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Introduction to Viruses

Author(s): Christine Herrmann, PhD

How Do New Viruses Emerge?

An emerging virus is one that has either recently appeared in a population or is rapidly expanding its range of hosts and geographic locations. Viruses, especially RNA viruses, acquire mutations and evolve over time. When viruses accumulate a significant number of changes in their genetic material, they may no longer be recognized by a host’s immune system. Therefore, they may be seen as a “new” virus. Influenza virus, which causes the flu, mutates rapidly and can cause seasonal epidemics; this is the reason a flu shot is necessary every year.

Changes in a virus due to evolution also can lead to a change in the host range of a virus, in which case a virus may become capable of infecting a new species. For example, the 1918 bird flu virus mutated enough that it acquired the ability to infect humans, with devastating consequences. Viruses also can be introduced into new hosts and new geographic locations as a result of human activity. As the human population expands into previously uninhabited areas, there is increased contact between humans and animals. Many human emergent viruses have their origins in animals.


Funded by the following grant(s)

Video and transcript courtesy of Wah Chiu, PhD, National Center for Macromolecular Imaging at Baylor College of Medicine. Funding for the video provided by NCMI, NIH.