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What is a virus?

Viruses infect every living thing and may be as old as life itself. Everywhere there’s life on Earth, from high up in the atmosphere to deep in the ocean, there are viruses. The vast majority aren’t harmful to humans at all, but to understand the few that are—like the SARS CoV-2 virus behind the COVID-19 pandemic—we must learn about the connections between humans, viruses, other organisms, and the ecosystems we co-habit. For thousands of years, humans didn’t even know that viruses existed. They were too small to be seen by early microscopes, and it wasn’t until the late 19th century that a scientist attached the word “virus” to a category of microbes that can cause disease. Today, we’ve learned that viruses are found in all groups of living things, from bacteria to plants and animals. Some pose no threat to our health, while others cause infections, including human diseases like smallpox and AIDS. Created with the support of the City of New York Department of Health and Mental Hygiene. © 2021 City of New York. *** SOURCES: Andiman, Warren. Animal Viruses and Humans, a Narrow Divide: How Lethal Zoonotic Viruses Spill over and Threaten Us. Philadelphia, Paul Dry Books, 2018. Chakraborty, Arup, and Andrey Shaw. Viruses, Pandemics, and Immunity. Cambridge, Massachusetts; London, England MIT Press, 2021. Crawford, Dorothy H. The Invisible Enemy: A Natural History of Viruses. Oxford, Oxford University Press, 2002. Desalle, Rob. Epidemic!: The World of Infectious Diseases. New York, The New Press, 1999. Maxmen, Amy, and Smriti Mallapaty. “The COVID Lab-Leak Hypothesis: What Scientists Do and Don’t Know.” Nature, 8 June 2021, www.nature.com/articles/d41586-021-01529-3, 10.1038/d41586-021-01529-3. Accessed 2 Dec. 2021. Quammen, David. Spillover. London, The Bodley Head Ltd, 2012. Zimmer, Carl. Planet of Viruses. S.L., Univ of Chicago Press, 2021. Created by American Museum of Natural History.

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