The latest Journal of Virology, had an interesting article that has the ability to send chills down your spine…”High genetic compatibility between swine-origin H1N1 and highly pathogenic avian H5N1 influenza viruses,” by a group of Japanese and American researchers.

First, what is reassortment? Reassortment is the mixing of the genetic material into new combinations. It is particularly occurs when two similar viruses (think influenza) infect the same cell and exchange genetic material.   Reassortment is responsible for some of the major genetic shifts in the history of the influenza virus. The 1957 and 1968 pandemic influenza strains were caused by reassortment between an avian virus and a human virus.  Our H1N1 pandemic virus was an unusual mix of swine, avian and human influenza genetic material.

viral subunit reassortment
A very cool website shows the reassortment process via animation at the cellular level….check it out. http://www.hhmi.org/biointeractive/animations/subunit/sub_middle_frames.htm

So therefore, reassortment is an important mechanism for the evolution of influenza viruses. In this study the researchers co-infected cultured cells with the pandemic swine-origin influenza virus and a contemporary H5N1 virus and found that the two viruses have high genetic compatibility. Studies in human lung cell lines indicated that some reassortants had better growth kinetics than their parental viruses. Therefore, gulp, the researchers concluded that reassortment between these two viruses can occur and could create pandemic H5N1 viruses.

http://jvi.asm.org/cgi/content/short/JVI.01140-10v1