. Author manuscript; available in PMC: 2016 Apr 4.
Published in final edited form as: Virology. 2015 Dec 31;489:116–127. doi: 10.1016/j.virol.2015.12.005
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).