. Author manuscript; available in PMC: 2018 Feb 22.
Published in final edited form as: Virology. 2017 Dec 22;515:92–107. doi: 10.1016/j.virol.2017.12.012
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).