ELDERLY AND INFLUENZA

Elderly and Influenza

[Name of College]

Elderly and Influenza

Introduction

Influenza

Influenza is an acute respiratory disease which occurs due to infection by influenza viruses. It is a seasonal disease in America and often outbreaks during the winter season. Among microorganisms that reemerged periodically through history, an important representative is the influenza virus. In addition to annual outbreaks known as seasonal flu, which usually affect mostly the very young, the elderly, and individuals with underlying medical conditions, influenza regularly emerges in the form of pandemics that spread over extensive geographical areas and cause extensive morbidity and mortality in all segments of the population. The first influenza pandemic on which all authors agree occurred in 1580 and three pandemics, the 1918 to 1919 Spanish flu, the 1957 to 1958 Asian flu, and the 1968 to 1969 Hong Kong flu, occurred in the 20th century.

Three types of influenza viruses, A, B, and C, were described in humans. The single-stranded RNA viral genome contains 8 segments for types A and B and 7 for type C viruses, all required for infectivity. Two viral genes encode Hemagglutinate and neuraminidase, the proteins that decorate the viral surface as “spikes” visible by electron microscopy. Hemagglutinate is crucial for viral attachment to host cell receptors during the initial stages of the infection, and neuraminidase facilitates the subsequent cell-to-cell spread of the virus. There are 16 hemagglutinate and 9 neuraminidase subtypes that represent one of the bases for classifying influenza viruses. (Nichol, 2005)

Two characteristics of the influenza virus are central to its ability to regularly cause disease. One of them, common for RNA viruses, is the high rate of errors during replication as compared to DNA viruses. The progressive accumulation of small errors in the influenza virus genome introduces subtle changes in the resulting proteins, a process that is known as antigenic drift, and occurs constantly in all three types of influenza viruses. As a result of these small changes, influenza viruses constantly gain the ability to reinfect individuals who already were infected during previous flu seasons.

A second type of change, called antigenic shift, that occurs more rarely, was described only in type A viruses and has by far more devastating consequences. The segmented influenza virus genome enables two viruses that coinfect the same cell to exchange one or more of their genes and create new viruses, a process known as re-assortment. The 8 segments of two viruses can rearrange in 256 possible combinations, providing a great source of genetic diversity that confers new properties to the resulting strain. D. M. Morens and collaborators recently pointed out that it is more meaningful to think about influenza A viruses not as distinct entities but as “gene teams” that sometimes trade away one gene and gain new ones and acquire unique skills as a result. (Nichol, 2005)

The 1918 to 1919 Spanish flu infected 25% to 30% of the world's population and caused an estimated 50 to 100 million deaths. Its origins are debated, but the virus was shown to harbor several segments originating from avian like viruses (Prusiner, 2004). The virus responsible for the 1957 to 1958 Asian flu acquired three of its genes from viruses infecting wild ...