ ¹ĺĚ Ǆ¤s¡ƙ îƑĚ ƥĺĚŠ ƎîČŒîĳĚēɈ ŕĚîēĿŠĳ ƥū ƥĺĚ îƙƙĚŞċŕǋ ūĲ} ƎƑūĳĚŠǋǄĿƑƭƙɍ¹ĺĿƙĿƙƑĚîŕĿǕĚēċǋŞĚîŠƙūĲɪċƭēēĿŠĳɫɈĿŠǅĺĿČĺƥĺĚŕĿƎĿēŞĚŞċƑîŠĚūĲ the host cell serves as the viral envelopeȇȆ_{ɍ¹ĺĚƥĚƑŞĿŠîŕƙĿîŕĿČîČĿēƙîƑĚĚŠǕǋŞîƥĿČîŕŕǋ}

ƑĚŞūǄĚēċǋsɈƑĚƙƭŕƥĿŠĳĿŠƥĺĚƑĚŕĚîƙĚūĲƥĺĚǄĿƑĿūŠĲƑūŞƥĺĚČĚŕŕȇȇɝȇȊ_{ɚGĿĳƭƑĚȈîɛɍ¹ĺĿƙ}

îČƥĿǄĿƥǋîŕƙūƎƑĚǄĚŠƥƙîĳĳƑĚĳîƥĿūŠūĲǄĿƑĿūŠƙȇȉ_.

¤ĚîƙƙūƑƥŞĚŠƥ

¹ĺĚƙĚĳŞĚŠƥĚēŠîƥƭƑĚūĲƥĺĚĿŠǷƭĚŠǕîǄĿƑƭƙĳĚŠūŞĚîŕŕūǅƙĲūƑƥĺĚĚǊČĺîŠĳĚūĲĚŠƥĿƑĚ ĳĚŠĚƙċĚƥǅĚĚŠēĿĲĲĚƑĚŠƥĿŠǷƭĚŠǕîǄĿƑƭƙĚƙēƭƑĿŠĳƙĿŞƭŕƥîŠĚūƭƙČūɠĿŠĲĚČƥĿūŠūĲîĺūƙƥɈ in a process called reassortmentȅ_{ɚGĿĳƭƑĚȅɛɍƥŕĚîƙƥūŠĚČūƎǋūĲĚîČĺĳĚŠĚƙĚĳŞĚŠƥ}

Ŀƙ ŠĚĚēĚē ĲūƑ îŠ ĿŠǷƭĚŠǕî ǄĿƑƭƙ ƎîƑƥĿČŕĚ ƥū ċĚ ĿŠĲĚČƥĿūƭƙȅ_{, and this incorporation}

mechanism is selectiveȈȂɈȈȃ_{ɍ /ŕĚČƥƑūŠ ŞĿČƑūƙČūƎǋ ƙƥƭēĿĚƙ ƙĺūǅ î ĺĿĳĺŕǋ ūƑĳîŠĿǕĚē} ƙƥƑƭČƥƭƑĚǅĿƥĺĿŠĿŠǷƭĚŠǕîǄĿƑĿūŠƙɈČūŞƎƑĿƙĿŠĳūŠĚČĚŠƥƑîŕǄ¤s¡ƙƭƑƑūƭŠēĚēċǋƙĚǄĚŠ ūƥĺĚƑƙūĲǄîƑǋĿŠĳŕĚŠĳƥĺȈȄɝȈȆ_{ɈîŠēƙĚĳŞĚŠƥɠƙƎĚČĿǶČƎîČŒîĳĿŠĳƙĿĳŠîŕƙŕūČîƥĚēîƥƥĺĚȆɫ} îŠēȄɫĚŠēūĲƥĺĚČūēĿŠĳƑĚĳĿūŠƙĺîǄĚċĚĚŠēĚǶŠĚēȈȂɈȈȃɈȈȇɝȉȄ_. TŠƥĚƑƙƭċƥǋƎĿČ ƑĚîƙƙūƑƥŞĚŠƥƙ ċĚƥǅĚĚŠ ƙǅĿŠĚɈ îǄĿîŠɈ îŠēɓūƑ ĺƭŞîŠ T× ĺîǄĚ ŕĚēƥūƙĚǄĚƑîŕƎîŠēĚŞĿČƙɍ¹ĺĚȂȊȆȈɠȂȊȆȉƎîŠēĚŞĿČɚOȃsȃɛǄĿƑƭƙǅîƙƥĺĚƑĚƙƭŕƥūĲ ƑĚîƙƙūƑƥŞĚŠƥċĚƥǅĚĚŠƥĺĚîƥƥĺĚƥĿŞĚɠČĿƑČƭŕîƥĿŠĳƙĚîƙūŠîŕĿŠǷƭĚŠǕîɚOȂsȂɛǄĿƑƭƙîŠē îŠîǄĿîŠĿŠǷƭĚŠǕîɚOȃsȃɛǄĿƑƭƙȉȅ_{ĲƑūŞǅĺĿČĺĿƥēĚƑĿǄĚēƥĺĚOɈsîŠē¡Ȃɍ¹ĺĚȂȊȇȉ} ƎîŠēĚŞĿČɚOȄsȃɛǄĿƑƭƙǅîƙƥĺĚƑĚƙƭŕƥūĲƑĚîƙƙūƑƥŞĚŠƥċĚƥǅĚĚŠîĺƭŞîŠɚOȃsȃɛǄĿƑƭƙ ǅĿƥĺîŠîǄĿîŠOȄǄĿƑƭƙȉȅ_{ūĲǅĺĿČĺƥĺĚŕîƥƥĚƑƎƑūǄĿēĚēƥĺĚOîŠē¡ȂƎƑūƥĚĿŠƙɍĚƥǅĚĚŠ} ȂȊȈȈîŠēȃȁȁȊɈūČČîƙĿūŠîŕƑĚîƙƙūƑƥîŠƥƙċĚƥǅĚĚŠČūŠƥĚŞƎūƑîƑǋĺƭŞîŠɚOȂsȂɛîŠē ɚOȄsȃɛǄĿƑƭƙĚƙĺîǄĚċĚĚŠēĚƥĚČƥĚēȄȂɈȉȆɝȊȄ_{, but these have never persisted as seasonal}

ĿŠǷƭĚŠǕîɍ¹ĺĚȃȁȁȊOȂsȂƎîŠēĚŞĿČǅîƙƥĺĚƎƑūēƭČƥūĲƑĚîƙƙūƑƥŞĚŠƥĿŠǅĺĿČĺƥĺĚs îŠēqĳĚŠĚƙǅĚƑĚēĚƑĿǄĚēĲƑūŞî/ƭƑîƙĿîŠîǄĿîŠɡŕĿŒĚƙǅĿŠĚǄĿƑƭƙɈîŠēƥĺĚƑĚŞîĿŠĿŠĳƙĿǊ gene segments were derived from triple reassortant swine viruses that possessed genes ūƑĿĳĿŠîƥĿŠĳĲƑūŞČŕîƙƙĿČîŕɚOȂsȂɛƙǅĿŠĚɈsūƑƥĺŞĚƑĿČîŠîǄĿîŠɈîŠēĺƭŞîŠɚOȄsȃɛ virusesȊȅ_{ɍ¤ĚîƙƙūƑƥŞĚŠƥċĚƥǅĚĚŠT×ūĲƥĺĚƙîŞĚƙƭċƥǋƎĚɈĿŠƥƑîƙƭċƥǋƎĿČƑĚîƙƙūƑƥŞĚŠƥɈĿƙ}

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ŞūƙƥŕĿŒĚŕǋūŠĚūĲŞîŠǋǅîǋƙĲūƑƥĺĚǄĿƑƭƙƥūĿŠČƑĚîƙĚēĿǄĚƑƙĿƥǋȊȆɝȂȁȁ_{, including producing}

ǄîƑĿîŠƥƙǅĿƥĺĚŠĺîŠČĚēƥƑîŠƙŞĿƙƙĿċĿŕĿƥǋȂȁȂ_{, and those that are resistant to antiviral drugs}Ȃȁȃ_.

Genetic and antigenic evoluti on

ĺîŕŕŞîƑŒūĲ¤sǄĿƑƭƙĚƙĿƙƥĺĚĿƑĺĿĳĺĳĚŠūŞĚŞƭƥîƥĿūŠĲƑĚƐƭĚŠČǋɍ¹ĺĚĿŠǷƭĚŠǕîǄĿƑƭƙ ƎūŕǋŞĚƑîƙĚ ŕîČŒƙ ƎƑūūĲƑĚîēĿŠĳ ČîƎîČĿƥǋɈ ŕĚîēĿŠĳ ƥū îŠ ĚŠūƑŞūƭƙ ǄîƑĿĚƥǋ ūĲ ƎƑūĳĚŠǋ ǄĿƑƭƙĚƙɍ¹ĺĚŞîŏūƑĿƥǋūĲƥĺĚƙĚŞƭƥîƥĿūŠƙČūŠƥƑĿċƭƥĚƥūƥĺĚŠĚƭƥƑîŕƙĚƐƭĚŠČĚĚǄūŕƭƥĿūŠȊȊ_, îŕƙūŒŠūǅŠîƙĳĚŠĚƥĿČēƑĿĲƥɍOūǅĚǄĚƑɈƙūŞĚūĲƥĺĚƎƑūĳĚŠǋŞƭƥîŠƥǄĿƑƭƙĚƙɈĿŠƎîƑƥĿČƭŕîƑ ƭŠēĚƑ ƙĚŕĚČƥĿǄĚ ČūŠēĿƥĿūŠƙɈ ĺîǄĚ îēǄîŠƥîĳĚūƭƙ ČĺîƑîČƥĚƑĿƙƥĿČƙ îŠē îƑĚ ƥĺƭƙ ƑîƎĿēŕǋ îŞƎŕĿǶĚēɍ¹ĺĿƙƎƑūČĚƙƙūĲŠîƥƭƑîŕƙĚŕĚČƥĿūŠîČƥƙūŠɠČĚŕŕȂȁȄ_{îŠē¹ɠČĚŕŕĚƎĿƥūƎĚƙ}Ȃȁȅ_{, aids}

in drug resistance, and enables propagation under altered growth conditionsȂȁȄ_.

qƭƥîƥĿūŠƙƥĺîƥîƑĿƙĚēƭƑĿŠĳîŠƥĿċūēǋŞĚēĿîƥĚēƙĚŕĚČƥĿūŠɈŕĚîēĿŠĳƥūîŕƥĚƑîƥĿūŠƙ ĿŠƥĺĚŞîŏūƑƙƭƑĲîČĚĳŕǋČūƎƑūƥĚĿŠƙɈČîŠƑĚƙƭŕƥĿŠɪîŠƥĿĳĚŠĿČēƑĿĲƥɫȂȁȆ_{ɍŠƥĿċūēĿĚƙĚŕĿČĿƥĚē}

ƥūƥĺĚɪūƑĿĳĿŠîŕɫǄĿƑƭƙŞîǋŕūƙĚƥĺĚîċĿŕĿƥǋƥūƑĚČūĳŠĿǕĚƥĺĚǄĿƑƭƙūƑĺîǄĚƑĚēƭČĚēîĲǶŠĿƥǋɈ ƑĚƙƭŕƥĿŠĳĿŠĿŠĲĚČƥĿūŠūĲƥĺĚĺūƙƥɍŠƥĿĳĚŠĿČēƑĿĲƥĿŠČƑĚîƙĚƙēĿǄĚƑƙĿƥǋċƭƥɈŞūƑĚĿŞƎūƑƥîŠƥŕǋɈ GĿĳƭƑĚ ȅ ʯ TŠǷƭĚŠǕî ǄĿƑƭƙ ƑĚîƙƙūƑƥŞĚŠƥɍ Two virus particles are shown, each with a full

complement of eight viral genome segments. Following reassortment, hybrid progeny can be formed that contain segments derived from both parents. Adapted from4_.

