flu 1918 review - Review The origin of the 1918 pandemic...

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Unformatted text preview: Review The origin of the 1918 pandemic influenza virus: a continuing enigma Ann H. Reid and Jeffery K. Taubenberger Correspondence Jeffery Taubenberger [email protected] Division of Molecular Pathology, Department of Cellular Pathology and Genetics, Armed Forces Institute of Pathology, 1413 Research Blvd, Building 101, Room 1057, Rockville, MD 20850-3125, USA Influenza A virus is a major public health threat, killing more than 30 000 per year in the USA alone, sickening millions and inflicting substantial economic costs. Novel influenza virus strains emerge periodically to which humans have little immunity, resulting in devastating pandemics. The 1918 pandemic killed nearly 700 000 Americans and 40 million people worldwide. Pandemics in 1957 and 1968, while much less devastating than 1918, also caused tens of thousands of deaths in the USA. The influenza A virus is capable of enormous genetic variability, both by continuous, gradual mutation and by reassortment of gene segments between viruses. Both the 1957 and 1968 pandemic strains are thought to have originated as reassortants, in which one or both human-adapted viral surface proteins were replaced by proteins from avian influenza virus strains. Analyses of the surface proteins of the 1918 pandemic strain, however, suggest that this strain may have had a different origin. The haemagglutinin gene segment of the virus may have come directly from an avian source different from those currently circulating. Alternatively, the virus, or some of its gene segments, may have evolved in an intermediate host before emerging as a human pathogen. Determining whether pandemic influenza virus strains can emerge via different pathways will affect the scope and focus of surveillance and prevention efforts. INTRODUCTION That there will be epidemics of influenza every year is a virtual certainty. That they will begin in late winter and last a month or two is also very likely (Brammer et al ., 2002). However, beyond those general rules, predicting the timing, magnitude and severity of influenza epidemics is a formidable public health challenge. Influenza A viruses circulate widely in humans and spread in several epide- miologically distinct ways: as localized outbreaks, as yearly regional epidemics and, occasionally, as global pandemics. In the USA, influenza leads to the hospitalization of over 100 000 and kills over 30 000 people in an average year (Simonsen et al ., 2000; Thompson et al ., 2003). Every 2 or 3 years, influenza epidemics boost the yearly number of deaths past the average, causing 10 000–15 000 additional deaths. Occasionally, and unpredictably, influenza sweeps the world, infecting 20 to 40 % of the population in a single year. In these pandemic years, which have occurred every 10 to 50 years for at least several centuries, the number of deaths can be dramatically above average (Beveridge, 1977; Cox & Subbarao, 2000; Wright & Webster, 2001). It is very likely that influenza will return in pandemic form. Recently,likely that influenza will return in pandemic form....
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This note was uploaded on 07/12/2011 for the course BIO 620 taught by Professor Hardy during the Spring '11 term at University of Florida.

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flu 1918 review - Review The origin of the 1918 pandemic...

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