Influenza

Article By:

Quarles, John M. Department of Medical Microbiology and Immunology, Texas A&M University, College Station, Texas.

Arden, Nancy H. Department of Epidemiology and Biostatistics, Texas A&M University, College Station, Texas.

Last reviewed:June 2019

DOI:https://doi.org/10.1036/1097-8542.343800

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• Influenza, published June 2014:Download PDF Get Adobe Acrobat Reader

An acute respiratory viral infection, commonly known as the flu, characterized by fever, chills, sore throat, headache, body aches, and severe cough. Influenza is an infectious disease caused by viruses in the family Orthomyxoviridae. These viruses infect mammals (including humans) and birds and can be transmitted from one type of animal to another. The various viruses that cause influenza are similar in structure, consisting of a roughly spherical protein capsid that is 80–120 nanometers (nm) in diameter, surrounded by a viral envelope (Fig. 1). In general, many viruses (including the common cold) can cause respiratory infections, but influenza viruses are more likely to cause severe illness and to result in serious medical complications. Although gastrointestinal symptoms may sometimes accompany influenza infection, especially in children, the term “stomach flu” is a misnomer for gastrointestinal illnesses, which are caused typically by a variety of other viruses, bacteria, or other agents. See also: Common cold; Infectious disease; Pathogen; Respiratory system disorders; Virus; Virus classification

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