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GĿĳƭƑĚȆʯŠƥĿĳĚŠĿČŞîƎūĲĿŠǷƭĚŠǕîɚOȄsȃɛǄĿƑƭƙĲƑūŞȂȊȇȉƥūȃȁȁȄɍThe distance between

antiserum (uncoloured open shapes) point S and virus (antigen, coloured shapes) point A corresponds to the difference between the base 2 logarithm (log₂) of the maximum titre for antiserum S against any antigen and the log2 of the titre for antiserum S against antigen A. Consequently, each titre in

an haemagglutination inhibition (HI) table can be thought of as specifying the ideal target distance ċĚƥǅĚĚŠƥĺĚîŠƥĿƙĚƑƭŞîŠēîŠƥĿĳĚŠƎūĿŠƥƙĿŠƥĺĚƑĚƙƭŕƥĿŠĳîŠƥĿĳĚŠĿČŞîƎɍqūēĿǶĚēŞƭŕƥĿēĿŞĚŠƙĿūŠîŕ scaling (MDS) methods are used to arrange the antigen and antiserum points in an antigenic map

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ĿƙîǅîǋĲūƑƥĺĚǄĿƑƭƙƥūĚĲĲĚČƥĿǄĚŕǋĚǄîēĚƥĺĚĺūƙƥɫƙĿŞŞƭŠĚƙǋƙƥĚŞîŠēĿƙƑĚƙƎūŠƙĿċŕĚ ĲūƑƥĺĚƑĚČƭƑƑĚŠČĚūĲĿŠǷƭĚŠǕîĚƎĿēĚŞĿČƙîŕŞūƙƥĚǄĚƑǋǅĿŠƥĚƑɍ OĿƑƙƥǅîƙƥĺĚǶƑƙƥƥūēĿƙČūǄĚƑƥĺĚîĳĳŕƭƥĿŠîƥĿūŠūĲƑĚēċŕūūēČĚŕŕƙċǋƥĺĚĿŠǷƭĚŠǕî virusȂȁȇ_{ɍ¹ĺĿƙîĳĳŕƭƥĿŠîƥĿūŠĿƙƥĺĚċîƙĿƙūĲƥĺĚĺîĚŞîĳĳŕƭƥĿŠîƥĿūŠĿŠĺĿċĿƥĿūŠɚOTɛîƙƙîǋ} ǅĺĿČĺČîŠċĚƭƙĚēƥūēĚƥĚČƥîŠƥĿĳĚŠĿČēĿĲĲĚƑĚŠČĚƙĿŠOɍTŠƥĺĚOTîƙƙîǋɈƥĺĚƎƑĚƙĚŠČĚ ūĲOƙƎĚČĿǶČîŠƥĿċūēĿĚƙĿŠîŠƥĿƙĚƑîƎƑĚǄĚŠƥƥĺĚċĿŠēĿŠĳūĲOƥūƙĿîŕĿČîČĿēČūŠƥîĿŠĿŠĳ receptors present on red blood cells, thus preventing the agglutination of red blood cells. ¹ĺĚîŞūƭŠƥūĲĿŠĺĿċĿƥĿūŠċǋîŠƥĿƙĚƑîĿƙČūŠǄĚƑƥĚēĿŠƥūîŠOTƥĿƥƑĚɍTŠȃȁȁȅɈ¬ŞĿƥĺĚƥîŕɍ ēĚƙĿĳŠĚēɪîŠƥĿĳĚŠĿČČîƑƥūĳƑîƎĺǋɫɈîƥūūŕƥūǄĿƙƭîŕĿǕĚîŠēƐƭîŠƥĿĲǋƥĺĚƙĚOTēîƥîȂȁȈ_{. With this}

ƥūūŕƥĺĚîŠƥĿĳĚŠĿČĚǄūŕƭƥĿūŠūĲƥĺĚOƎƑūƥĚĿŠƙūĲɚOȄsȃɛǄĿƑƭƙĚƙǅîƙŞîƎƎĚēɈĲƑūŞƥĺĚĿƑ ĿŠƥƑūēƭČƥĿūŠĿŠƥūĺƭŞîŠƙĿŠȂȊȇȉƭŠƥĿŕȃȁȁȄɚGĿĳƭƑĚȆɛɍ¹ĺĚƙƥƭēǋƑĚǄĚîŕĚēîƎƭŠČƥƭîƥĚē ƎîƥƥĚƑŠūĲĚŕĚǄĚŠîŠƥĿĳĚŠĿČČŕƭƙƥĚƑƙɈŠîŞĚēîĲƥĚƑƥĺĚǶƑƙƥǄîČČĿŠĚƙƥƑîĿŠĿŠƥĺĚČŕƭƙƥĚƑɒ OūŠĳeūŠĳȂȊȇȉɈ/ŠĳŕîŠēȂȊȈȃɈ×ĿČƥūƑĿîȂȊȈȆɈ¹ĚǊîƙȂȊȈȈɈîŠĳŒūŒȂȊȈȊɈ¬ĿČĺƭîŠ ȂȊȉȈɈĚĿŏĿŠĳȂȊȉȊɈĚĿŏĿŠĳȂȊȊȃɈØƭĺîŠȂȊȊȆɈ¬ǋēŠĚǋȂȊȊȈɈîŠēGƭŏĿîŠȃȁȁȃɍ/îČĺūĲ ƥĺĚƙĚîŠƥĿĳĚŠĿČČŕƭƙƥĚƑƙČūŠƥîĿŠƙǄĿƑƭƙĚƙƥĺîƥîƑĚîŠƥĿĳĚŠĿČîŕŕǋƙĿŞĿŕîƑĲūƑƙūŞĚƥĿŞĚɈîĲƥĚƑ ǅĺĿČĺƥĺĚƙĚǄĿƑƭƙĚƙČĺîŠĳĚîŠƥĿĳĚŠĿČîŕŕǋɈƑĚƙƭŕƥĿŠĳĿŠîɨČŕƭƙƥĚƑƥƑîŠƙĿƥĿūŠɩɍ¹ĺĚƙĚČŕƭƙƥĚƑ ƥƑîŠƙĿƥĿūŠƙǅîƑƑîŠƥîƥŕĚîƙƥūŠĚǄîČČĿŠĚƭƎēîƥĚɍŠƥĿĳĚŠĿČČŕƭƙƥĚƑƙƑĚŞîĿŠēūŞĿŠîŠƥĲūƑūŠ îǄĚƑîĳĚȄɍȄǋĚîƑƙɈîŠēƙƥƑîĿŠƙîƎƎĚîƑĚēƭƎƥūȃǋĚîƑƙċĚĲūƑĚîŠēƭŠƥĿŕȃǋĚîƑƙîĲƥĚƑƥĺĚ ƎĚƑĿūēĿŠǅĺĿČĺƥĺîƥČŕƭƙƥĚƑĿƙēūŞĿŠîŠƥɍ¹ĺĚƙĚČŕƭƙƥĚƑƙǅĚƑĚƙūŞĚǅĺîƥŕĿŠĚîƑŕǋîŕĿĳŠĚēɈ îŠēĿƥǅîƙĺǋƎūƥĺĚƙĿǕĚēƥĺîƥŠĚǅČŕƭƙƥĚƑƙƥĚŠēƥūŞūǄĚîǅîǋîƙĲîƑîƙƎūƙƙĿċŕĚĲƑūŞƥĺĚ ƎƑĚǄĿūƭƙČŕƭƙƥĚƑɈƥĺĚƑĚċǋŞūƙƥĚĲĲĚČƥĿǄĚŕǋĚƙČîƎĿŠĳĚǊĿƙƥĿŠĳƎūƎƭŕîƥĿūŠɠŕĚǄĚŕĿŞŞƭŠĿƥǋȂȁȈ_. sĚƭƑîŞĿŠĿēîƙĚ ¹ĺĚ ƑĚČĚƎƥūƑɠēĚƙƥƑūǋĿŠĳ îČƥĿǄĿƥǋ ūĲ ĿŠǷƭĚŠǕî ǄĿƑƭƙ ǅîƙ ǶƑƙƥ ūċƙĚƑǄĚē ċǋ OĿƑƙƥȂȁȇ ĿŠ ȂȊȅȂɈ îŠē ƥĺĚ ƎƑūēƭČƥ ƥĺîƥ ǅîƙ ČŕĚîǄĚē ǅîƙ ĿēĚŠƥĿǶĚē ċǋ HūƥƥƙČĺîŕŒ ĿŠ ȂȊȆȇ îƙ sɠîČĚƥǋŕŠĚƭƑîŞĿŠĿČ îČĿēɈ ūŠĚ ūĲ ƥĺĚ ƙĿîŕĿČ îČĿēƙȂȁȉ_{ɍ ¹ĺĿƙ ŕĚē ƥū ƥĺĚ ēĿƙČūǄĚƑǋ ūĲ ƥĺĚ} ƙĚČūŠē ŞîŏūƑ ƙƭƑĲîČĚ ĳŕǋČūƎƑūƥĚĿŠ ɪsɫ ĿŠ ȂȊȆȈ ċǋ HūƥƥƙČĺîŕŒɈ ǅĺū ƙĺūǅĚē ƥĺîƥ s ƙƎŕĿƥūĲĲƥĺĚƥĚƑŞĿŠîŕŠĚƭƑîŞĿŠĿČîČĿēƭŠĿƥĲƑūŞĿŠĺĿċĿƥūƑǋŞƭČūƎƑūƥĚĿŠƙîŠēĿŠĺĿċĿƥūƑǋ ĳŕǋČūŕĿƎĿēƙȇȊ_{ɍTŠȂȊȇȅɈĿƥǅîƙƙĺūǅŠƥĺîƥƥĺĚsîŠēOîČƥĿǄĿƥĿĚƙƑĚƙĿēĚūŠēĿĲĲĚƑĚŠƥ} proteinsȂȁȊ_{ɍ ¹ĺĚ s ūĲ Şūƙƥ T× ƙƭċƥǋƎĚƙ îŠē ūĲ T× ĺîƙ ċĚĚŠ ČƑǋƙƥîŕŕĿǕĚē}ȂȂȁɝȂȂȉ_, îŕŕūǅĿŠĳ ƙƥƭēǋ ūĲ Ŀƥƙ ƥĺƑĚĚɠēĿŞĚŠƙĿūŠîŕ ƙƥƑƭČƥƭƑĚɍ ¹ĺĚ ƥĺƑĚĚɠēĿŞĚŠƙĿūŠîŕ ƙƥƑƭČƥƭƑĚ ūĲ s ČūŠƙĿƙƥƙ ūĲ ĲūƭƑ ēūŞîĿŠƙɇ ƥĺĚ ČǋƥūƎŕîƙŞĿČɈ ƥƑîŠƙŞĚŞċƑîŠĚɈ ƙƥîŕŒɈ îŠē ĺĚîēɍ s Ŀƙ î ŞƭƙĺƑūūŞɠƙĺîƎĚē ƥĚƥƑîŞĚƑĿČ ƎƑūƥĚĿŠȂȂȊ_{Ɉ îŠē ūŠĚ ǄĿƑîŕ ƎîƑƥĿČŕĚ ĺîƙ îƎƎƑūǊĿŞîƥĚŕǋ} ƥĺĿƑƥǋ ƥū ĲūƑƥǋ s ƥĚƥƑîŞĚƑƙɈ ĲūƑŞĚē ĿŠƥū ČŕƭƙƥĚƑƙɈ îŞūŠĳ ȃȊȁɠȄȁȁ O ƙƎĿŒĚƙ ūŠ îŠ îǄĚƑîĳĚɠƙĿǕĚē ǄĿƑĿūŠȈȄ_{. Each identical subunit of the tetrameric protein carries the}

