1. Image is in public domain or freely licenses, obtained from www.wikimedia.org, public domain.
2. Atlas of virus diagrams;Ackermann,1995
3. Image from the Centers for Disease Control and Prevention Public Health Image Library, image is in the public domain.
4. http://www.cdc.gov/foodborneburden/2011-foodborne-estimates.html
5. The history of food irradiation;Nordion,2010