The mode of infection transmission has profound implications for effective containment by public health interventions. The mode of smallpox transmission was never conclusively established. Although, “respiratory droplet” transmission was generally regarded as the primary mode of transmission, the relative importance of large ballistic droplets and fine particle aerosols that remain suspended in air for more than a few seconds was never resolved. This review examines evidence from the history of variolation, data on mucosal infection collected in the last decades of smallpox transmission, aerosol measurements, animal models, reports of smallpox lung among healthcare workers, and the epidemiology of smallpox regarding the potential importance of fine particle aerosol mediated transmission. I introduce briefly the term anisotropic infection to describe the behavior of Variola major in which route of infection appears to have altered the severity of disease.
Keywords: smallpox, bioterrorism, biodefense, variola virus, air microbiology, communicable diseases, airborne infection transmission, contact infection transmission
Citation: Milton DK (2012) What was the primary mode of smallpox transmission? Implications for biodefense. Front. Cell. Inf. Microbio. 2:150. doi: 10.3389/fcimb.2012.00150
Received: 13 August 2012; Paper pending published: 12 September 2012;
Accepted: 13 November 2012; Published online: 29 November 2012.
Edited by:Chad J. Roy, Tulane University, USA
Reviewed by:Vincent J. Starai, The University of Georgia, USA
Copyright © 2012 Milton. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Donald K. Milton, Maryland Institute for Applied Environmental Health, School of Public Health, University of Maryland SPH Building #255, College Park, MD 20742, USA. e-mail: firstname.lastname@example.org