Avian Influenza H5N1 Virus: An Emerging Global Pandemic

Abstract

The specter of avian influenza emerging from Asia and spreading all over the globe is causing deeper concern by the day. As we witness the H5N1 virus evolving and becoming increasingly dangerous, a major pandemic may be unavoidable. The bird flu virus has already claimed more than 140 lives worldwide as of August 2006. Should bird flu spark a global pandemic, several hundred million people could die within a matter of weeks, which is many times the number of deaths due to AIDS so far. This pathogen is completely different from seasonal influenza virus, which kills between 1 and 2 million people worldwide in a typical year. In the worst previous pandemic of 1918, more than 20 million humans died of the Spanish flu. The current bird flu virus has emerged from a pool of animals that have previously never infected humans implying that humans do not have antibodies to combat the infection. This virus also causes severe disease and high fatality within a short time span. The only remaining factor to enable the virus to cause a pandemic is if it acquires the capability of swift transmission among humans through coughing, sneezing or just a simple handshake! The evolving bird flu virus has already crossed the species barrier from chickens to other birds and mammals including pigs. Pigs possess flu virus receptors on their respiratory cells which are similar to human receptors. Thus, pigs serve as an excellent mixing vessel for the virus to exchange genes through genetic reassortment to generate an entirely new viral strain that may be capable of efficient human-to-human transmission. This chapter describes the previous pandemics, influenza virus evolution, its molecular biology, replication, zoonosis and pathogenesis. Issues on pandemic preparedness and important strategies to contain or limit the spread of this virus for the present and future are discussed.