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ĚŠǕǋŞĚɫƙîČƥĿǄĚƙĿƥĚɍOūǅĚǄĚƑɈƥĺĚŞūŠūŞĚƑĿČĲūƑŞūĲsĺîƙŠūĚŠǕǋŞĚîČƥĿǄĿƥǋȂȃȁɈȂȃȂ_.

¹ĺĚsîČƥĿǄĚƙĿƥĚĿƙîƙĺîŕŕūǅƎūČŒĚƥŕĿŠĚēċǋČūŠƙĚƑǄĚēîŞĿŠūîČĿēƑĚƙĿēƭĚƙɈƙūŞĚ ūĲǅĺĿČĺċĿŠēēĿƑĚČƥŕǋƥūƥĺĚǄĿƑîŕƑĚČĚƎƥūƑƙĿîŕĿČîČĿēîŠēƎîƑƥĿČĿƎîƥĚĿŠČîƥîŕǋƙĿƙɈǅĺĿŕĚ others provide a structural frameworkȂȂȊ_{ɚGĿĳƭƑĚȇɛɍ}

ŠƥĿĳĚŠĿČēƑĿĲƥĺîƙċĚĚŠƙƥƭēĿĚēŞūƙƥČūŠƙĿēĚƑîċŕǋĲūƑOɈĚǄĚŠƥĺūƭĳĺsĺîƙ also been observed to undergo antigenic driftȂȃȃɝȂȃȅ_{ɍsɠƙƎĚČĿǶČîŠƥĿċūēĿĚƙČîŠƑĚēƭČĚ}

ǄĿƑîŕƑĚƎŕĿČîƥĿūŠîŠēēĿƙĚîƙĚƙĚǄĚƑĿƥǋĿŠŞĿČĚȂȃȆ_{and chickens}Ȃȃȇ_{ɈîŠēĺîǄĚƙĿŞĿŕîƑŕǋċĚĚŠ} îƙƙūČĿîƥĚēǅĿƥĺƑĚƙĿƙƥîŠČĚîĳîĿŠƙƥĿŠǷƭĚŠǕîĿŠĺƭŞîŠƙȂȃȈɈȂȃȉ_{ɍŕƥĺūƭĳĺîŠƥĿċūēĿĚƙîĳîĿŠƙƥ} sēūŠūƥƎƑĚǄĚŠƥĿŠĲĚČƥĿūŠɈƎƑĚČŕĿŠĿČîŕîŠēČŕĿŠĿČîŕƙƥƭēĿĚƙƙĺūǅĚēƥĺîƥsɠƙƎĚČĿǶČ ĿŞŞƭŠĿƥǋČîŠƑĚēƭČĚƥĺĚƙĚǄĚƑĿƥǋūĲēĿƙĚîƙĚȂȃȆɈȂȃȉɝȂȄȃ_{ɍŠƥĿċūēĿĚƙēĿƑĚČƥĚēƥūǅîƑēƙs} ĿŠĺĿċĿƥƑĚŕĚîƙĚîŠēƙƎƑĚîēūĲŠĚǅŕǋĲūƑŞĚēǄĿƑƭƙƎîƑƥĿČŕĚƙĲƑūŞĿŠĲĚČƥĚēČĚŕŕƙȂȄȄ_ɍ/îƑŕǋ ČƑǋƙƥîŕŕūĳƑîƎĺĿČ ƙƥƭēĿĚƙ ūĲ s ĺîǄĚ ƙĺūǅŠ ƥĺîƥ îŠƥĿĳĚŠĿČ ƑĚĳĿūŠƙȂȄȅ_{surround the} ĚŠǕǋŞĚɫƙĺĿĳĺŕǋČūŠƙĚƑǄĚēîČƥĿǄĚƙĿƥĚȂȄȆɈȂȄȇ_{îŠēîƑĚĺĿĳĺŕǋǄîƑĿîċŕĚɈŞūƙƥŕĿŒĚŕǋēƭĚƥū}

immune pressureȂȃȄɈȂȃȅ_{ɍ¬ƥƭēĿĚƙČūŞƎîƑĿŠĳƥĺĚîŠƥĿĳĚŠĿČĚǄūŕƭƥĿūŠūĲOîŠēsƭƙĿŠĳ}

a limited number of viruses have discovered that their evolution differs and is often îƙǋŠČĺƑūŠūƭƙȂȃȃɈȂȄȈ_.

'ĚƙƎĿƥĚƥĺĚČūƑƑĚŕîƥĿūŠūĲsǅĿƥĺĿŞŞƭŠĿƥǋîŠēƥĺĚîƙǋŠČĺƑūŠǋĿŠîŠƥĿĳĚŠĿČ ĚǄūŕƭƥĿūŠċĚƥǅĚĚŠOîŠēsɈsĿƙŠūƥƑūƭƥĿŠĚŕǋĚǊîŞĿŠĚēĿŠƙĚƑūĚƎĿēĚŞĿūŕūĳǋūƑ GĿĳƭƑĚȇʯ¹ĺĚsĳŕūċƭŕîƑĺĚîē. Illustration of the tetrameric NA structure of subtype N2 (PDB

code 2BAT115_{) generated with MacPyMOL. The viral receptor sialic acid, shown as red sticks, is}

docked into the active site, represented in yellow, surrounded by the framework sites, depicted in ūƑîŠĳĚɍsŞūŠūŞĚƑƙîƑĚƙĺūǅŠĿŠƙƭƑĲîČĚǶŕŕĚēɠƙƎîČĚɚƥūƎŕĚĲƥɛɈČîƑƥūūŠƑĿċċūŠƙɚƥūƎƑĿĳĺƥîŠē bottom left), and smoothed cartoon loops (bottom right).

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ǄîČČĿŠĚƙƥƭēĿĚƙɍŠƥĿĳĚŠĿČČĺîƑîČƥĚƑĿǕîƥĿūŠūĲsČîŠċĚƎĚƑĲūƑŞĚēƭƙĿŠĳsĿŠĺĿċĿƥĿūŠ ɚsTɛîƙƙîǋƙǅĺĿČĺēĚƥĚƑŞĿŠĚƥĺĚĚǊƥĚŠƥūĲîŠƥĿċūēǋɠŞĚēĿîƥĚēĿŠƥĚƑĲĚƑĚŠČĚǅĿƥĺĚŠǕǋŞĚ îČƥĿǄĿƥǋȂȄȉ_{ɍ ¹ĺĚƙĚ îƙƙîǋƙ ƑĚŕǋ ūŠ ƥĺĚ ĚŠǕǋŞîƥĿČ ƙĿîŕĿēîƙĚ îČƥĿǄĿƥǋ ūĲ sɈ ǅĺĿČĺ Ŀƙ}

ēĚƥĚƑŞĿŠĚēċǋŞĚîƙƭƑĿŠĳČŕĚîǄîĳĚūĲƙĿîŕĿČîČĿēĲƑūŞĺĿĳĺŕǋĳŕǋČūƙǋŕîƥĚēƎƑūƥĚĿŠƙƙƭČĺ îƙĲĚƥƭĿŠɍ¹ĺĚsTƥĺĿūċîƑċĿƥƭƑĿČîČĿēɚ¹ɛîƙƙîǋȂȄȊɈȂȅȁ_{is based on the detection of free}

ƙĿîŕĿČîČĿēɍ¹ĺĿƙîƙƙîǋĿƙƑĚČūŞŞĚŠēĚēċǋƥĺĚØūƑŕēOĚîŕƥĺ~ƑĳîŠĿǕîƥĿūŠɚØO~ɛȂȅȂ_{, but}

ƥĺĚƭƙĚūĲŕîƑĳĚǄūŕƭŞĚƙūĲĺîǕîƑēūƭƙČĺĚŞĿČîŕƙîŠēŕîċūƑĿūƭƙƎƑūČĚēƭƑĚƙĺîƙĿŞƎĚēĚē îŠƥĿĳĚŠĿČČĺîƑîČƥĚƑĿǕîƥĿūŠūĲsēƭƑĿŠĳĿŠǷƭĚŠǕîƙƭƑǄĚĿŕŕîŠČĚɍŕƥĚƑŠîƥĿǄĚîƙƙîǋƙƥĺîƥ ĺîǄĚċĚĚŠēĚǄĚŕūƎĚēĿŠČŕƭēĚîŠĚŠǕǋŞĚɠŕĿŠŒĚēŕĚČƥĿŠîƙƙîǋɚ/ggɛȂȅȃ_{, which also relies on}

