This "kill em all" approach has been used forever, but as we have seen with antibiotics, killing off all the micro-organisms in a host can have harmful effects, since many of these are beneficial or even essential. The same thing is true of viruses, they are not all "bad". > Although viruses are most often studied as pathogens, many are beneficial to their hosts, providing essential functions in some cases and conditionally beneficial functions in others. Beneficial viruses have been discovered in many different hosts, including bacteria, insects, plants, fungi and animals. How these beneficial interactions evolve is still a mystery in many cases but, as discussed in this Review, the mechanisms of these interactions are beginning to be understood in more detail. Although it cannot be denied that viruses have caused extensive disease and suffering for humans and domesticated plants and animals, there are many viruses that are clearly mutualistic. Some are essential for the survival of their hosts, others give their hosts a fighting edge in the competitive world of nature and some have been associated with their hosts for so long that the line between host and virus has become blurred. SEE: The good viruses: viral mutualistic symbioses Marilyn J. Roossinck Nature Reviews | Microbiology Volume 9 | Feb 2011 *********************************************** The BEE-L mailing list is powered by L-Soft's renowned LISTSERV(R) list management software. For more information, go to: http://www.lsoft.com/LISTSERV-powered.html Guidelines for posting to BEE-L can be found at: http://honeybeeworld.com/bee-l/guidelines.htm