Editing Measles (section)

==Pathophysiology==
[[File:MeaslesOsmosisPic5.jpg|thumb|upright=1.4|Drawing of the measles virus attaching to the lining of the trachea]]
[[File:Morbillo.jpg|thumb|Photomicrograph of a [[lung]] tissue specimen, showing the [[histopathology|histopathologic]] changes encountered in a case of measles [[pneumonia]]. Included in this view are numerous [[leukocyte]]s and a [[multinucleated giant cell]]. Normal alveolar [[cytoarchitecture]] has been obliterated.<ref>{{cite web |title=This photomicrograph of a lung tissue specimen, reveals the histopathologic changes encountered in a case of measles pneumonia. Included in this view, are numerous leukocytes, and a multinucleated giant cell. Normal alveolar cytoarchitecture has been obliterated. |id=859 |url=https://phil.cdc.gov/details.aspx?pid=859 |website=CDC, Public Health Image Library |publisher=U.S. Government |access-date=16 January 2024 |date=1972 |first1=Edwin P. |last1=Ewing Jr. |url-status=live |archive-url=https://web.archive.org/web/20231210152253/https://phil.cdc.gov/details.aspx?pid=859 |archive-date= 10 December 2023 }}</ref>]]

Once the measles virus contacts the [[Mucous membrane|mucosa]] lining the respiratory tract, it binds to [[SLAMF1|SLAM]] (signaling lymphocyte activation molecule, also known as CD150) on the surface of [[macrophage]]s and [[dendritic cell]]s. These cells then take up the virus. This process is mediated by the [[hemagglutinin]] protein (H) on the surface of the measles virus binding to SLAM and causing the fusion protein in the viral capsule (F) to change shape, allowing the envelope to fuse with the viral RNA and viral proteins entry. The L protein, an [[RNA-dependent RNA polymerase]], then transcribes the viral [[Sense (molecular biology)|negative-sense genome]] into a positive-sense [[Messenger RNA|mRNA]], which is [[Translation (biology)|translated]] by the cell's native [[ribosome]]s into viral proteins. These immune cells pass the virus on to other groups of immune cells, including [[B cell]]s, [[T cells]], [[thymocyte]]s, and [[hematopoietic stem cell]]s, which disseminate the virus to other organs during the [[incubation period]].<ref name="Pink Book">{{cite book |date=24 April 2024 |chapter=Chapter 13: Measles |url=https://www.cdc.gov/pinkbook/hcp/table-of-contents/chapter-13-measles.html |url-status=live |archive-url=https://web.archive.org/web/20240719164140/https://www.cdc.gov/pinkbook/hcp/table-of-contents/chapter-13-measles.html |archive-date=19 July 2024 |access-date=9 April 2025 |title=Pink Book Epidemiology and Prevention of Vaccine-Preventable Diseases |publisher=U.S. [[Centers for Disease Control and Prevention]] (CDC)}}</ref><ref name=":16" />

The initial period of infection in the lung lasts for two to three days, and ends with the first period of viremia. Five to seven days after infection begins, the second viremia occurs, and the virus infects epithelial cells.<ref name="Pink Book" /> The virus spreads along epithelial cells, initially in the respiratory tree via intercellular pores, and later in the linings of other organs and the respiratory tree via [[nectin-4]] receptors. This causes the cough seen clinically, which aerosolizes the virus and enables it to spread.<ref name="Pink Book" /><ref name="Rot2016" />