ƥĺĚƙĿîŕĿēîƙĚîČƥĿǄĿƥǋūĲsɈċƭƥĿŠƙƥĚîēūĲŞĚîƙƭƑĿŠĳĲƑĚĚƙĿîŕĿČîČĿēɈĿƥēĚƥĚČƥƙƥĺĚƥĚƑŞĿŠîŕ ĳîŕîČƥūƙĚƥĺîƥċĚČūŞĚƙĚǊƎūƙĚēîĲƥĚƑƙĿîŕĿČîČĿēČŕĚîǄîĳĚċǋsɚGĿĳƭƑĚȈċɛɍūƥĺƥĺĚ sT¹îŠēƥĺĚsT/ggŞĚîƙƭƑĚĲƭŠČƥĿūŠîŕĿŠĺĿċĿƥĿūŠūĲsîČƥĿǄĿƥǋċǋîŠƥĿċūēĿĚƙɈîŠē ČūŠƙĚƐƭĚŠƥŕǋĺîǄĚČŕĚîƑƑĚŕĚǄîŠČĚƥūĿŞŞƭŠĿƥǋin vivoȂȄȁɈȂȅȄɈȂȅȅ_. ČūŞƎŕĿČîƥĿūŠūĲsTîƙƙîǋƙĿƙƥĺĚĿŠƥĚƑĲĚƑĚŠČĚūĲOɠƙƎĚČĿǶČîŠƥĿċūēĿĚƙƥĺîƥċŕūČŒ sîČƥĿǄĿƥǋŠūŠɠƙƎĚČĿǶČîŕŕǋǅĺĚŠƥĺĚǋċĿŠēƥūOȂȄȈ_{ɍOȇsǊǄĿƑƭƙĚƙĳĚŠĚƑîƥĚēċǋČŕîƙƙĿČîŕ}

GĿĳƭƑĚȈʯ¤ĚČĚƎƥūƑɠēĚƙƥƑūǋĿŠĳîČƥĿǄĿƥǋūĲŠĚƭƑîŞĿŠĿēîƙĚɍ a | Neuraminidase cleaves sialic acid

ɚsɠîČĚƥǋŕŠĚƭƑîŞĿŠĿČîČĿēɛĲƑūŞƥĺĚČĚŕŕƑĚČĚƎƥūƑɈƑĚƙƭŕƥĿŠĳĿŠƥĺĚƑĚŕĚîƙĚūĲŠĚǅŕǋĲūƑŞĚēĿŠǷƭĚŠǕî virus particles from the cells. ċ | Sialic acid linked to galactose is cleaved, exposing the galactose. Galactose is linked to N-acetylglucosamine (GlcNAc). Adapted from145_.

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ƑĚîƙƙūƑƥŞĚŠƥǅĚƑĚƭƙĚēĿŠƥĺĚƥƑîēĿƥĿūŠîŕ¹ŞĚƥĺūēȂȃȃɈȂȄȉ_{ɍOūǅĚǄĚƑɈƥĺĚĳĚŠĚƑîƥĿūŠūĲ} ƑĚČūŞċĿŠîŠƥǄĿƑƭƙĚƙĿƙƥĿŞĚɠČūŠƙƭŞĿŠĳĲūƑŕîƑĳĚŠƭŞċĚƑƙūĲǄĿƑƭƙĚƙîŠēƥĺĚƑĚĲūƑĚƥĺĿƙ ŞĚƥĺūēĿƙŠūƥƙƭĿƥîċŕĚĲūƑŕîƑĳĚɠƙČîŕĚƙƭƑǄĚĿŕŕîŠČĚūĲîŠƥĿĳĚŠĿČĚǄūŕƭƥĿūŠūĲČĿƑČƭŕîƥĿŠĳ ĿŠǷƭĚŠǕîǄĿƑƭƙĚƙɍGūƑîŠîŕǋƙĿƙūĲƥĺĚîŠƥĿĳĚŠĿČĚǄūŕƭƥĿūŠūĲsĿƥǅūƭŕēċĚĿēĚîŕƥūĺîǄĚ ƥĺĚƎūƙƙĿċĿŕĿƥǋūĲƭƙĿŠĳǅĿŕēƥǋƎĚǄĿƑƭƙĚƙîƙîŠƥĿĳĚŠĿŠîƙƙîǋƙƥĺîƥîƑĚŠūƥĿŞƎîČƥĚēċǋ ŠūŠɠƙƎĚČĿǶČĿŠĺĿċĿƥūƑƙɈĿŠČŕƭēĿŠĳîŠƥĿċūēĿĚƙƥūOɍ ×îČČĿŠĚ ¹ĺĚ ĚĲĲĚČƥ ūĲ îŠƥĿĳĚŠĿČ ēƑĿĲƥ ŞîēĚ Ŀƥ ŠĚČĚƙƙîƑǋ ƥū ƑĚĲūƑŞƭŕîƥĚ ǄîČČĿŠĚƙ îĲƥĚƑ ūŠŕǋ ȃ ǋĚîƑƙ ūĲ ƭƙĚȂȅȇ_{Ɉ îŠē ƥĺĚ ØO~ ĚƙƥîċŕĿƙĺĚē ƥĺĚ ØO~ Hŕūċîŕ TŠǷƭĚŠǕî ¬ƭƑǄĚĿŕŕîŠČĚ} sĚƥǅūƑŒɚHT¬sɛĿŠȂȊȆȃĲūƑƥĺĚĚîƑŕǋēĚƥĚČƥĿūŠūĲēƑĿĲƥĚēƙƥƑîĿŠƙȂȅȈɈȂȅȉ_{renamed to the} Hŕūċîŕ TŠǷƭĚŠǕî ¬ƭƑǄĚĿŕŕîŠČĚ îŠē ¤ĚƙƎūŠƙĚ ¬ǋƙƥĚŞ ɚHT¬¤¬ɛ ĿŠ ȃȁȂȂȂȅȊ_{ɍ ¹ĺĚ ȂȊȇȉ}

pandemic led to the development of the intramuscular trivalent inactivated vaccines ɚ¹T×ƙɛ îĳîĿŠƙƥ T× îŠē T×ȂȆȁ_{ɍ TŠǷƭĚŠǕî ǄîČČĿŠĚƙ ƑĚēƭČĚ ƥĺĚ ŞūƑċĿēĿƥǋ îŠē ŞūƑƥîŕĿƥǋ} îƙƙūČĿîƥĚēǅĿƥĺîŠŠƭîŕĿŠǷƭĚŠǕîĚƎĿēĚŞĿČƙċƭƥŠĚĚēƥūċĚƭƎēîƥĚēĲƑĚƐƭĚŠƥŕǋēƭĚƥū îŠƥĿĳĚŠĿČ ēƑĿĲƥɍ ¹ĺĚ ČƭƑƑĚŠƥ ƙĚîƙūŠîŕ ĿŠǷƭĚŠǕî ǄîČČĿŠĚ Ŀƙ ēĚƙĿĳŠĚē ƥū ƎƑūƥĚČƥ îĳîĿŠƙƥ ČĿƑČƭŕîƥĿŠĳ ɚOȂsȂɛƎēŞȁȊ ǄĿƑƭƙĚƙɈ ɚOȄsȃɛ ǄĿƑƭƙĚƙɈ îŠē T×ɍ ¹ĺūƑūƭĳĺ ƙƭƑǄĚĿŕŕîŠČĚ ċǋƥĺĚsîƥĿūŠîŕTŠǷƭĚŠǕî ĚŠƥƑĚƙîŠēØO~ ūŕŕîċūƑîƥĿŠĳ ĚŠƥƑĚƙǅĿƥĺĿŠƥĺĚØO~ɫƙ HT¬¤¬ Ŀƙ ŠĚĚēĚē ƥū ĿēĚŠƥĿĲǋ ƥĺĚ Şūƙƥ ƙƭĿƥîċŕĚ ƙƥƑîĿŠƙ ƥū ƭƙĚ ĿŠ ǄîČČĿŠĚƙ ĲūƑ ƥĺĚ ŠĚǊƥ epidemicȂȆȂ_{. Representatives of the predominant circulating viruses are sent to the}

ØO~ ūŕŕîċūƑîƥĿŠĳ ĚŠƥƑĚƙɈ ǅĺĿČĺ ƎƑūēƭČĚ ǄîČČĿŠĚ ƙĚĚē ƙƥƑîĿŠƙ ƥĺîƥ ČîŠ ċĚ ƙĺîƑĚē ǅĿƥĺ ǄîČČĿŠĚ ŞîŠƭĲîČƥƭƑĚƑƙɍ ×îČČĿŠĚ ƙƥƑîĿŠ ƙĚŕĚČƥĿūŠ ēĚƎĚŠēƙ ūŠ ƥĺƑĚĚ îƙƎĚČƥƙɇ ĚƎĿēĚŞĿūŕūĳĿČîŕĿŠĲūƑŞîƥĿūŠɈĳĚŠĚƥĿČîŠîŕǋƙĚƙūĲƥĺĚOîŠēsĳĚŠĚƙɈîŠēƙĚƑūŕūĳĿČîŕ îŠîŕǋƙĿƙūĲOɍ¹ĺĚŞîĿŠĲūČƭƙūĲĿŠǷƭĚŠǕîƙƭƑǄĚĿŕŕîŠČĚĿƙūŠOɈîŠēūĲǶČĿîŕĿŠǷƭĚŠǕî ǄîČČĿŠĚƙîƑĚƑĚƐƭĿƑĚēƥūČūŠƥîĿŠȂȆǿĳūĲĚîČĺOƙƭċƥǋƎĚȂȆȃ_{ǅĺĿŕĚƥĺĚîŞūƭŠƥūĲs} ĿƙŠūƥƙƥîŠēîƑēĿǕĚēɍ×îČČĿŠĚĚĲĲĚČƥĿǄĚŠĚƙƙɚ×/ɛĿƙēĚƎĚŠēĚŠƥūŠĺūǅǅĚŕŕƥĺĚǄîČČĿŠĚ ƙƥƑîĿŠƙŞîƥČĺƥĺĚČĿƑČƭŕîƥĿŠĳĿŠǷƭĚŠǕîƙƥƑîĿŠƙɈîŠēĚƙƥĿŞîƥĚƙƙĺūǅĚēî×/ūĲȂȁʣĿŠ ȃȁȁȅɝȃȁȁȆɈȃȂʣĿŠȃȁȁȆɝȃȁȁȇɈîŠēȆȃʣĿŠȃȁȁȇɝȃȁȁȈȂȆȄ_. ¬ČūƎĚūĲƥĺĿƙƥĺĚƙĿƙ ¹ĺĚƑĚĿƙƙƥĿŕŕŞƭČĺƭŠČĚƑƥîĿŠƥǋîċūƭƥƥĺĚƭŠēĚƑŕǋĿŠĳŞĚČĺîŠĿƙŞƙƥĺîƥĳūǄĚƑŠîŠƥĿĳĚŠĿČ ēƑĿĲƥ ūĲ ĿŠǷƭĚŠǕî ǄĿƑƭƙĚƙɈ îŠē ƙĚǄĚƑîŕ ƥĺĚūƑĿĚƙ ĺîǄĚ ċĚĚŠ ƎƑūƎūƙĚēɍ ¹ĺĚƙĚ ƥĺĚūƑĿĚƙ ČūŠƙĿēĚƑOƥūċĚƥĺĚƎƑĿŞîƑǋēƑĿǄĿŠĳĲūƑČĚɈǅĺĿŕĚƥĺĚƙĚČūŠēŒĚǋƙƭƑĲîČĚĳŕǋČūƎƑūƥĚĿŠ ɚsɛîŠēƥĺĚūƥĺĚƑǄĿƑîŕƎƑūƥĚĿŠƙĺîǄĚŕîƑĳĚŕǋċĚĚŠĿĳŠūƑĚēɍ¹ĺĿƙƥĺĚƙĿƙĲūČƭƙĚƙūŠîŕŕ

