If you are experiencing a medical emergency please dial 911 immediately
A virus is a microscopic organism that causes infection and disease. Viral illnesses can range from mild to severe. Some examples are the common cold, West Nile virus, polio, and smallpox.
Last Revised: July 9, 2012
Author: Healthwise Staff
Medical Review: E. Gregory Thompson, MD - Internal Medicine & Christine Hahn, MD - Epidemiology
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