Influenza, respiratory syncytial virus and SARS

Acute lower respiratory tract infections (LRTIs) are a major worldwide health problem, particularly in childhood. About 30-50% of acute LRTIs are viral in origin; of these, influenza and respiratory syncytial virus are associated with the greatest disease burden in humans. Many different influenza A viruses occur naturally in animal reservoirs, and present a constant threat of zoonotic infections and global pandemics. The pandemic (H1N1) influenza virus that emerged in humans in 2009 contained a unique combination of genes originating in swine and the global human population was highly susceptible to the novel strain. The emergence of the severe acute respiratory syndrome coronavirus in 2003, and the ensuing worldwide epidemic, highlights the fact that respiratory viral infections in humans may originate in animals. Preventative measures for influenza include annual vaccination and treatment with antiviral drugs such as the neuraminidase inhibitors oseltamivir and zanamivir. Subtype-dependent resistance to antivirals can develop and should be closely monitored.