Reassortment of influenza virus strains (antigenic shift) resulting in new strains. Reassortment occurs when two closely related segmented viruses infect the same cell, resulting in drastic antigenic changes and formation of new viral strains. In this example, human flu virus and swine flu virus infect the lung cell of swine. Following replication of viral RNA segments of both viruses in the same cells, progeny viruses are assembled as a result of reassortment of newly synthesized RNA segments that may come from both viruses. Reassortment of newly synthesized RNA segments generates parental types, new hybrid viruses, and hundreds of other possible combinations. Some of these hybrid viruses could become new strains causing severe epidemics or pandemic influenza. Source: Pathogenic Viruses, Sherris Medical Microbiology, 6e Citation: Ryan KJ, Ray C. Sherris Medical Microbiology, 6e; 2014 Available at: http://accessmedicine.mhmedical.com/DownloadImage.aspx?image=/data/Books/1020/rya_ch6_f022.png&sec=56988119&BookID=1020&ChapterSecID=56968657&imagename= Accessed: December 18, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved