Scientists Say: Virulence

There’s a word to describe how potent a virus or bacteria is in being able to cause disease

ebola virus

Some germs cause disease easily, but others require more exposure. This is a difference in virulence. 


Virulence (noun “VEER-uh-lenss”, adjective, “VEER-uh-lent”)

In medicine, this is the potency of a germ in being able to cause an infectious disease. A virus that can infect someone with only a few particles is very virulent. One that requires a large number of viral particles has low virulence.

In a sentence

Germs can work together to stay alive virulent, even when antibiotics try to kill them.

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Power Words

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infectious  An adjective that describes a type of germ that can be transmitted to people, animals or other living things.

virulence  (in medicine) The potency of a virus, bacterium or other agent in causing infectious disease. Among a given species, some strains may cause disease with very little exposure (such as infection with a few cells). Less virulent strains may take massive exposures to create disease.

virus  Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.

Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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