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H5N1 is not yet readily transmissible from humanto human. The body temperature of birds is higherthan that of humans, at around 40 o C, and it has beensuggested that H5N1 has not yet adapted to the humanbody temperature, particularly in the upper airways.New research has also shown that H5N1 virus bindsto receptors which are present in the lungs rather thanin the upper airways 8 . Viral proliferation and sheddingthus occurs predominantly in the lower respiratorytract, reducing infectivity of droplets generated from theoropharynx during coughing and sneezing.Human disease associated with the H5N1 ‘bird flu’outbreak has been unusually severe, for reasons whichare not fully understood, though probably involveoverproduction of proinflammatory cytokines andevasion of their antiviral effects 9 . Reported mortalityrates have exceeded 50% which is much higher thanthat observed in seasonal influenza. Although human tohuman transmission has not been documented so far,it is interesting that many cases have occurred amongblood relatives. There have been no cases reportedamong persons involved in culling infected poultry,who could be expected to be at high risk of infection.This suggests that there may be a genetic element tosusceptibility, although this remains speculative.Will H5N1 cause the next pandemic? Never before hasthe emergence of an influenza pandemic been metwith such a high level of surveillance and preparedness.Close cooperation between the World Organisationfor Animal Health (OIE), and WHO, the human WorldHealth Organisation, has resulted in rapid responses tooutbreaks of avian influenza in both animals and humansworldwide. By “stamping out” infections in poultry, theopportunity for the virus to infect and mutate in humanshas been much reduced. Authorities believe it may bepossible to contain H5N1 through global cooperation.So far this has been helped by the low infectivity of thevirus to humans, and the fact that it has not adapted foreasy transmissibility between humans. If this changesor response teams become overwhelmed, then the nextpandemic may occur very soon.Should a pandemic occur, it will be met by anunprecedented public health response. The World HealthOrganisation, and governments in Australia and overseasare working on plans for containment and quarantine,administration of anti-virals and vaccines, maintenanceof essential services, and provision of acute medicalcare for up to one third of the population. Since the lastpandemic, we have developed technology allowing rapidtyping and surveillance of influenza viruses, vaccinesagainst influenza viruses, anti-viral drugs, better infectioncontrol knowledge and equipment, and sophisticatedcommunications to enable spread of information aroundthe world within minutes. However we also haverapid international transport, a much larger population,and communities whose structures have altereddramatically since the last pandemic, all of which willmake transmission of a pandemic virus easier. The rapidglobal spread of SARS illustrated the impact of a newviral respiratory illness that can be easily transmittedfrom human to human in the era of jet travel. The worldwatches with fear, awe, and hope that a killer pandemicwill not occur again.References1. Hinshaw VS, Webster RG. The natural history ofinfluenza A viruses. In: Beare AS, editor. 79-104. Basicand applied influenza research. Boca Raton, Fla., CRCPress, Inc.1982.2. Gerhard W, Mozdanowska K, Zharikova D. Prospectsfor universal influenza virus vaccine. Emerg Infect Dis.2006;12(4):569-74.3. Treanor JJ. Influenza virus. 2060-85. In: Mandell,Douglas, and Bennett’s principles and practice ofinfectious diseases. 6 th ed. Mandell GL, Bennett JE,Dolin R, editors. Philadelphia, Pen; Elsevier ChurchillLivingstone; 2005.4. Webster RG, Bean WJ, Gorman OT, et al. Evolutionand ecology of influenza A viruses. Microbiol Rev.1992;56(1):152-79.5. Tumpey TM, Basler CF, Aguilar PV, et al.Characterization of the reconstructed 1918 Spanishinfluenza pandemic virus. Science. 2005;310:77-80.6. Guan Y, Poon LLM. Cheung CY, et al. H5N1 influenza:a protean pandemic threat. PNAS. 2004;101(21):8156-61.7. Schnurrenberger, PR, Woods GT, Martin RJ. Serologicevidence of human infection with swine influenzavirus. Am Rev Respir Dis. 1970;102:356-361.8. Shinya K, Ebina M, Yamada S, et al. Avian flu:influenza virus receptors in the human airway. Nature.2006;440(7083):435-6.9. Seo SH, Hoffman E, Webster RG. Lethal H5N1influenza viruses escape host anti-viral cytokineresponses. Nat Med. 2002;8(9):950-4.