Measles Matters
Considered eliminated in the United States in 2002, there has been a recent resurgence of measles cases attributed to growing populations of unvaccinated individuals. Caused by a paramyxovirus in the genus Morbillivirus, measles virus has shown to be a highly contagious airborne pathogen infecting 90% of those not immune that sharing living space with someone infected. Binding to epithelium of the upper respiratory tract and circulating immune cells, the virus causes fever, cough, malaise, and a diffuse rash across the body. These symptoms resolve on their own unless complications arise and was classically viewed as a common childhood illness (Naim 2014, p. 1). During our interview, Karen Williams noted measles was not considered as serious as we now might recognize it to be (Beil 2019).
Measles is a negative-sense, single-strand RNA virus with an envelope consisting of hemaggluttinin (H) and fusion (F) glycoproteins that are responsible for attachment to target cells. The receptors targeted are the CD150, also known as signaling lymphocyte activation molecule (SLAM), and nectin-4. SLAM is expressed on activated immune cells which are responding to the viral infection, allowing the virus to infect more cells and create disseminated illness. Like many other viruses, it turns the body’s defenses against itself, making it particularly dangerous for those with weakened immune systems. Nectin-4 is expressed on epithelial cells of the respiratory passages, among others, and aids in the spread of the virus through coughing and sneezing by keeping viral replication close to the mechanism for transmission (Plattet 2016, p. 1-3).
Once attached to the cell, the measles virus RNA and related proteins enter the cell to take over the cellular processes. The RNA is transcribed and translated by the host cell to form new viral particles. While some viruses cause cell lysis, measles viruses bud off from the cell causing them to be enveloped by the plasma membrane. The new viral particles then move on to infect other host cells or be transmitted to cause infection of a new host (Goering 2008, p. 40). Along with the ability to infect immune and epithelial cells, measles virus can also target the cells of the central nervous system (CNS). The exact mechanism is unknown and infection of the CNS is uncommon, but can lead to encephalitis (Naim 2014, pg. 1).
Measles virus does not possess the necessary structures for self-regulation, to replicate its RNA, synthesize proteins, respond to stimuli, or utilize energy, and is therefore not considered to be a living organism. Infection by measles involves the cell’s receptor proteins, cell membrane, nucleus and ribosomes. Cell signaling, transcription, and translation were covered in more depth throughout this course and it’s these processes that the virus takes over during infection (Steel 2019).
The first measles vaccine arrived in 1963, on the heels of the United States polio epidemic of the 1950’s that left many of the 15,000 infected each year with permanent paralysis (Anon 2017). Widespread early adoption of the measles vaccine allowed for a 60% reduction in cases within three years of its release (Hinman 2004, p. S17-S18). Mrs. Williams explained that the recent memory of polio led her to be in favor of anything that would protect her children. She believes the reality of the disease and the protection provided by vaccinating should encourage parents (Beil 2019). The recent outbreaks suggest our distance from epidemics has allowed the public to shirk responsibility for the role we play in community health, especially related to some of our most vulnerable.
References:
Beil, C.A., 2019. Measles Background with Karen Williams.
Goering, R.V. et al., 2008. Mims’ Medical Microbiology 4th ed., Mosby.
Hinman, A.R., Orenstein, W.A. & Papania, M.J., 2004. Evolution of Measles Elimination Strategies in the United States. The Journal of Infectious Diseases, 189(Supplement_1), pp.S17–S22. Available at: https://academic.oup.com/jid/article/189/Supplement_1/S17/821924 [Accessed June 21, 2019].
Naim, H.Y., 2014. Measles virus. Human Vaccines & Immunotherapeutics, 11(1), pp.21–26. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4514292/pdf/khvi-11-01-984104.pdf [Accessed June 20, 2019].
Plattet, P. et al., 2016. Measles Virus Fusion Protein: Structure, Function and Inhibition. Viruses, 8(4), p.112. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4848605/ [Accessed June 21, 2019].
Steel, C., 2019. Chapter 1: Introduction to the Study of Cell and Molecular Biology. Cell Biology.
Anon, 2017. Polio | U.S. Polio Elimination | CDC. Centers for Disease Control and Prevention. Available at: https://www.cdc.gov/polio/us/index.html [Accessed June 20, 2019].