One of the author's funding sources was not acknowledged in the published manuscript. The authors wish to add the following funding information to the Funding section: "This work was supported by grants to LM from NIH Models of Infectious Disease Agent Study (MIDAS) (U01-GM087719-01), the James S. McDonnell Foundation, and NSF (DEB-0749097) and grants to BP from CIHR(PTL-97125 and PAP-93425) and the Michael Smith Foundation for Health Research."
Footnotes
Competing Interests: No competing interests declared.
