Preface

Influenza virus remains a significant threat to humanity [1] despite the discovery of novel antiviral therapies and the continuing development of seasonal vaccines. Annual influenza epidemics exact a high toll in morbidity, estimated to be in the range of three to five million cases of severe illness, and mortality, with up to half a million deaths worldwide [2]. The twenty-first century’s first influenza pandemic caused by the commonly referred ‘swine flu’ virus strain (H1N1) 2009 has had major economic impact across the world and accounted for 414,000 confirmed cases and 5,000 deaths worldwide [3]. Human infection with the highly pathogenic avian H5N1 influenza A virus accounted for 552 confirmed cases and 322 deaths worldwide between 2003 and 2011 [4]. A recent study has estimated that a human-to-human transmissible, highly pathogenic, pandemic influenza virus could lead to ~62 million deaths worldwide [5]. The prevalence of oseltamivir-resistant influenza A(H1N1) viruses increased to 99% in many countries during 2008–2009 flu season [6] and recent isolation of oseltamivir-resistant [7] H5N1 thus necessitate the continued development of alternative antiviral agents. In this edited volume, Klenk provides an excellent review on the virology of influenza virus and its pathogenesis. As introduced in this particular contribution influenza virus sialidase (neuraminidase EC 3.2.1.18) is an enzyme (an exo-glycohydrolase) and is a tetrameric glycoprotein that consists of four identical subunits [8] anchored to the viral membrane by a long thin stalk. This enzyme effectively acts as a pair of biological scissors cleaving a-ketosidically linked sialic acids from glycoconjugates [8]. This enzyme action facilitates both the movement of virus particles through the upper respiratory tract, and, importantly, the escape of virion progeny from the surface of infected cells [8–11]. The essential nature of the influenza virus sialidase in the virus’ life cycle makes it an ideal drug discovery target. In subsequent contributions, Nicholls and colleagues provide an invaluable overview on the characterisation of carbohydrate recognition by influenza virus and a detailed analysis of virus tropism, Chan and Bennet elaborate on sialidase enzymology and Dyason and von Itzstein provide an up-to-date discussion on recent developments in influenza virus sialidase structure-based drug design.