The Science of Influenza

                  Have you ever gotten sick and wondered why or what is causing your sickness? There are many reasons to get sick, but one big one is the influenza virus. The influenza virus, most commonly known as the flu, is generally at large during the winter months. The influenza virus is an infection in the respiratory tract that is caused by related viruses in the Orthomyxoviridae family.

                  Influenza viruses are categorized into four main types, which are further divided based on similarities. The four types of influenza are type A, B, C, and D. Influenza type A viruses are the viruses that cause influenza epidemics, and type B viruses cause smaller outbreaks. Influenza type C viruses cause mild respiratory illness, and type D viruses don’t infect humans at all, but instead infect pigs and cattle. Each type is different enough that immunity against one type of influenza can’t protect against any other influenza types. Every influenza virus type has hemagglutinin “H” and neuraminidase “N” proteins on its surface. Many combinations of the two proteins are possible because there are 16 hemagglutinin proteins, H1-H16; and 9 neuraminidase proteins, N1-N9. These proteins also act as antigens. Antigens are identified molecular structures found on the surface of viruses that the immune system recognizes and can cause your body to create antibodies.

                  Influenza A viruses can change in two ways, antigenic drifts, and antigenic shifts. An antigenic drift produces new virus variants the body doesn‘t recognize. This causes the person to get sick again. Antigenic shifts occur when human influenza A and animal influenza A mix. When this happens, it creates a new human influenza A subtype.“Clades” and “Sub-Clades” are ways influenza A subtypes can further be broken down into categories. They subdivide influenza viruses based on similarities in their genes. Unlike type A, type B viruses don’t get categorized into subtypes, instead, they are further divided into two lineages; B/Yamagata and B/Victoria. Like influenza type A, though, influenza B lineages can be divided into “Clades” and “Sub-Clades.” Influenza B also tends to change slower in its genes and antigenic properties.

                  Outbreaks of influenza are more fatal to older people and younger children. This is due to a hyper-reaction of the immune system, causing an overproduction of inflammatory substances called cytokines. When excessive amounts of cytokines are released, it causes severe inflammation, especially in the lungs. So individuals who have weakened or not fully developed immune systems, cannot create a protective lethal immune response.

                  One infection in the respiratory tract is the influenza virus. Even though we can’t see them, viruses have so much science in them. For this reason, they are so interesting and fascinating. With a whole world around us, there are still so many viruses waiting to be discovered!

   Sources:

Britannica, The Editors of Encyclopaedia. “influenza”. Encyclopedia Britannica, 5 Dec. 2022, https://www.britannica.com/science/influenza. Accessed 22 February 2023.

CDC, Dec. 2, 2022

https://www.cdc.gov/flu/about/viruses/types.htm

Morgridge

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