S. Stertz, P. Palese
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This chapter on genome plasticity of influenza viruses discusses the current knowledge of viral factors. Influenza viruses have caused devastating pandemics and epidemics in the past, and they continue to be a major health problem causing a huge economic burden worldwide. Thus, it is important to understand the characteristics of influenza viruses and to elucidate the extensive interplay between virus and host. Besides the eight structural proteins, influenza A virus encodes the three nonstructural proteins NS1, NEP, and PB1-F2. Influenza viruses pose a major problem for human health and thereby cause a substantial economic burden. The influenza pandemics which occurred in the past century share the fact that new subtypes of influenza A viruses were introduced into the human population. There are two classes of US Food and Drug Administration-approved drugs against influenza: inhibitors of the ion channel M2 and NA inhibitors. The first group comprises the adamantanes, rimantadine and amantadine, which act by inhibiting the viral ion channel M2 and thereby block the step of uncoating during virus entry. It becomes clear that circulating influenza viruses need to be closely monitored for resistance to the available drugs. Within the same host species genetic polymorphisms may occur and influence the ability of the virus to use the host proteins. For influenza viruses to survive, they need to be transmitted from host to host. The development of reverse genetics techniques has greatly advanced understanding of the virus and its replication cycle.