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ĿŠǷƭĚŠǕîƎƑūƥĚĿŠƙɈǅĿƥĺƙƎĚČĿîŕĚŞƎĺîƙĿƙūŠsɈƥūċĚƥƥĚƑƭŠēĚƑƙƥîŠēɜîŠēƭŕƥĿŞîƥĚŕǋ ƎƑĚēĿČƥɜƥĺĚČūŞƎŕĚǊĚǄūŕƭƥĿūŠūĲɚOȄsȃɛǄĿƑƭƙĚƙɍ TŠČĺîƎƥĚƑȃƥĺĚĳĚŠĚƥĿČĚǄūŕƭƥĿūŠūĲsĿƙČūŞƎîƑĚēǅĿƥĺOȂƭƙĿŠĳîŠĚǊƥĚŠƙĿǄĚ ēîƥîƙĚƥČūŠƥîĿŠĿŠĳǄĿƑƭƙĿƙūŕîƥĚƙūċƥîĿŠĚēĲƑūŞČūŠƙĚČƭƥĿǄĚĿŠǷƭĚŠǕîƙĚîƙūŠƙĲƑūŞȂȊȇȉ ƥĿŕŕƥĺĚȃȁȁȊɠȃȁȂȁƙĚîƙūŠɍ¹ĺĚîŠƥĿĳĚŠĿČƎƑūƎĚƑƥĿĚƙîƙŞĚîƙƭƑĚēċǋƥĺĚOTîƙƙîǋǅĚƑĚ ŒŠūǅŠɈîŠēǅĿƥĺƥĺĿƙĿŠĲūƑŞîƥĿūŠɈƑĚîƙƙūƑƥŞĚŠƥĚǄĚŠƥƙɈƑîƥĚƙūĲĚǄūŕƭƥĿūŠîƑǋČĺîŠĳĚɈîŠē ƙĚŕĚČƥĿūŠƎƑĚƙƙƭƑĚƙǅĚƑĚîŠîŕǋƙĚēūǄĚƑȅȁǋĚîƑƙūĲĿŠǷƭĚŠǕîɚOȄsȃɛǄĿƑƭƙĚǄūŕƭƥĿūŠɍTŠ ČĺîƎƥĚƑȄɈîƙĿŞĿŕîƑîƎƎƑūîČĺĿƙƭƙĚēƥūƙƥƭēǋƥĺĚĲƭŕŕĿŠǷƭĚŠǕîǄĿƑƭƙĳĚŠūŞĚƙîŠēƥĺĚĿƑ relation to antigenic change.

ĺîƎƥĚƑȅƭƥĿŕĿǕĚƙƥĺĚ¹sTîƙƙîǋƥūČĺîƑîČƥĚƑĿǕĚîŠƥĿĳĚŠĿČĚǄūŕƭƥĿūŠūĲs ĿŠĺƭŞîŠɚOȂsȂɛîŠēɚOȄsȃɛǄĿƑƭƙĚƙƑĚČūŞŞĚŠēĚēĲūƑÀŠĿƥĚē¬ƥîƥĚƙūĲŞĚƑĿČî ĿŠǷƭĚŠǕîǄîČČĿŠĚƙċĚƥǅĚĚŠȂȊȊȆîŠēȃȁȂȁɍ¹ĺĚ¹sTîƙƙîǋƙîƑĚƎĚƑĲūƑŞĚēƭƙĿŠĳ ĲĚƑƑĚƥîŠƥĿƙĚƑîēĿƑĚČƥĚēîĳîĿŠƙƥǅĿŕēɠƥǋƎĚɚOȂsȂɛîŠēɚOȄsȃɛǄĿƑƭƙĚƙɈîŠēîƙîŠƥĿĳĚŠƙ ǄĿƑƭƙƑĚîƙƙūƑƥîŠƥƙǅĿƥĺƥĺĚƥîƑĳĚƥĚēsîŠēîŞĿƙŞîƥČĺĚēOūĲƥĺĚOȇƙƭċƥǋƎĚɍÀƙĚūĲ ƥĺĚƙĚƑĚîƙƙūƑƥîŠƥƙƎƑĚǄĚŠƥƙĲîŕƙĚsTƙĿĳŠîŕƙēƭĚƥūĿŠƥĚƑĲĚƑĿŠĳOîŠƥĿċūēĿĚƙɍŠƥĿĳĚŠĿČ maps were constructed from the data sets using multidimensional scaling, to position ƥĺĚîŠƥĿĳĚŠƙîŠēîŠƥĿƙĚƑîūŠƥĺĚŞîƎɈîƙƎƑĚǄĿūƭƙŕǋēĚƙČƑĿċĚēȂȁȈ_.

ĚČîƭƙĚƥĺĚČūŠǄĚŠƥĿūŠîŕsTîƙƙîǋƙîƑĚČƭŞċĚƑƙūŞĚîŠēŕîċūƑĿūƭƙɈČƑĿƥĿČîŕƙƥĚƎƙ ĿŠƥĺĚsT/ggǅĚƑĚŞūēĿǶĚēîŠēūƎƥĿŞĿǕĚēƥūƙƭƎƎūƑƥƥĺĚƭƙĚūĲƥĺĚsT/ggĿŠĺƭŞîŠ ƙĚƑūŕūĳǋĿŠČĺîƎƥĚƑȆ. ĺîƎƥĚƑȇ describes the steps that are important for obtaining ČūŠƙĿƙƥĚŠƥƑĚƙƭŕƥƙǅĿƥĺƥĺĚsT/ggĿŠîĲūƑŞîƥƙƭĿƥîċŕĚĲūƑƑîƎĿēîŠƥĿĳĚŠĿČČĺîƑîČƥĚƑĿǕîƥĿūŠ ūĲsɈǅĿƥĺǅĿŕēƥǋƎĚǄĿƑƭƙĚƙîƙîŠƥĿĳĚŠɍTŠƥĚƑĲĚƑĚŠČĚċǋîŠƥĿċūēĿĚƙēĿƑĚČƥĚēîĳîĿŠƙƥO ūĲǅĿŕēƥǋƎĚɚOȄsȃɛǄĿƑƭƙĚƙĿƙƎƑĚǄĚŠƥĚēċǋƑîĿƙĿŠĳĲĚƑƑĚƥƙĚƑîîĳîĿŠƙƥƑĚČūŞċĿŠîŠƥ ĿŠǷƭĚŠǕîOȈsȃɚɚOȈsȃɛɛǄĿƑƭƙĚƙƥĺîƥČūŠƥîĿŠƥĺĚsūĲǄîƑĿūƭƙɚOȄsȃɛǄĿƑƭƙĚƙɍ ¹ĺƑūƭĳĺƥĺĿƙîƎƎƑūîČĺĿƥĿƙƎūƙƙĿċŕĚƥūƙČƑĚĚŠǅĿŕēƥǋƎĚǄĿƑƭƙĚƙɈƥĺƭƙƎƑĚǄĚŠƥĿŠĳƥĺĚ ƥĿŞĚɠČūŠƙƭŞĿŠĳĳĚŠĚƑîƥĿūŠūĲƑĚČūŞċĿŠîŠƥǄĿƑƭƙĚƙūƑƎƑūƥĚĿŠƙĲūƑĚîČĺĚƎĿēĚŞĿČǄĿƑƭƙ ūĲĿŠƥĚƑĚƙƥɍGĿŠîŕŕǋɈĿŠČĺîƎƥĚƑȈɈƥĺĚūƎƥĿŞĿǕĚēsT/ggĿƙƭƙĚēƥūîŠîŕǋƙĚƑūƭĳĺŕǋƥĺƑĚĚ ĺƭŠēƑĚēǄĿƑƭƙĚƙĲƑūŞȂȊȇȉƥĿŕŕƥĺĚȃȁȂȁɠȃȁȂȂƙĚîƙūŠɍ¹ĺĚƑĚƙƭŕƥĿŠĳîŠƥĿĳĚŠĿČŞîƎūĲ sĿƙČūŞƎîƑĚēƥūƥĺĚîŠƥĿĳĚŠĿČŞîƎūĲOɍ ¹ĺĚƑĚƙƭŕƥƙūĲîŕŕƙƥƭēĿĚƙɈîŠēƥĺĚĿŞƎŕĿČîƥĿūŠƙƥĺĚǋĺîǄĚūŠĲƭƥƭƑĚƑĚƙĚîƑČĺɈîƑĚ discussed in ČĺîƎƥĚƑȉ.

1

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Journal of General Virology, volume 93(9), 1 September 2012, pages 1996-2007

Kim B. Westgeest, Miranda de Graaf, Mathieu Fourment, Theo M. Bestebroer,

¤ƭƭēǄîŠĚĚŒɈqūŠĿƐƭĚTɍcɍ¬ƎƑūŠŒĚŠɈcîŠ ɍēĚcūŠĳɈHƭƭƙGɍ¤ĿŞŞĚŕǕǅîîŠɈ ūŕĿŠ¤ƭƙƙĚŕŕɈŕċĚƑƥ'ɍqɍ/ɍ~ƙƥĚƑĺîƭƙɈHîǄĿŠcɍ'ɍ¬ŞĿƥĺɈ'ĚƑĚŒcɍ¬ŞĿƥĺɈ ¤ūŠɍqɍGūƭČĺĿĚƑ

