MICROARRAY/MICROBIOLOGY

Microarray/Microbiology



Microarray/Microbiology

Section 1: Pathology of influenza infections: systems biology brings cohesion to disparate pictures and highlights systemic consequences of infection

Influenza is also known as the flu, is a respiratory illness caused by the influenza virus that results in mild to severe illness. According to the Centers for Disease Control and Prevention (CDC), 5% to 20% of the U.S. population gets the flu each year, with 200,000 hospitalizations and 36,000 deaths. Its presentation can be similar to the common cold. The flu is spread via the same mechanism as the common cold (aerosols released by coughing or sneezing, touching the infected surfaces and then touching the mouth or nose, and so on). Risk of transmission is between 1 day before the development of symptoms and up to 5 days after. Pulmonary function can be diminished for up to several weeks in athletes with the flu (Korteweg, 2008).

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 (Pantin-Jackwood & Swayne, 2010).

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 hemagglutinin and neuraminidase, the proteins that decorate the viral surface as “spikes” visible by electron microscopy. Hemagglutinin 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 hemagglutinin and 9 neuraminidase subtypes that represent one of the bases for classifying influenza viruses.

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 (Carole, 2011).

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 ...