Introduction to the Flu Virus

The flu virus (also known as the influenza virus) belongs to the virus family Orthomyxoviridae. This viral family is subdivided into three genera: Influenzavirus A, B; Influenzavirus C; and a group of unnamed Thogoto-like viruses (which are tick-borne viruses). The main virus of the family is the influenza virus.

The physical characteristics of influenza viruses are that they are single-stranded, RNA viruses enclosed in a helical nucleocapsid. On the outside, these viruses are enveloped. Two important proteins are found on surface of this envelope: hemagglutinin and neurominidase. These proteins are important for binding to host cells and cleaving off from the host cell, respectively.

From The Transmission of Epidemic Influenza by R. Edgar Hope-Simpson, Plenum Press. 1992. p 45.

The symptoms of the flu include the abrupt onset of a high fever, sore throat, dry cough, general body pain, headache, and tiredness. This may last for about three to seven days, but the cough and tiredness may last a while longer. Transmission is by respiratory droplets, and the incubation period is generally one to four days.

Epidemics tend to occur during the winter months in the Northern Hemisphere, and during the summer months in the Southern Hemisphere. Every year, they are a major cause of death among the elderly and the immunocompromised.

Influenza C commonly infects children, but is not a major cause of disease. Influenza A and B both cause disease, and are both capable of undergoing antigenic drift (meaning that they both mutate because of point mutations). Influenza A is also able to drastically alter its genome, because it is capable of undergoing antigenic shift. What this means is that influenza A is capable of undergoing genetic recombination between viral stains. This can, and has, led to major worldwide pandemics.

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