Genetic Evolution of Neuraminidase

RI,QÁXHQ]D$+19LUXVHVIURP

1968 to 2009 and its Correspondence

to Haemagglutinin

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¬¹¤ ¹

/îČĺ ǋĚîƑɈ ĿŠǷƭĚŠǕî ǄĿƑƭƙĚƙ ČîƭƙĚ ĚƎĿēĚŞĿČƙ ċǋ ĚǄîēĿŠĳ ƎƑĚɠĚǊĿƙƥĿŠĳ ĺƭŞūƑîŕ ĿŞŞƭŠĿƥǋƥĺƑūƭĳĺŞƭƥîƥĿūŠƙĿŠƥĺĚŞîŏūƑĳŕǋČūƎƑūƥĚĿŠƙɇƥĺĚĺîĚŞîĳĳŕƭƥĿŠĿŠɚOɛîŠē ƥĺĚ ŠĚƭƑîŞĿŠĿēîƙĚ ɚsɛɍ TŠ ȃȁȁȅɈ ƥĺĚ îŠƥĿĳĚŠĿČ ĚǄūŕƭƥĿūŠ ūĲ O ūĲ ĺƭŞîŠ ĿŠǷƭĚŠǕî ɚOȄsȃɛǄĿƑƭƙĚƙǅîƙŞîƎƎĚēĲƑūŞĿƥƙĿŠƥƑūēƭČƥĿūŠĿŠĺƭŞîŠƙĿŠȂȊȇȉƭŠƥĿŕȃȁȁȄȂȁȈ_. ¹ĺĚ ČƭƑƑĚŠƥ ƙƥƭēǋ ĲūČƭƙĚē ūŠ ƥĺĚ ĳĚŠĚƥĿČ ĚǄūŕƭƥĿūŠ ūĲ s îŠē ČūŞƎîƑĚē Ŀƥ ǅĿƥĺ O ƭƙĿŠĳƥĺĚēîƥîƙĚƥūĲ¬ŞĿƥĺîŠēČūŕŕĚîĳƭĚƙɈƭƎēîƥĚēƥūƥĺĚĚƎĿēĚŞĿČūĲƥĺĚȃȁȁȊɓȃȁȂȁ ƙĚîƙūŠɍ¡ĺǋŕūĳĚŠĚƥĿČƥƑĚĚƙîŠēĳĚŠĚƥĿČŞîƎƙǅĚƑĚČūŠƙƥƑƭČƥĚēƥūǄĿƙƭîŕĿǕĚƥĺĚĳĚŠĚƥĿČ ĚǄūŕƭƥĿūŠ ūĲ s îŠē Oɍ ¹ĺĚ ƑĚƙƭŕƥƙ ƑĚǄĚîŕĚē ŞƭŕƥĿƎŕĚ ƑĚîƙƙūƑƥŞĚŠƥ ĚǄĚŠƥƙ ūǄĚƑ ƥĺĚ ǋĚîƑƙɍ ~ǄĚƑîŕŕ ƑîƥĚƙ ūĲ ĚǄūŕƭƥĿūŠîƑǋ ČĺîŠĳĚ ǅĚƑĚ ŕūǅĚƑ ĲūƑ s ƥĺîŠ ĲūƑ OȂ îƥ ƥĺĚ nucleotide level. Selection pressures were estimated, revealing an abundance of ŠĚĳîƥĿǄĚŕǋ ƙĚŕĚČƥĚē ƙĿƥĚƙ îŠē ƙƎîƑƙĚ ƎūƙĿƥĿǄĚŕǋ ƙĚŕĚČƥĚē ƙĿƥĚƙɍ ¹ĺĚ ēĿĲĲĚƑĚŠČĚƙ ĲūƭŠē ċĚƥǅĚĚŠƥĺĚĚǄūŕƭƥĿūŠūĲsîŠēOȂǅîƑƑîŠƥĲƭƑƥĺĚƑîŠîŕǋƙĿƙūĲƥĺĚĚǄūŕƭƥĿūŠūĲs îƥƥĺĚƎĺĚŠūƥǋƎĿČŕĚǄĚŕɈîƙĺîƙċĚĚŠēūŠĚƎƑĚǄĿūƭƙŕǋĲūƑOɍ

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Ts¹¤~'À ¹T~s

TŠǷƭĚŠǕî ĚƎĿēĚŞĿČƙ îĲĲĚČƥ îƎƎƑūǊĿŞîƥĚŕǋ ȆɝȂȆ ʣ ūĲ ƥĺĚ ǅūƑŕē ƎūƎƭŕîƥĿūŠ ƑĚƙƭŕƥĿŠĳ ĿŠ îŠ ĚƙƥĿŞîƥĚē ȄɝȆ ŞĿŕŕĿūŠ ĺūƙƎĿƥîŕĿǕîƥĿūŠƙ îŠē ċĚƥǅĚĚŠ ȃȆȁɈȁȁȁ îŠē ȆȁȁɈȁȁȁ ēĚîƥĺƙ îŠŠƭîŕŕǋȅȁɈȂȆȅ_{ɍ TŠǷƭĚŠǕî ƥǋƎĚ ǄĿƑƭƙĚƙ ČîŠ ċĚ ēĿǄĿēĚē ĿŠƥū ƙƭċƥǋƎĚƙ ċîƙĚē ūŠ} ƥĺĚ îŠƥĿĳĚŠĿČ ƎƑūƎĚƑƥĿĚƙ ūĲ ƥĺĚ ŞîŏūƑ ƙƭƑĲîČĚ ĳŕǋČūƎƑūƥĚĿŠƙ ĺîĚŞîĳĳŕƭƥĿŠĿŠ ɚOɛ îŠē ŠĚƭƑîŞĿŠĿēîƙĚ ɚsɛɍ ¹ū ēîƥĚɈ ȂȈ OȂȅɈȂȆ_{îŠē ŠĿŠĚ s}ȂȈ_{ƙƭċƥǋƎĚƙ ĺîǄĚ ċĚĚŠ ĲūƭŠē} ĿŠ ŠîƥƭƑĚɍ ¬ƭċƥǋƎĚƙ ɚOȂsȂɛ îŠē ɚOȄsȃɛ îƑĚ ČƭƑƑĚŠƥŕǋ ƥĺĚ ČîƭƙîƥĿǄĚ îĳĚŠƥƙ ūĲ ĿŠǷƭĚŠǕîǄĿƑƭƙĚƎĿēĚŞĿČƙĿŠĺƭŞîŠƙɈūĲǅĺĿČĺƥĺĚĿŠǷƭĚŠǕîɚOȄsȃɛǄĿƑƭƙĚƙîƑĚƥĺĚ most recurring and virulentȂȆȆɈȂȆȇ_{and show the strongest antigenic drift}ȊȆ_.

OɈîĺūŞūƥƑĿŞĚƑĿČƥǋƎĚTĿŠƥĚĳƑîŕŞĚŞċƑîŠĚƎƑūƥĚĿŠɈŞĚēĿîƥĚƙǄĿƑîŕĚŠƥƑǋĿŠƥūƥĺĚ ČĚŕŕċǋċĿŠēĿŠĳƥūƙĿîŕĿČîČĿēƙȆȉ_{ɍsɈîƥĚƥƑîŞĚƑĿČƥǋƎĚTTĿŠƥĚĳƑîŕŞĚŞċƑîŠĚƎƑūƥĚĿŠǅĿƥĺ} ƙĿîŕĿēîƙĚîČƥĿǄĿƥǋɈîŕŕūǅƙǄĿƑƭƙƑĚŕĚîƙĚĲƑūŞƥĺĚČĚŕŕȇȇɝȇȉ_{ɍūƥĺOîŠēsîƑĚŕūČîƥĚēūŠ} ƥĺĚƙƭƑĲîČĚūĲƥĺĚǄĿƑîŕŞĚŞċƑîŠĚîŠēîƑĚƥĺĚŞîĿŠƥîƑĳĚƥƙĲūƑîŠƥĿċūēĿĚƙɍŠƥĿċūēĿĚƙ îĳîĿŠƙƥĿŠǷƭĚŠǕîǄĿƑƭƙĚƙƑĚƙƭŕƥĿŠƎƑūƥĚČƥĿǄĚĿŞŞƭŠĿƥǋɈċƭƥŞƭƥîƥĿūŠƙĿŠOîŠēsîŕŕūǅ ƥĺĚǄĿƑƭƙƥūĚƙČîƎĚĺūƙƥĿŞŞƭŠĿƥǋɍ¹ĺĿƙƎƑūČĚƙƙɈŒŠūǅŠîƙîŠƥĿĳĚŠĿČēƑĿĲƥȂȆȈ_{, is responsible} ĲūƑƥĺĚƑĚČƭƑƑĚŠČĚūĲĿŠǷƭĚŠǕîĚƎĿēĚŞĿČƙîŕŞūƙƥĚǄĚƑǋǅĿŠƥĚƑɍ ×îČČĿŠĚƙĺîǄĚƎƑūǄĚŠĚĲĲĚČƥĿǄĚɈċƭƥŠĚĚēƥūċĚƭƎēîƥĚēĲƑĚƐƭĚŠƥŕǋēƭĚƥūîŠƥĿĳĚŠĿČ ēƑĿĲƥɍ¬ĿŠČĚȂȊȊȊɈƥĺĚĿŠǷƭĚŠǕîɚOȄsȃɛǄĿƑƭƙČūŞƎūŠĚŠƥĺîƙċĚĚŠƭƎēîƥĚēƙĿǊƥĿŞĚƙȂȆȆ_. ¹ĺūƑūƭĳĺƙƭƑǄĚĿŕŕîŠČĚċǋƥĺĚsîƥĿūŠîŕTŠǷƭĚŠǕî ĚŠƥƑĚƙîŠēØO~ ūŕŕîċūƑîƥĿŠĳ ĚŠƥƑĚƙ ǅĿƥĺĿŠƥĺĚØūƑŕēOĚîŕƥĺ~ƑĳîŠĿǕîƥĿūŠɫƙHŕūċîŕTŠǷƭĚŠǕî¬ƭƑǄĚĿŕŕîŠČĚsĚƥǅūƑŒĿƙƑĚƐƭĿƑĚē ƥūĿēĚŠƥĿĲǋƥĺĚŞūƙƥƙƭĿƥîċŕĚƙƥƑîĿŠƙƥūƭƙĚĿŠǄîČČĿŠĚƙĲūƑƥĺĚŠĚǊƥĚƎĿēĚŞĿČȂȆȂɈȂȆȆ_{. Vaccine} ƙƥƑîĿŠƙĚŕĚČƥĿūŠēĚƎĚŠēƙūŠƥĺƑĚĚîƙƎĚČƥƙɇĚƎĿēĚŞĿūŕūĳĿČîŕĿŠĲūƑŞîƥĿūŠɈOîŠēsĳĚŠĚ ƙĚƐƭĚŠČĚƎĺǋŕūĳĚŠǋîŠēƙĚƑūŕūĳĿČîŕîŠîŕǋƙĿƙƭƙĿŠĳîŠOĿŠĺĿċĿƥĿūŠîƙƙîǋɍ¹ĺĚŞîĿŠĲūČƭƙ ūĲĳĚŠĚƥĿČîŠēîŠƥĿĳĚŠĿČƙƭƑǄĚĿŕŕîŠČĚĿƙūŠOɈîŠēūĲǶČĿîŕĿŠǷƭĚŠǕîǄîČČĿŠĚĲūƑŞƭŕîƥĿūŠƙ ƎƑĚƙČƑĿċĚƥĺĚîŞūƭŠƥūĲOȂȆȉ_. ŕƥĺūƭĳĺîŠƥĿċūēĿĚƙîĳîĿŠƙƥsēūŠūƥƎƑĚǄĚŠƥĿŠĲĚČƥĿūŠɈŠƭŞĚƑūƭƙƎƑĚČŕĿŠĿČîŕîŠē ČŕĿŠĿČîŕƙƥƭēĿĚƙĿŠēĿČîƥĚîƑūŕĚūĲsĿŞŞƭŠĿƥǋĿŠƑĚēƭČĿŠĳƥĺĚƙĚǄĚƑĿƥǋūĲĿŠǷƭĚŠǕîǄĿƑƭƙ infectionȂȃȆɈȂȃȉɝȂȄȃ_{ɍ/îƑŕǋČƑǋƙƥîŕŕūĳƑîƎĺĿČƙƥƭēĿĚƙūĲsĺîǄĚƙĺūǅŠƥĺîƥîŠƥĿĳĚŠĿČƑĚĳĿūŠƙ} ƙƭƑƑūƭŠēƥĺĚĚŠǕǋŞĚɫƙĺĿĳĺŕǋČūŠƙĚƑǄĚēîČƥĿǄĚƙĿƥĚȂȄȆɈȂȄȇ_{ɍŠƥĿĳĚŠĿČƙĿƥĚƙɈîŠē}ȂȄȅ ǅĚƑĚƙĺūǅŠƥūċĚĺĿĳĺŕǋǄîƑĿîċŕĚƎƑūċîċŕǋēƭĚƥūîŠƥĿĳĚŠĿČēƑĿĲƥȂȃȄɈȂȃȅ_{. Studies comparing} ƥĺĚîŠƥĿĳĚŠĿČēƑĿĲƥūĲOîŠēsƭƙĿŠĳŕĿŞĿƥĚēŠƭŞċĚƑƙūĲǄĿƑƭƙĚƙĺîǄĚƑĚǄĚîŕĚēƥĺîƥƥĺĚĿƑ ĚǄūŕƭƥĿūŠēĿĲĲĚƑƙîŠēĿƙūĲƥĚŠîƙǋŠČĺƑūŠūƭƙȂȃȃɈȂȄȈɈȂȆȊ_{. Given these factors, understanding}

