Virus

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.

Virus

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.

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