Transmission of Ebola Viruses: What We Know and What We Do Not Know doi: 10.1128/mBio.00137-15 19 February 2015 mBio vol. 6 no. 2 e00137-15  Michael T. Osterholm a, Kristine A. Moore a, Nicholas S. Kelley a, Lisa M. Brosseau b, Gary Wong c, Frederick A. Murphy d, Clarence J. Peters d, James W. LeDuc d, Phillip K. Russell e, Michel Van Herp f, Jimmy Kapetshi g, Jean-Jacques T. Muyembe g, Benoit Kebela Ilunga h, James E. Strong c, Allen Grolla c, Anja Wolz f, Brima Kargbo i, David K. Kargbo i, Pierre Formenty j, David Avram Sanders k, Gary P. Kobinger c + Author Affiliations 1.         aCenter for Infectious Disease Research and Policy, University of Minnesota, Minneapolis, Minnesota, USA 2.         bDivision of Environmental and Occupational Health Sciences, University of Illinois at Chicago, Chicago, Illinois, USA 3.         cNational Laboratory for Zoonotic Diseases and Special Pathogens, Public Health Agency of Canada, Winnipeg, Canada 4.         dThe Galveston National Laboratory, University of Texas Medical Branch, Galveston, Texas, USA 5.         eSabin Vaccine Institute, Washington, DC, USA 6.         fMedical Department Unit, Médecins sans Frontières, Brussels, Belgium 7.         gInstitut National de Recherche Biomédicale, Kinshasa, Democratic Republic of the Congo 8.         hMinistry of Health, Kinshasa, Democratic Republic of the Congo 9.         iMinistry of Health and Sanitation, Freetown, Sierra Leone 10.     jDepartment of Epidemic and Pandemic Alert and Response, World Health Organization, Geneva, Switzerland 11.     kDepartment of Biological Sciences, Purdue University, Lafayette, Indiana, USA 1.         Address correspondence to Michael T. Osterholm, 1.         Editor Michael J. Imperiale, University of Michigan Next Section ABSTRACT Available evidence demonstrates that direct patient contact and contact with infectious body fluids are the primary modes for Ebola virus transmission, but this is based on a limited number of studies. Key areas requiring further study include (i) the role of aerosol transmission (either via large droplets or small particles in the vicinity of source patients), (ii) the role of environmental contamination and fomite transmission, (iii) the degree to which minimally or mildly ill persons transmit infection, (iv) how long clinically relevant infectiousness persists, (v) the role that “superspreading events” may play in driving transmission dynamics, (vi) whether strain differences or repeated serial passage in outbreak settings can impact virus transmission, and (vii) what role sylvatic or domestic animals could play in outbreak propagation, particularly during major epidemics such as the 2013–2015 West Africa situation. In this review, we address what we know and what we do not know about Ebola virus transmission. We also hypothesize that Ebola viruses have the potential to be respiratory pathogens with primary respiratory spread. Note:  Drs. Michael T. Osterholm [PhD, MPH] and Frederick A. Murphy [DVM, PhD] serve on the One Health Initiative Team’s Honorary Advisory Board  Dr. C.J. Peters [MD] is a longstanding One Health supporter