ƥĺĚƎîƥƥĚƑŠƙūĲĚǄūŕƭƥĿūŠĿŠsĿƙĿŞƎūƑƥîŠƥɍ

TŠȃȁȁȅɈ¬ŞĿƥĺĚƥîŕɍŞîƎƎĚēƥĺĚîŠƥĿĳĚŠĿČĚǄūŕƭƥĿūŠūĲOūĲĺƭŞîŠĿŠǷƭĚŠǕî ɚOȄsȃɛǄĿƑƭƙĲƑūŞĿƥƙĿŠƥƑūēƭČƥĿūŠĿŠĺƭŞîŠƙĿŠȂȊȇȉƭŠƥĿŕȃȁȁȄȂȁȈ_{ɍ¹ĺĚƙƥƭēǋǅîƙ}

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ċîƙĚēūŠîŠĚǊƥĚŠƙĿǄĚēîƥîƙĚƥɈČūŞƎƑĿƙĿŠĳĿŠǷƭĚŠǕîǄĿƑƭƙĿƙūŕîƥĚƙūċƥîĿŠĚēǅĿƥĺĿŠĚîČĺ ĿŠǷƭĚŠǕîƙĚîƙūŠɍOĚƑĚɈǅĚĲūČƭƙĚēūŠƥĺĚĳĚŠĚƥĿČĚǄūŕƭƥĿūŠūĲsîŠēČūŞƎîƑĚēĿƥǅĿƥĺ OȂɚƥĺĚĿŞŞƭŠūĳĚŠĿČƙĚČƥĿūŠūĲƥĺĚOɛɈƭƙĿŠĳƥĺĚēîƥîƙĚƥūĲ¬ŞĿƥĺĚƥîŕ., updated ƥūƥĺĚĚƎĿēĚŞĿČūĲƥĺĚȃȁȁȊɓȃȁȂȁƙĚîƙūŠɍ¤ĚîƙƙūƑƥŞĚŠƥĚǄĚŠƥƙɈƑîƥĚƙūĲĚǄūŕƭƥĿūŠîƑǋ ČĺîŠĳĚɈîŠēƙĚŕĚČƥĿūŠƎƑĚƙƙƭƑĚƙǅĚƑĚîŠîŕǋƙĚēūǄĚƑȅȁǋĚîƑƙūĲĿŠǷƭĚŠǕîɚOȄsȃɛǄĿƑƭƙ ĚǄūŕƭƥĿūŠɍ¹ĺĚēĿĲĲĚƑĚŠČĚƙĲūƭŠēċĚƥǅĚĚŠƥĺĚĚǄūŕƭƥĿūŠūĲsîŠēOȂǅîƑƑîŠƥĲƭƑƥĺĚƑ îŠîŕǋƙĿƙūĲƥĺĚîŠƥĿĳĚŠĿČƎƑūƎĚƑƥĿĚƙūĲsɍ

q¹/¤Tg¬s'q/¹O~'¬

×ĿƑƭƙĚƙ OƭŞîŠĿŠǷƭĚŠǕîɚOȄsȃɛǄĿƑƭƙĚƙɈĿƙūŕîƥĚēūǄĚƑȄȆǋĚîƑƙūĲĿŠǷƭĚŠǕîǄĿƑƭƙƙƭƑǄĚĿŕŕîŠČĚ ċĚƥǅĚĚŠȂȊȇȉîŠēȃȁȁȄƥĺîƥǅĚƑĚƭƙĚēĿŠƥĺĚƙƥƭēǋūĲ¬ŞĿƥĺĚƥîŕɍĿŠȃȁȁȅȂȁȈ_served îƙ ƥĺĚ ċîƙĿƙ ĲūƑ ƥĺĿƙ ƙƥƭēǋɍ ¹ǅū ǄĿƑƭƙĚƙ ǅĿƥĺĿŠ ƥĺĿƙ ēîƥî ƙĚƥ ǅĚƑĚ Šū ŕūŠĳĚƑ îǄîĿŕîċŕĚ ɚɓ×ĿČƥūƑĿîɓȈɓȉȈîŠēɓsĚƥĺĚƑŕîŠēƙɓȅȅȁɓȊȄɛîŠēǅĚƑĚƥĺƭƙĚǊČŕƭēĚēĲƑūŞƥĺĚēîƥîƙĚƥɍ ¹ĺĚēîƥîƙĚƥǅîƙƭƎēîƥĚēǅĿƥĺȂȊĿŠǷƭĚŠǕîɚOȄsȃɛǄĿƑƭƙĚƙČĿƑČƭŕîƥĿŠĳċĚƥǅĚĚŠȃȁȁȄ îŠēȃȁȁȊɈĿŠČŕƭēĿŠĳƙĚǄĚŠǄîČČĿŠĚūƑƑĚĲĚƑĚŠČĚƙƥƑîĿŠƙîŠēȂȃĿƙūŕîƥĚƙĲƑūŞĚƎĿēĚŞĿČƙ ĿŠƥĺĚsĚƥĺĚƑŕîŠēƙɍ¹ĺĚŕîƥƥĚƑȂȃĿƙūŕîƥĚƙǅĚƑĚČĺūƙĚŠċîƙĚēūŠēĿǄĚƑĳĚŠƥƎŕîČĚŞĚŠƥ ĿŠƥĺĚƭƎēîƥĚēɚOȄsȃɛîŠƥĿĳĚŠĿČŞîƎȂȇȁ_{ɍ¹ĺĿƙŕĚēƥūîƥūƥîŕūĲȃȊȂĺƭŞîŠĿŠǷƭĚŠǕî} ɚOȄsȃɛǄĿƑƭƙĚƙɍOƭŞîŠĿŠǷƭĚŠǕîɚOȄsȃɛǄĿƑƭƙĚƙǅĚƑĚƎƑūƎîĳîƥĚēĿŠqîēĿŠɝ'îƑċǋ ČîŠĿŠĚ ŒĿēŠĚǋ ɚq' eɛ ČĚŕŕƙ ūƑɈ ĿĲ ƭŠƙƭČČĚƙƙĲƭŕɈ ĿŠ ȂȂɠēîǋɠūŕē ĚŞċƑǋūŠîƥĚē ČĺĿČŒĚŠ eggs. ¬ĚƐƭĚŠČĚîŠîŕǋƙĿƙ q' e ƙƭƎĚƑŠîƥîŠƥ ūƑ îŕŕîŠƥūĿČ ǷƭĿē ǅîƙ ƭƙĚē ĲūƑ ¤s ĚǊƥƑîČƥĿūŠɈ ƭƙĿŠĳ î OĿĳĺ ¡ƭƑĚ ¤s TƙūŕîƥĿūŠ eĿƥ ɚ¤ūČĺĚ ƎƎŕĿĚē ¬ČĿĚŠČĚɛ îŠē Č's ǅîƙ ƙǋŠƥĺĚƙĿǕĚē ǅĿƥĺ SuperScript®_{TTT ƑĚǄĚƑƙĚ ƥƑîŠƙČƑĿƎƥîƙĚ ɚTŠǄĿƥƑūĳĚŠɛɍ ¹ĺĚ ČūŞƎŕĚƥĚ s îŠē OȂ ĳĚŠĚ} ƙĚĳŞĚŠƥƙ ǅĚƑĚ îŞƎŕĿǶĚē ċǋ ¡ ¤ ƭƙĿŠĳ ŞƎŕĿ¹îƐ Hūŕē®_{'s ƎūŕǋŞĚƑîƙĚ ɚƎƎŕĿĚē} ĿūƙǋƙƥĚŞƙɛ îŠē ƎƭƑĿǶĚē ċǋ ĳĚŕ ĚǊƥƑîČƥĿūŠ ǅĿƥĺ ƥĺĚ £TƐƭĿČŒ HĚŕ /ǊƥƑîČƥĿūŠ eĿƥ ɚ£ĿîĳĚŠɛɍ¬ĚƐƭĚŠČĿŠĳǅîƙƎĚƑĲūƑŞĚēǅĿƥĺsūƑOƙƎĚČĿǶČƎƑĿŞĚƑƙƭƙĿŠĳîĿĳ'ǋĚ ¹ĚƑŞĿŠîƥūƑǄĚƑƙĿūŠȄɍȂČǋČŕĚƙĚƐƭĚŠČĿŠĳŒĿƥɚƎƎŕĿĚēĿūƙǋƙƥĚŞƙɛîŠēîȄȂȁȁHĚŠĚƥĿČ ŠîŕǋǕĚƑɚƎƎŕĿĚēĿūƙǋƙƥĚŞƙɛɈîČČūƑēĿŠĳƥūƥĺĚĿŠƙƥƑƭČƥĿūŠƙūĲƥĺĚŞîŠƭĲîČƥƭƑĚƑɍ sƭČŕĚūƥĿēĚƙĚƐƭĚŠČĚƙūĲƥĺĚsūƎĚŠƑĚîēĿŠĳĲƑîŞĚƙɚ~¤GɛîŠēOȂČūēĿŠĳ regions were aligned using the ClustalW program running within the BioEdit software ƎîČŒîĳĚɈǄĚƑƙĿūŠȈɍȁɍȊɍȁȂȉȅ_{ɍ¬ĚǄĚŠOȂîŠēȂȅsƙĚƐƭĚŠČĚƙČūŠƥîĿŠĚēūŠĚūƑŞūƑĚ}

