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A Case in Point: Influenza—We Are Unprepared
Pages 19-30

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From page 19...
... Social, political, and economic factors interact with ecological factors to drive influenza viruses to respond through biological and genetic factors, thus circumventing human defense mechanisms and, in today's increasingly global society, exerting effects on economic, social, and political life worldwide (see Figure 3-1 for a visual model of this convergence of factors)
From page 20...
... . Phylogenetic analysis of the complete HA and NA sequences supports the hypothesis that the 1918 virus was derived from avian influenza precursors and was most closely related to classical swine influenza virus.
From page 21...
... The most recent pandemic, the 1968 "Hong Kong flu," killed approximately 34,000 persons in the United States. Thus, a pattern is evident: each pandemic is followed by relatively mild yearly epidemics caused by related viruses for which the populace enjoys widespread immunity.
From page 22...
... The existence of five host-specific lineages of influenza (in humans, horses, pigs, domestic poultry, and sea mammals) indicates that aquatic avian influenza viruses have adapted to these species, overcoming differences between avian and mammalian hosts in body temperature, cell surface receptors, and mode of transmission (see Figure 3-11)
From page 23...
... protein, which is an ion channel and is the target for the antiviral agents amandatine and rimantadine. The spike glycoproteins are embedded in a lipid bilayer obtained from the host cell.
From page 24...
... and human ( 2­6 terminal sialic acid) influenza viruses and thus can act as intermediate hosts.
From page 25...
... It is noteworthy that the two influenza viruses from avian species that infected humans contain identical internal genes (PB2, PB1, PA, NP, M, NS -- black gene segments) suggesting that these gene segments contain unique regions that facilitated transmission to humans.
From page 26...
... Human Susceptibility to Infection The most severe influenza virus infection experienced by most humans is the first infection acquired after the decline of maternal antibodies; the outcome depends on the competency of the individual's immune function and on the pathogenic potential of the specific variant of influenza virus. Patients who are immunosuppressed because of disease or therapy may shed influenza virus for long periods, and a greater likelihood exists in these individuals that the virus will acquire resistance to natural immune mechanisms and to antiviral therapy.
From page 27...
... However, the direct transmission of avian H5N1 and H9N2 influenza viruses to humans in Hong Kong in 1997 and 1999 suggests the possibility that all subtypes can infect humans. The adaptation of influenza viruses to wild aquatic birds that migrate over vast distances (e.g., from southern South America to the North Slopes of Alaska)
From page 28...
... Poultry, pigs, and people are the known hosts of influenza viruses, and most of the influenza pandemics of the twentieth century have originated in China. Substantial influenza activity has been noted in Hong Kong, which is hypothesized to be a documentable epicenter for the emergence of influenza pandemics.
From page 29...
... The economic impact of an outbreak of highly pathogenic influenza was clearly seen in Hong Kong in 1997. The tourist and poultry industries collapsed because of the H5N1 "bird flu" incident, and Hong Kong suffered a severe economic downturn.
From page 30...
... The steps needed to deal effectively with interpandemic influenza can also help in preparing for an influenza pandemic. The new initiative promoting universal influenza vaccination in Ontario, Canada, can serve as a model for the world.


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