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ēĚĳĚŠĚƑîƥĚ ŠƭČŕĚūƥĿēĚ ŕĚē ƥū ēĚĳĚŠĚƑîƥĚ îŞĿŠū îČĿē ƎūƙĿƥĿūŠƙɍ ~ŠĚ s ƙĚƐƭĚŠČĚ ČūŠƥîĿŠĚēîŠĿŠƙĚƑƥĿūŠūĲȄŠƭČŕĚūƥĿēĚƙċĚƥǅĚĚŠČūēūŠƙȃȃȂîŠēȃȃȃɈîŠēūŠĚƙĚƐƭĚŠČĚ ĺîēîȄɠŠƭČŕĚūƥĿēĚēĚŕĚƥĿūŠîƥČūēūŠȂȆȅɍsĚǅŕǋƙĚƐƭĚŠČĚēîŠēƎƑĚǄĿūƭƙŕǋƎƭċŕĿƙĺĚēs îŠēOȂēūŞîĿŠîČČĚƙƙĿūŠŠƭŞċĚƑƙîƑĚƎƑūǄĿēĚēĿŠƥĺĚ¬ƭƎƎŕĚŞĚŠƥîƑǋēîƥîɍ ¡ĺǋŕūĳĚŠǋ sƭČŕĚūƥĿēĚ ƙĚƐƭĚŠČĚ îŕĿĳŠŞĚŠƥƙ ǅĿƥĺ ūƑ ǅĿƥĺūƭƥ îŠ îēēĿƥĿūŠîŕ ūƭƥĳƑūƭƎ ɚɓ'ƭČŒɓOūŒŒîĿēūɓȄȄɓȉȁĲūƑOȂîŠēɓcîƎîŠɓȄȁȆɓȂȊȆȈĲūƑsɛǅĚƑĚĳĚŠĚƑîƥĚēɍØĿƥĺ ƥĺĚƙĚ ŠƭČŕĚūƥĿēĚ ƙĚƐƭĚŠČĚ îŕĿĳŠŞĚŠƥƙɈ ƥĺĚ ċĚƙƥɠǶƥ ŞūēĚŕƙ ūĲ ŠƭČŕĚūƥĿēĚ ƙƭċƙƥĿƥƭƥĿūŠ ǅĚƑĚēĚƥĚƑŞĿŠĚēċǋŏqūēĚŕ¹ĚƙƥȂȉȆ_{ɍTŠîŕŕČîƙĚƙɈƥĺĚƎƑĚĲĚƑƑĚēŞîǊĿŞƭŞŕĿŒĚŕĿĺūūēɚqgɛ} ūƎƥĿŞĿǕĚēŞūēĚŕūĲŠƭČŕĚūƥĿēĚƙƭċƙƥĿƥƭƥĿūŠǅîƙ¹×qʋTʋȳȅɚƥƑîŠƙǄĚƑƙĿūŠŞūēĚŕǅĿƥĺƥĺĚ ƎƑūƎūƑƥĿūŠ ūĲ ĿŠǄîƑĿîŠƥ ƙĿƥĚƙ îŠē ƥĺĚ ĳîŞŞî ēĿƙƥƑĿċƭƥĿūŠ ūĲ îŞūŠĳɠƙĿƥĚ ƑîƥĚ ǄîƑĿîƥĿūŠ ǅĿƥĺ ĲūƭƑ ČîƥĚĳūƑĿĚƙ ĚƙƥĿŞîƥĚē ĲƑūŞ ƥĺĚ ĚŞƎĿƑĿČîŕ ēîƥîɛ ǅĿƥĺ H¹¤ʋTʋȳȅ ɚĳĚŠĚƑîŕ ƥĿŞĚ ƑĚǄĚƑƙĿċŕĚŞūēĚŕɛîƙƙĚČūŠēċĚƙƥċîƙĚēūŠƥĺĚŒîĿŒĚĿŠĲūƑŞîƥĿūŠČƑĿƥĚƑĿūŠɚT ɛɍ ƙƙĚǄĚŠOȂîŠēƥĚŠsŠƭČŕĚūƥĿēĚƙĚƐƭĚŠČĚƙČūŠƥîĿŠĚēēĚĳĚŠĚƑîƥĚîŞĿŠū îČĿēƎūƙĿƥĿūŠƙɈĚĿƥĺĚƑîɚîƙƎîƑƥîƥĚūƑîƙƎîƑîĳĿŠĚɛūƑîŠÝɚîŠǋîŞĿŠūîČĿēɛǅîƙîƎƎŕĿĚē îƥ ƥĺĚƙĚ ƎūƙĿƥĿūŠƙɍ ¹ĺĚ ċĚƙƥɠǶƥ ŞūēĚŕƙ ūĲ ƎƑūƥĚĿŠ ĚǄūŕƭƥĿūŠ ǅĚƑĚ ēĚƥĚƑŞĿŠĚē ǅĿƥĺ ProtTestȂȉȇ_{ɍ¹ĺĚƎƑĚĲĚƑƑĚēqgūƎƥĿŞĿǕĚēŞūēĚŕǅîƙOT×ǅʋȳȅɚĺƭŞîŠĿŞŞƭŠūēĚǶČĿĚŠČǋ} ǄĿƑƭƙǅĿƥĺĿŠɛĲūƑOȂîŠēOT×ǅʋTʋȳȅʋGɚĚƐƭĿŕĿċƑĿƭŞîŞĿŠūîČĿēĲƑĚƐƭĚŠČĿĚƙĚƙƥĿŞîƥĚē ĲƑūŞƥĺĚĚŞƎĿƑĿČîŕēîƥîɛĲūƑsċîƙĚēūŠƥĺĚT ɍ ¡ĺǋŕūĳĚŠĚƥĿČîŠîŕǋƙĿƙ ØĿƥĺƥĺĚŠƭČŕĚūƥĿēĚƙĚƐƭĚŠČĚîŕĿĳŠŞĚŠƥƙɈĿŠĿƥĿîŕqgƥƑĚĚƙǅĚƑĚĿŠĲĚƑƑĚēƭƙĿŠĳƥĺĚ¡ĺǋqg ƎîČŒîĳĚǄĚƑƙĿūŠȄɍȁȂȉȈ_{ɈċǋŞĚîŠƙūĲîĲƭŕŕĺĚƭƑĿƙƥĿČƙĚîƑČĺîŠēƥĺĚƙƭċƥƑĚĚƎƑƭŠĿŠĳîŠē} ƑĚĳƑîĲƥĿŠĳ ɚ¬¡¤ɛ ŞĚƥĺūēɍ ƙ ƥĺĚ ¹×qʋTʋȳȅ ŞūēĚŕ ūĲ ŠƭČŕĚūƥĿēĚ ƙƭċƙƥĿƥƭƥĿūŠ ǅîƙ Šūƥ îŠūƎƥĿūŠǅĿƥĺĿŠƥĺĚ¡ĺǋqgƎîČŒîĳĚɈƥĺĚH¹¤ʋTʋȳȅŞūēĚŕǅîƙČĺūƙĚŠĲūƑîŕŕēîƥîƙĚƥƙɍ HîƑŕĿ ǄĚƑƙĿūŠ ȁɍȊȆȂȂȉȉ_{ǅîƙ ƑƭŠ ūŠ ƥĺĚ ċĚƙƥ ŠƭČŕĚūƥĿēĚ ƥƑĚĚ ĲƑūŞ ¡ĺǋqg ĲūƑ ȃ ŞĿŕŕĿūŠ} ĳĚŠĚƑîƥĿūŠƙƥūūƎƥĿŞĿǕĚƥƑĚĚƥūƎūŕūĳǋîŠēċƑîŠČĺŕĚŠĳƥĺƙɍēēĿƥĿūŠîŕŕǋɈqgƥƑĚĚƙǅĚƑĚ ĚƙƥĿŞîƥĚē ƭƙĿŠĳ ƥĺĚ ¹×qʋTʋȳȅ ŞūēĚŕ ūĲ ċîƙĚ ƙƭċƙƥĿƥƭƥĿūŠ ĿŠ ČūŞċĿŠîƥĿūŠ ǅĿƥĺ ƥƑĚĚ ċĿƙĚČƥĿūŠɠƑĚČūŠŠĚČƥĿūŠɚ¹¤ɛƙĚîƑČĺĚƙƭƙĿŠĳƥĺĚ¡À¡ɃɚǄĚƑƙĿūŠȅɍȁċȂȁɛƎîČŒîĳĚȂȉȊ_. GūƑ ĚîČĺ ūĲ ƥĺĚ ƥƑĚĚƙɈ ƥĺĚ ƑĚŕĿîċĿŕĿƥǋ ūĲ îŕŕ ƎĺǋŕūĳĚŠĚƥĿČ ĳƑūƭƎĿŠĳƙ ǅîƙ ēĚƥĚƑŞĿŠĚē ƥĺƑūƭĳĺ î ŠūŠɠƎîƑîŞĚƥƑĿČ ċūūƥƙƥƑîƎ ƑĚƙîŞƎŕĿŠĳ îŠîŕǋƙĿƙɒ ĚĿƥĺĚƑ Ȇȁȁ ƑĚƎŕĿČîƥĚƙ ūĲ qg ƥƑĚĚƙƭƙĿŠĳƥĺĚH¹¤ʋTʋȳȅŞūēĚŕîŠēƥĺĚ¬¡¤ŞĚƥĺūēƭƙĿŠĳ¡ĺǋqgɈūƑȂɈȁȁȁƑĚƎŕĿČîƥĚƙ ūĲ ŠĚĿĳĺċūƭƑɠŏūĿŠĿŠĳ ƥƑĚĚƙ ĚƙƥĿŞîƥĚē ƭŠēĚƑ ƥĺĚ qg ƙƭċƙƥĿƥƭƥĿūŠ ŞūēĚŕ ƭƙĿŠĳ ¡À¡Ƀɍ ŕŕ ƥƑĚĚƙ îƑĚ îǄîĿŕîċŕĚ ĲƑūŞ ƥĺĚ îƭƥĺūƑƙ ƭƎūŠ ƑĚƐƭĚƙƥɍ ¹ƑĚĚƙ ǅĚƑĚ ǄĿƙƭîŕĿǕĚē ǅĿƥĺ

Genetic and Antigenic Evolution of Influenza A (H3N2) Virus Neuraminidase

of Influenza A (H3N2) Virus

Neuraminidase

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Genetic Evolution of Neuraminidase

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1968 to 2009 and its Correspondence

to Haemagglutinin

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